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Ablation of Atypical Atrioventricular Nodal Reentrant Tachycardia. Introduction: Published reports of radiofrequency ablation of atypical atrioventricular nodal reentrant tachycardia (AVNRT) have been limited. We present our experience in 10 consecutive patients with atypical AVNRT who underwent radiofrequency ablation of the 'slow' AV nodal pathway. Methods and Results: There were 9 females and I male; their mean age was 44 ± 19 years (± SD). The mean AVNRT cycle length and ventriculoatrial (VA) interval at the His position (luring AVNRT were 340 ± 50 msec and 200 ± 70 msec, respectively. The slow pathway was successfully ablated in all patients with a mean of 10 ± 7 radiofrequency energy applications in the posteroseptal right atrium near the coronary sinus os. The mean procedure duration was 100 ± 35 minutes. There were no complications. In 4 patients, target sites were identified during sinus rhythm by mapping for possible slow pathway potentials. in the other 6 patients, tare gel sites were identified by mapping retrograde atrial activation during AVNRT or ventricular pacing. The VA times at successful target sites were a mean of 45 ± 30 msec less than the VA time at the His catheter during AVNRT. There were no differences in success rate, number of radiofrequency energy applications, or procedure duration between patients in whom mapping was guided by possible slow pathway potentials or by retrograde atrial activation. During 6 ± 3 months of Fellow-up. I patient had a recurrence of atypical AVN RT and underwent a second ablation procedure, which was successful. Conclusion: Radiofrequency ablation of atypical AVNRT can be safely and effectively accomplished when target sites are identified based either on possible slow pathway potentials during sinus rhythm or retrograde atrial activation times during tachycardia. [ABSTRACT FROM AUTHOR]

Background: Adolescent idiopathic scoliosis (AIS) affects up to 5% of the population. The efficacy of school-aged screening remains controversial since it is uncertain which curvatures will progress following diagnosis and require treatment. Patient demographics, vertebral morphology, skeletal maturity, and bone quality represent individual risk factors for progression but have yet to be integrated towards accurate prognostication. The objective of this work was to develop composite machine learning-based prediction model to accurately predict AIS curves at-risk of progression., Methods: 1870 AIS patients with remaining growth potential were identified. Curve progression was defined by a Cobb angle increase in the major curve of ≥6° between first visit and skeletal maturity in curves that exceeded 25°. Separate prediction modules were developed for i) clinical data, ii) global/regional spine X-rays, and iii) hand X-rays. The hand X-ray module performed automated image classification and segmentation tasks towards estimation of skeletal maturity and bone mineral density. A late fusion strategy integrated these domains towards the prediction of progressive curves at first clinic visit., Findings: Composite model performance was assessed on a validation cohort and achieved an accuracy of 83.2% (79.3-83.6%, 95% confidence interval), sensitivity of 80.9% (78.2-81.9%), specificity of 83.6% (78.8-84.1%) and an AUC of 0.84 (0.81-0.85), outperforming single modality prediction models (AUC 0.65-0.78)., Interpretation: The composite prediction model achieved a high degree of accuracy. Upon incorporation into school-aged screening programs, patients at-risk of progression may be prioritized to receive urgent specialist attention, more frequent follow-up, and pre-emptive treatment., Funding: Funding from The Society for the Relief of Disabled Children was awarded to GKHS., Competing Interests: Declaration of interests KC has previously received research funding and honoraria from AO spine, Nuvasive, Medtronic, Globus, ICISO, the Japanese Orthopaedic Association, and the University of North Carolina. He is a member of the AOSpine Knowledge Forum Steering Committee, as well as a Nominating Committee Member of the Scoliosis Research Society. All the other authors report no conflicts., (Copyright © 2023 The Author(s). Published by Elsevier B.V. All rights reserved.)

There is a global increase in the older population. Unfortunately, dental conditions in the older population can sometimes be poor as a result of worsened physical conditions and the cumulative damage caused by dental diseases in the past. Many suffer from oral diseases such as dental caries and periodontal disease but receive no regular dental care. Oral conditions and systemic problems are interrelated. Chronic medical problems and polypharmacy are common among them. These conditions may lead to xerostomia with or without a decrease in saliva output. Additionally, many older adults have deteriorated masticatory function associated with physical health issues such as frailty. Preventive measures are crucial to stop oral diseases from progressing and the replacement of missing teeth is needed when masticatory function is impaired. Older adults also suffer a higher risk of oral cancer because of their less resilient but more permeable oral mucosa. With the increasing need for elderly dental care, dentists should equip themselves with knowledge and skills in geriatric dentistry. They should help older adults to develop and maintain the functional ability that enables well-being in older age. This communication article aims to discuss the relevant medical conditions, common dental diseases, and dental care for older adults.

Objectives: This study aimed at revealing the caregiving challenges of the caregivers of people with dementia (PwD) during the COVID-19 pandemic when daycare service was stopped as an infection control measure, and discussed ways to help PwD and their family caregivers to maintain their well-being in the era of the pandemic., Methods: Between April and May 2020, a cross-sectional survey was conducted in 152 family caregivers of PwD who were clients of daycare service prior to the pandemic. The survey examined caregivers' stress and challenges faced during daycare service cessation, their perceived needs for continuation of daycare service, and observed changes in functional status of PwD. Regression analyses were performed to explore the associated factors of caregiving stress and preference for continuation of daycare service., Results: Family caregivers of PwD experienced greater caregiving stress after cessation of daycare service. Infection was their main challenge in caregiving, and their physical and emotional health was adversely affected by the longer time commitment with PwD under the stay-home policy. Older age of caregivers, greater emotional and communication problems of PwD, and more time spent with PwD were associated with greater caregiving stress. More than one-third of the participants preferred the continuation of daycare service during the pandemic., Conclusions: Policy makers should consider the well-being of PwD and their caregivers when planning infection control measures. Daycare service with enhanced infection controlled measures should remain available to PwD during the COVID-19 pandemic., (© 2021 John Wiley & Sons Ltd.)

Background: Sjögren's syndrome (SS) patients are prone to caries development due to reduction of salivary flow. Topical fluoride is commonly prescribed for caries prevention., Methods: In this 24-month randomized, double-blind, placebo-controlled clinical trial, SS patients were randomly assigned to receive either fluoride varnish or placebo gel quarterly. Development and arrest of caries at the coronal and root surfaces were recorded at 12-month and 24-month and compared to that of the baseline. Effect of fluoride varnish on oral Candida and lactobacilli colonization was explored by comparing baseline oral microbiological assessments to data obtained at 12-month and 24-month., Results: Seventy-eight SS patients (mean age = 50 years, 2 men) completed this trial. At 24-month, the mean new coronal enamel caries were 1.6 surfaces in both groups, and new dentin caries were 1.4 and 2.7 surfaces in the fluoride and placebo group respectively (p > 0.05). Mean arrested caries were 0.6 and 0.7 surfaces for fluoride and placebo groups respectively and that of root caries were 0.3 and 0.1 surfaces (p > 0.05). The mean oral Candida count was reduced by 30 % in the fluoride group but increased 61 % in the placebo group while no change in oral lactobacilli counts in both groups at 24 months (p > 0.05). SS patients receiving fluoride varnish were significantly less likely to develop dentin caries (p < 0.05). In contrast, those with high baseline DMFS scores (p = 0.05), harbored mixed Candida species (p < 0.05), or unstimulated whole saliva at low pH (p < 0.01) were significantly more likely to develop dentin caries., Conclusions: Results of this randomized clinical trial did not provide clear evidence to support or refute that quarterly applications of fluoride varnish can prevent development of dental caries in people with Sjögren's syndrome., Trial Registration: This study was retrospectively registered at the ISRCTN registry ( ISRCTN85164658 ) on 9 Sept 2016 and was funded by the Research Grant Council of Hong Kong.

Purpose: The aim of this research was to evaluate the effectiveness of a clinical instructional video with a structured worksheet for independent self-study in a complete denture program., Methods: 47 multilingual dental students completed a task by watching an instructional video with subtitles regarding clinical complete denture procedures. After completion, students evaluated their learning experience, and 11 students participated in focus group interviews to gain further insight. A mixed-methods approach to data collection and analysis provided descriptive statistical results and a grounded theory approach to coding identified key concepts and categories from the qualitative data., Results: Over 70% of students had favorable opinions of the learning experience and indicated that the speed and length of the video were appropriate. Highly positive and conflicting negative comments regarding the use of subtitles showed both preferences for subtitles over audio and vice versa. The use of a video resource was considered valuable as the replay and review functions allowed better visualization of the procedures, which was considered a good recap tool for the clinical demonstration. It was also a better revision aid than textbooks. So, if the students were able to view these videos at will, they believed that videos supplemented their self-study. Despite the positive response, videos were not considered to replace live clinical demonstrations., Conclusions: While students preferred live demonstrations over the clinical videos they did express a realization of these as a supplemental learning material for self-study based on their ease of access, use for revision, and prior to clinical preparation., (Copyright © 2015 Japan Prosthodontic Society. Published by Elsevier Ltd. All rights reserved.)

The genetic structure of two related yeast species, one sexual and one asexual, was compared using polymorphic DNA markers. Although both yeasts propagate by asexual budding of haploid cells, Metschnikowia borealis reproduces sexually when compatible strains come in contact. To what extent this has occurred in nature was not known. As Candida ipomoeae is a closely related, asexual species, the two yeasts provide an excellent model system to assess the role of sexual reproduction in a biogeographic context. Natural isolates of the two species were characterized using several polymorphic DNA markers. As predicted for an organism whose reproduction is strictly clonal, C. ipomoeae exhibited low haplotype diversity, high linkage disequilibrium, and high population differentiation. In contrast, M. borealis had unique haplotypes in most isolates, lower population differentiation, and little linkage disequilibrium, demonstrating that sexual recombination is prevalent. Geographic gradients were identified in both species, indicating that historical and climatic factors both play a role in shaping the populations. The spatial structure is also thought to be influenced by the ecology of the small floricolous beetles (family Nitidulidae) that vector the yeasts. For example, Hawaiian strains of C. ipomoeae show evidence of having undergone a genetic bottleneck, most likely when the vector was introduced to the islands. The two haplotypes found in Hawaii were nearly identical and were also found in North and Central America. M. borealis had a more continuous distribution where the genetic markers follow latitudinal and longitudinal gradients.

Background: Rheumatic heart disease remains a major public health problem in developing countries with its very high prevalence. Rheumatic and congenital heart disease are significant causes of morbidity and mortality among Nepalese schoolchildren. The aim of our study was to determine the prevalence of rheumatic and congenital heart disease among schoolchildren of the Kathmandu valley in Nepal., Methods and Results: The study included 9420 students, of whom 4466 were male and 4954 were female, with ages ranging from 5 to 18 years. A clinical survey was conducted by the examining team in selected schools, and involved answering standard questionnaires. A total of 83 children were suspected of having heart disease. Out of these 83 children, 23 were confirmed to have heart disease; 11 had rheumatic heart disease, and 12 congenital heart disease, giving a prevalence of 1.2/1000 and 1.3/1000, respectively. The commonest cardiac lesions were mitral regurgitation in the rheumatic heart disease group, and atrial septal defect in the congenital heart disease group. A higher prevalence of congenital heart disease was detected in females., Conclusions: The prevalence of rheumatic heart disease and congenital heart disease among schoolchildren of Kathmandu is 1.2/1000 and 1.3/1000, respectively, with mitral regurgitation and atrial septal defect being the commonest lesions.

Objectives: The purpose of this study was to evaluate the rate of recognition of atrial fibrillation (AF), use of warfarin and prevalence of cerebrovascular accident (CVA) in paced versus unpaced patients during admission to a tertiary care teaching hospital., Background: The presence of AF underlying a continuously paced rhythm may be under recognized and result in a lower rate of anticoagulation and higher incidence of CVA., Methods: The identification of AF on 12 lead electrocardiogram (ECG) and telemetry, "optimal use" of anticoagulants that is, warfarin or aspirin, when warfarin is contraindicated and history of prior CVA was studied in three groups: 1) group A with continuously paced rhythm on ECG and telemetry (n = 30), 2) group B with intermittently paced rhythm on ECG and telemetry (n = 59), and 3) group C with persistent AF and no permanent pacemaker (n = 50)., Results: The identification and documentation of AF was significantly lower in the continuously paced group A (20%) versus the intermittently paced group B (44%). Both groups A and B were substantially lower than unpaced controls. "Optimal use" of anticoagulants was significantly lower in group A (40%) compared with groups B (78%) and C (72%) but was not different between groups B and C. The prevalence of prior CVA was not significantly different between the three groups., Conclusions: All ECGs in patients with paced rhythm should be examined closely for underlying AF to prevent under-recognition and under-treatment with anticoagulants.

Objective: The purpose of this study was to evaluate the value of activation mapping for radiofrequency modification of the sinus node and the long-term success rate of the procedure in a series of patients with inappropriate sinus tachycardia., Background: The results of radiofrequency ablation of inappropriate sinus tachycardia have been reported in only a small number of patients., Methods: The subjects of this study were 29 consecutive drug-refractory patients who underwent catheter ablation of inappropriate sinus tachycardia. Target sites were selected by activation mapping during sinus tachycardia., Results: The ablation procedure was successful acutely in reducing the baseline sinus rate to <90/min and the sinus rate during isoproterenol infusion by >20% in 22 of 29 patients (76%). In 13 of 22 patients (59%) with a successful acute outcome, successive applications of radiofrequency energy at the site of earliest endocardial activation resulted in a cranial-caudal migration of earliest endocardial activation from the high lateral right atrium, along with a step-wise reduction in heart rate. In the other nine patients (41%) with a successful acute outcome, the reduction in sinus rate occurred abruptly, unaccompanied by migration of the site of earliest activation. Symptoms due to inappropriate sinus tachycardia recurred at a mean of 4.4+/-; 3 months after the ablation procedure in 6 of 22 patients (27%). After additional procedures in three patients, symptoms of inappropriate sinus tachycardia ultimately were successfully eliminated over the long-term in 19 of 29 patients (66%)., Conclusions: In conclusion, radiofrequency ablation is at best only modestly effective for managing patients with inappropriate sinus tachycardia. The two different responses of heart rate to radiofrequency ablation may reflect differences in the number and/or multicentricity of subsidiary sites of impulse generation within the sinus node and/or atrium in patients with inappropriate sinus tachycardia.

Prior studies have demonstrated that sympathetic tone may influence the effects of adenosine on His-Purkinje automaticity, and that enhanced vagal tone may influence its effects on the sinus node. However, the interaction between autonomic tone and the effects of adenosine on the sinus node in humans remains unknown. Therefore, this study was designed to investigate the interaction between different states of autonomic tone and the bradycardiac response of the sinus node to adenosine. In 11 patients without structural heart disease who underwent a clinically indicated electrophysiology procedure, the sinus cycle length was measured before and after a 12-mg bolus of adenosine in the baseline state, during an infusion of 2 mcg/min of isoproterenol, after the administration of 0.2 mg/kg of propranolol, and again after the administration of 0.04 mg/kg of atropine. Adenosine significantly lengthened the sinus cycle length in the baseline state (760 +/- 165 vs 909 +/- 188 ms, P < 0.05), during isoproterenol infusion (516 +/- 67 vs 766 +/- 146 ms, P < 0.05), after propranolol (850 +/- 153 vs 914 +/- 143 ms, P < 0.05) and after the combination of propranolol and atropine (662 +/- 76 vs 801 +/- 121 ms, P < 0.05). The degree of lengthening in sinus cycle length was significantly greater (P < 0.05) during isoproterenol infusion (253 +/- 157 ms, or 51% +/- 40%) than in the baseline state (149 +/- 85 ms, or 20% +/- 12%), after propranolol (68 +/- 53 ms, or 8% +/- 8%), and after propranolol and atropine (140 +/- 110 ms, or 21% +/- 18%). The negative chronotropic effect of adenosine is influenced by autonomic tone. The effect of adenosine on the sinus node is accentuated by beta-adrenergic stimulation and unaffected by beta-adrenergic blockade or combined beta-adrenergic and cholinergic blockade.

Background: Conversion of chronic atrial fibrillation (AF) is associated with atrial stunning, but the short-term effect of a brief episode of AF on left atrial appendage (LAA) emptying velocity is unknown. The purpose of this study was to determine whether a short episode of AF affects left atrial function and whether verapamil modifies this effect., Methods and Results: The subjects of this study were 19 patients without structural heart disease undergoing an electrophysiology procedure. In 13 patients, LAA emptying velocity was measured by transesophageal echocardiography in the setting of pharmacological autonomic blockade before, during, and after a short episode of AF. During sinus rhythm, the baseline LAA emptying velocity was measured 5 times and averaged. AF was then induced by rapid right atrial pacing. After either spontaneous or electrical conversion, LAA emptying velocity was measured immediately on resumption of sinus rhythm and every minute thereafter. The mean duration of AF was 15.3+/-3.8 minutes. The mean baseline emptying velocity was 70+/-20 cm/s. The first post-AF emptying velocity was 63+/-20 cm/s (P=0.02 versus baseline emptying velocity). The post-AF emptying velocity returned to the baseline emptying velocity value after 3.0 minutes. The mean percent reduction in post-AF emptying velocity was 9.7+/-21% (range, 15% increase to 56% decrease). A second group of 6 patients were pretreated with verapamil (0.1-mg/kg IV bolus followed by an infusion of 0.005 mg. kg-1. min-1). In these patients, the first post-AF emptying velocity, 58+/-14 cm/s, was not significantly different from the pre-AF emptying velocity, 60+/-13 cm/s (P=0.08)., Conclusions: In humans, several minutes of AF may be sufficient to induce atrial contractile dysfunction after cardioversion. When atrial contractile dysfunction occurs, there is recovery of AF within several minutes. AF-induced contractile dysfunction is attenuated by verapamil and may be at least partially mediated by cellular calcium overload.

With use of transesophageal echocardiography, the short-term effects of transthoracic electrical cardioversion of atrial flutter (AFI) on atrial mechanical function and spontaneous echo contrast were determined. Thirty patients who had AFI for a mean of 6.4 +/- 12.2 months underwent transthoracic cardioversion. A transesophageal echocardiogram was recorded immediately before cardioversion, and left atrial appendage emptying velocity and spontaneous contrast were assessed serially at 1, 3, and 5 minutes after cardioversion in 28 patients, and also at 8, 10, and 15 minutes after cardioversion in a subgroup of 13 patients. Cardioversion was deferred in 2 patients (7%) because a thrombus was found in the left atrial appendage. Before cardioversion, spontaneous contrast was present in the left atrium in 7 of 28 patients (25%) who underwent cardioversion. The mean left atrial appendage emptying velocity of 54 +/- 22 cm/s before cardioversion fell by 26% to 40 +/- 25 cm/s at 1 minute after restoration of sinus rhythm (p <0.01). There were no significant changes in the mean left atrial appendage-emptying velocity between 1 and 15 minutes after cardioversion. Within 5 minutes after conversion to sinus rhythm, left atrial spontaneous echo contrast developed de novo or worsened in 12 of the 28 patients (43%). In conclusion, the results of this study demonstrate that persistent AFI may be associated with left atrial thrombi before cardioversion and that cardioversion of AFI is associated with a significant degree of atrial stunning and formation of spontaneous echo contrast.

Purpose: Adenosine is a useful agent for the diagnosis and termination of tachycardias. The purpose of this study was to identify the rhythms for which adenosine is prescribed in hospitalized adults and to identify the reasons for its misuse., Patients and Methods: Data were collected from the medical records of 100 patients who received intravenous adenosine while hospitalized at a university medical center. The characteristics of the patients, rhythms treated with adenosine, and dosages of adenosine were analyzed. In addition, internal medicine house officers were administered a questionnaire referring to an electrocardiogram of atrial fibrillation with a rapid ventricular response., Results: The arrhythmias for which adenosine was administered consisted of regular, narrow-QRS complex tachycardias in 33% of patients; atrial fibrillation in 32% of patients; regular, wide-QRS complex tachycardias in 23% of patients; atrial flutter in 10% of patients, and multifocal atrial tachycardia in 2% of patients. The mean (+/-SD) number of doses of adenosine given to each patient was 1.6+/-0.8, and the mean dose of adenosine was 7.8+/-2.8 mg. Internal medicine house officers prescribed 70% of the doses of adenosine and were as likely to use it for patients with atrial fibrillation as were surgical house officers. There was a 2% incidence of proarrhythmia, including asystole and polymorphic ventricular tachycardia. Thirty-one percent of the 100 house officers in our survey misdiagnosed a 12-lead electrocardiogram of rapid atrial fibrillation as paroxysmal supraventricular tachycardia, suggesting that adenosine may have been misused for atrial fibrillation because of errors in rhythm diagnosis. Only 5% of those who correctly diagnosed atrial fibrillation also answered that adenosine would be likely to terminate the arrhythmia, suggesting that a misunderstanding that adenosine terminates atrial fibrillation is not a common reason for its misuse., Conclusions: Approximately 40% of hospitalized adults who are treated with adenosine receive the medication unnecessarily for atrial fibrillation or atrial flutter, and this misuse results in unnecessary expenses and risks of adverse effects. The primary reason that adenosine is misused for atrial fibrillation is the inability to recognize that rhythm on an electrocardiogram. House officers need additional education on the electrocardiographic recognition of atrial fibrillation.

No prior studies have evaluated the relationship between the site of right ventricular stimulation, the site of prior infarction, and the inducibility of ventricular tachycardia (VT). This study was performed to determine if the location of pathologic Q waves influences the inducibility of VT at various right ventricular sites in patients with coronary artery disease (CAD) and a history of myocardial infarction (MI). In 30 patients with a history of sustained, monomorphic VT, CAD, prior MI, and pathologic Q waves, programmed ventricular stimulation was performed at the right ventricular apex, septum, and outflow tract, in random order. There was electrocardiographic evidence of an MI that was inferior in 11 patients, anterior in 10 patients, and both inferior and anterior in 9 patients. Sustained, monomorphic VT was induced in 27 of 30 patients (90%). There were no significant differences among the three sites in the rate of inducibility of VT. The rate of inducible VT at each of the three right ventricular sites was not affected by the location of prior infarction. In conclusion, among patients with sustained, monomorphic VT, CAD, and a history of MI, the incidence of inducible sustained, monomorphic VT is not influenced by the location of prior infarction, regardless of whether programmed ventricular stimulation is performed at the right ventricular apex, septum, or outflow tract.

Introduction: Defibrillation energy requirements in patients with nonthoracotomy defibrillators may increase within several months after implantation. However, the stability of the defibrillation energy requirement beyond 1 year has not been reported. The purpose of this study was to characterize the defibrillation energy requirement during 2 years of clinical follow-up., Methods and Results: Thirty-one consecutive patients with a biphasic nonthoracotomy defibrillation system underwent defibrillation energy requirement testing using a step-down technique (20, 15, 12, 10, 8, 6, 5, 4, 3, 2, and 1 J) during defibrillator implantation, and then 24 hours, 2 months, 1 year, and 2 years after implantation. The mean defibrillation energy requirement during these evaluations was 10.9+/-5.5 J, 12.3+/-7.3 J, 11.7+/-5.6 J, 10.2+/-4.0 J, and 11.7+/-7.4 J, respectively (P = 0.4). The defibrillation energy requirement was noted to have increased by 10 J or more after 2 years of follow-up in five patients. In one of these patients, the defibrillation energy requirement was no longer associated with an adequate safety margin, necessitating revision of the defibrillation system. There were no identifiable clinical characteristics that distinguished patients who did and did not develop a 10-J or more increase in the defibrillation energy requirement., Conclusion: The mean defibrillation energy requirement does not change significantly after 2 years of biphasic nonthoracotomy defibrillator system implantation. However, approximately 15% of patients develop a 10-J or greater elevation in the defibrillation energy requirement, and 3% may require a defibrillation system revision. Therefore, a yearly evaluation of the defibrillation energy requirement may be appropriate.

Introduction: The effect of implantable defibrillator shocks on cardiac hemodynamics is poorly understood. The purpose of this study was to test the hypothesis that ventricular defibrillator shocks adversely effect cardiac hemodynamics., Methods and Results: The cardiac index was determined by calculating the mitral valve inflow with transesophogeal Doppler during nonthoracotomy defibrillator implantation in 17 patients. The cardiac index was determined before, and immediately, 1 minute, 2 minutes, and 4 minutes after shocks were delivered during defibrillation energy requirement testing with 27- to 34-, 15-, 10-, 5-, 3-, or 1-J shocks. The cardiac index was also measured at the same time points after 27- to 34-, and 1-J shocks delivered during the baseline rhythm. The cardiac index decreased from 2.30 +/- 0.40 L/min per m2 before a 27- to 34-J shock during defibrillation energy requirement testing to 2.14 +/- 0.45 L/min per m2 immediately afterwards (P = 0.001). This effect persisted for > 4 minutes. An adverse hemodynamic effect of similar magnitude occurred after 15 J (P = 0.003) and 10-J shocks (P = 0.01), but dissipated after 4 minutes and within 2 minutes, respectively. There was a significant correlation between shock strength and the percent change in cardiac index (r = 0.3, P = 0.03). The cardiac index decreased 14% after a 27- to 34-J shock during the baseline rhythm (P < 0.0001). This effect persisted for < 4 minutes. A 1-J shock during the baseline rhythm did not effect the cardiac index., Conclusion: Defibrillator shocks > 9 J delivered during the baseline rhythm or during defibrillation energy requirement testing result in a 10% to 15% reduction in cardiac index, whereas smaller energy shocks do not affect cardiac hemodynamics. The duration and extent of the adverse effect are proportional to the shock strength. Shock strength, and not ventricular fibrillation, appears to be most responsible for this effect. Therefore, the detrimental hemodynamic effects of high-energy shocks may be avoided when low-energy defibrillation is used.

Introduction: Several studies have shown that the fast pathway is more responsive to adenosine than the slow pathway in patients with AV nodal reentrant tachycardia. Little information is available regarding the effect of adenosine on anterograde and retrograde fast pathway conduction., Methods and Results: The effects of adenosine on anterograde and retrograde fast pathway conduction were evaluated in 116 patients (mean age 47 +/- 16 years) with typical AV nodal reentrant tachycardia. Each patient received 12 mg of adenosine during ventricular pacing at a cycle length 20 msec longer than the fast pathway VA block cycle length and during sinus rhythm or atrial pacing at 20 msec longer than the fast pathway AV block cycle length. Anterograde block occurred in 98% of patients compared with retrograde fast pathway block in 62% of patients (P < 0.001). Unresponsiveness of the retrograde fast pathway to adenosine was associated with a shorter AV block cycle length (374 +/- 78 vs 333 +/- 74 msec, P < 0.01), a shorter VA block cycle length (383 +/- 121 vs 307 +/- 49 msec, P < 0.001), and a shorter VA interval during tachycardia (53 +/- 23 vs 41 +/- 17 msec, P < 0.01)., Conclusion: Although anterograde fast pathway conduction is almost always blocked by 12 mg of adenosine, retrograde fast pathway conduction is not blocked by adenosine in 38% of patients with typical AV nodal reentrant tachycardia. This indicates that the anterograde and retrograde fast pathways may be anatomically and/or functionally distinct. Unresponsiveness of VA conduction to adenosine is not a reliable indicator of an accessory pathway.

Background: The electrophysiologic effects of norepinephrine (NE) in human beings have not been previously described., Methods: The electrophysiologic effects of NE infused at a rate of 25 ng/kg/min were determined in 21 patients with a mean age of 41 +/- 11 years and without structural heart disease who underwent an electrophysiology procedure. In a subgroup of 10 patients electrophysiologic parameters were measured at baseline, after the infusion of NE, and after administration of beta-blockade while in continuous NE infusion., Results: The baseline NE plasma concentration of 298 +/- 153 pg/ml increased to 708 +/- 419 pg/ml after the infusion of NE. NE significantly increased the mean blood pressure, sinus cycle length, corrected sinus node recovery time, ventriculoatrial block cycle length, and the atrial and ventricular effective refractory periods. In a subset of 10 patients 0.2 mg/kg propranolol administered during continued infusion of NE resulted in a further increase in sinus cycle length, atrial-His interval, and ventricular refractoriness., Conclusion: A physiologic elevation in the plasma NE concentration results in a depression of sinus node function and atrioventricular conduction and in prolongation of atrial and ventricular refractoriness. Some of NE's effects are partially offset by beta-adrenergic stimulation.

Ventricular pace mapping may be used to identify the site of origin of idiopathic ventricular tachycardia. Isoproterenol is often required to induce this type of ventricular tachycardia, but its effect on QRS morphology during pace mapping is unknown. Therefore, this study was performed to evaluate the effect of isoproterenol on QRS morphology during ventricular pacing. The study population consisted of 20 patients (mean age 38 +/- 14 years) undergoing a clinically indicated electrophysiology procedure. Ventricular overdrive pacing was performed in trains of 12 stimuli at cycle lengths of 400, 350, 300, and 250 ms, first in the baseline state during an infusion of isoproterenol, and again after isoproterenol washout. Pacing was performed at the right ventricular apex in 10 patients, in the right ventricular outflow tract in 6 patients, and in the left ventricle in 4 patients. Visual evaluation revealed no apparent effects of isoproterenol on QRS morphology at any of the three pacing sites or at any of the pacing cycle lengths. It was concluded that QRS morphology during ventricular pacing is not affected by isoproterenol infusion. Therefore, in patients with idiopathic ventricular tachycardia, even if the induction of tachycardia requires infusion of isoproterenol, successful pace mapping may be performed in its absence.

Introduction: "Cardiac memory" (primary T wave change) is thought to occur after 15 minutes to several hours of right ventricular (RV) pacing. The two components of the temporal change in repolarization are memory and accumulation. The purpose of this study was to examine quantitatively the effect of short periods of ventricular pacing on the human cardiac action potential, using monophasic action potential (MAP) recordings., Methods and Results: Thirty-one patients (ages 43+/-14 years) with structurally normal hearts undergoing a clinically indicated electrophysiologic procedure were enrolled. Catheters were placed in the right atrium (RA) and RV, and a MAP catheter was positioned at the RV septum. APD90 was calculated from digitized MAP recordings. MAP morphology comparisons were performed using the root mean square (RMS) of the difference between complexes. All pacing was at 500-msec cycle length. There were four pacing protocols: (1) RA pacing was performed for approximately 15 minutes to evaluate temporal stability of the MAP recordings (5 pts); (2) to evaluate the memory phenomenon, four successive 1-minute episodes of RV pacing were interspersed with 2 minutes of RA pacing (5 pts); (3) the accumulation phenomenon was evaluated by assessing the effects of 1, 5, 10, and 15 minutes of RV pacing on the MAP during RA pacing (16 pts); and (4) 20 minutes of RV pacing was followed by 10 minutes of RA pacing to correlate visually apparent T wave changes with changes in MAP recordings (5 pts). In the control patients, no changes in APD90 or RMS analysis were noted during 14.9+/-1.4 minutes of RA pacing. In the second protocol, RMS of the difference between the baseline MAP complexes and the signal average of the first 50 beats following each of four 1-minute RV pacing trains demonstrated progressively greater differences in morphology after successive episodes of RV pacing. In protocol 3, RMS analysis identified a progressively greater difference between the baseline MAP recording and the average of the first 50 beats after 1, 5, 10, and 15 minutes of RV pacing. In protocol 4, visually apparent changes in T waves occurred in parallel with the RMS of the difference between the baseline MAP recordings and the average of the first 50 beats after 20 minutes of RV pacing. Similar changes also were demonstrated by APD90 analysis., Conclusion: This study is the first to demonstrate that episodes of abnormal ventricular activation as short as 1 minute in duration may exert lingering effects on the repolarization process once normal ventricular activation resumes.

Introduction: A variety of factors, including the number of defibrillation electrodes and shocking capacitance, may influence the defibrillation efficacy of an implantable defibrillator system. Therefore, the purpose of this study was to compare the defibrillation energy requirement using a 125 uF two-electrode defibrillation system and a 90 uF three-electrode defibrillation system., Methods and Results: The defibrillation energy requirements measured with both systems were compared in 26 consecutive patients. The two-electrode system used a single transvenous lead with two defibrillation coils in conjunction with a biphasic waveform from a 125 uF capacitor. The three-electrode system used the same transvenous lead, utilized a pectoral implantable defibrillator generator shell as a third electrode, and delivered the identical biphasic waveform from a 90 uF capacitor. The two-electrode system was associated with a higher defibrillation energy requirement (10.8 +/- 5.5 J) than was the three-electrode system (8.9 +/- 6.7 J, p < 0.05), however, the leading edge voltage was not significantly different between systems (361 +/- 103 V vs. 397 +/- 123 V, P = 0.07). The two-electrode system also had a higher shocking resistance (49.0 +/- 9.0 ohms vs. 41.4 +/- 7.3 ohms, p < 0.001) and a lower peak current (7.7 +/- 2.6 A vs. 10.1 +/- 3.7 A, p < 0.001) than the three-electrode system., Conclusions: A three-electrode defibrillation system that utilizes a dual coil transvenous lead and a subcutaneous pectoral electrode with lower capacitance is associated with a lower defibrillation energy requirement than is a dual coil defibrillation system with higher capacitance. This finding suggests that the utilization of a pectoral generator as a defibrillation electrode in conjunction with smaller capacitors is a more effective defibrillation system and may allow for additional miniaturization of implantable defibrillators.

Introduction: In patients undergoing defibrillator implantation, an appropriate defibrillation safety margin has been considered to be either 10 J or an energy equal to the defibrillation energy requirement. However, a previous clinical report suggested that a larger safety margin may be required in patients with a low defibrillation energy requirement. Therefore, the purpose of this prospective study was to compare the defibrillation efficacy of the two safety margin techniques in patients with a low defibrillation energy requirement., Methods and Results: Sixty patients who underwent implantation of a defibrillator and who had a low defibrillation energy requirement (< or = 6 J) underwent six separate inductions of ventricular fibrillation, at least 5 minutes apart. For each of the first three inductions of ventricular fibrillation, the first two shocks were equal to either the defibrillation energy requirement plus 10 J (14.6+/-1.0 J), or to twice the defibrillation energy requirement (9.9+/-2.3 J). The alternate technique was used for the subsequent three inductions of ventricular fibrillation. For each induction of ventricular fibrillation, the first shock success rate was 99.5%+/-4.3% for shocks using the defibrillation energy requirement plus 10 J, compared to 95.0%+/-17.2% for shocks at twice the defibrillation energy requirement (P = 0.02). The charge time (P < 0.0001) and the total duration of ventricular fibrillation (P < 0.0001) were each approximately 1 second longer with the defibrillation energy requirement plus 10 J technique., Conclusion: This study is the first to compare prospectively the defibrillation efficacy of two defibrillation safety margins. In patients with a defibrillation energy requirement < or = 6 J, a higher rate of successful defibrillation is achieved with a safety margin of 10 J than with a safety margin equal to the defibrillation energy requirement.

Background: Atrial fibrillation occurs commonly after open-heart surgery and may delay hospital discharge. The purpose of this study was to assess the use of preoperative amiodarone as prophylaxis against atrial fibrillation after cardiac surgery., Methods: In this double-blind, randomized study, 124 patients were given either oral amiodarone (64 patients) or placebo (60 patients) for a minimum of seven days before elective cardiac surgery. Therapy consisted of 600 mg of amiodarone per day for seven days, then 200 mg per day until the day of discharge from the hospital. The mean (+/-SD) preoperative total dose of amiodarone was 4.8+/-0.96 g over a period of 13+/-7 days., Results: Postoperative atrial fibrillation occurred in 16 of the 64 patients in the amiodarone group (25 percent) and 32 of the 60 patients in the placebo group (53 percent) (P=0.003). Patients in the amiodarone group were hospitalized for significantly fewer days than were patients in the placebo group (6.5+/-2.6 vs. 7.9+/-4.3 days, P=0.04). Nonfatal postoperative complications occurred in eight amiodarone-treated patients (12 percent) and in six patients receiving placebo (10 percent, P=0.78). Fatal postoperative complications occurred in three patients who received amiodarone (5 percent) and in two who received placebo (3 percent, P= 1.00). Total hospitalization costs were significantly less for the amiodarone group than for the placebo group ($18,375+/-$13,863 vs. $26,491+/-$23,837, P=0.03)., Conclusions: Preoperative oral amiodarone in patients undergoing complex cardiac surgery is well tolerated and significantly reduces the incidence of postoperative atrial fibrillation and the duration and cost of hospitalization.

Four of 12 patients (33%) with paroxysmal supraventricular tachycardia (PSVT) and tachycardia-induced atrial fibrillation (AF) had recurrences of paroxysmal AF after successful catheter ablation of the PSVT. This study demonstrates that AF often remains a problem after radiofrequency catheter ablation of PSVT in patients with tachycardia-induced AF, and it may not be possible to predict in which patients this will be the case.

In a retrospective analysis of patients referred for atrioventricular node radiofrequency ablation, male gender and a history of hypertension were found to be predictors of crossover to a left ventricular approach for success. This subgroup of patients may benefit from early crossover if initial attempts at right-sided ablation fail.

Temperature monitoring may be helpful for ablation of accessory pathways, however its role in ablation of atrioventricular nodal reentrant tachycardia (AVNRT) using the slow pathway approach is unclear. Therefore, the purpose of this study was to prospectively compare slow pathway ablation for AVNRT using fixed power or temperature monitoring. The study included 120 patients undergoing ablation for AVNRT. Patients were randomly assigned to receive either fixed power at 32 watts, or to temperature monitoring with a target temperature of 60 degrees C. The primary success rate was 72% in the fixed power group and 95% in the temperature monitoring group (p = 0.001). The ablation procedure duration (35 +/- 29 min vs 35 +/- 30 min; p = 0.9), fluoroscopic time (32 +/- 17 vs 35 +/- 19 min; p = 0.4), mean number of applications (10.2 +/- 8.1 vs 8.4 +/- 7.9; p = 0.2), and coagulum formation per application (0.2% vs 0.5%; p = 0.6) were statistically similar in the fixed power and temperature monitoring groups, respectively. The mean temperature (47.3 +/- 4.8 degrees C vs 48.6 +/- 3.8 degrees C; p < 0.01), and the temperature associated with junctional ectopy (48.2 +/- 3.8 degrees C vs 49.3 +/- 3.6 degrees C, p < 0.01) were less for the fixed power than the temperature monitoring group. In the temperature monitoring group, only 31% of applications achieved an electrode temperature of 60 degrees C. During follow up of 6.6 +/- 3.6 months there were two recurrences in the fixed power group and one in the temperature monitoring group (p = 1.0). In summary, power titration directed by temperature monitoring was associated with an improved primary procedural success rate. Applications of energy were associated with a temperature of approximately 50 degrees C with both techniques, suggesting that there is a low efficiency of heating in the posterior septum.

Background: Adenosine is considered safe and effective for paroxysmal supraventricular tachycardia (PSVT), but anecdotal experience suggests that adenosine can precipitate atrial arrhythmias., Objectives: To determine the frequency and mechanisms of adenosine-induced atrial arrhythmias., Setting: Clinical electrophysiology laboratory at a university medical center., Design: Prospective observational study., Patients: 200 consecutive patients with PSVT undergoing an electrophysiology procedure., Intervention: During PSVT, 12 mg of adenosine was administered centrally through the femoral vein., Measurements: Frequency of adenosine-induced atrial fibrillation., Results: Paroxysmal supraventricular tachycardia terminated after adenosine administration in 198 patients (99% [95% CI, 96% to 100%]). Adenosine led to atrial fibrillation (n = 22) or atrial fibrillation and atrial flutter (n = 2) in 24 patients (12% [CI, 7.5% to 16.5%]). An atrial premature complex occurred in all 24 patients who developed atrial fibrillation, atrial flutter, or both and in 102 of the 176 patients (58%) who did not (P < 0.001). The mean (+/-SD) time from the preceding atrial complex to the atrial premature complex was shorter when an atrial arrhythmia occurred, and the mean ratio of this interval to the preceding atrial cycle length was also lower when atrial fibrillation developed (0.37 +/- 0.16 compared with 0.49 +/- 0.16; P = 0.002)., Conclusions: The incidence of atrial fibrillation induced by 12 mg of adenosine administered through the femoral vein was 12%. Fibrillation seems to be associated with a "long-short" atrial sequence. If the mechanism of PSVT is unknown and the Wolff-Parkinson-White syndrome is possible, administration of adenosine should be limited to medical facilities that have emergency resuscitation equipment.

Background: Implantable cardioverter-defibrillator (ICD) therapy is integral to current therapy for ventricular tachycardia. Patients with an ICD frequently require concomitant antiarrhythmic drug therapy. Despite this, some patients still receive frequent ICD therapies for ventricular tachycardia. Therefore, the purpose of this prospective study was to determine the utility of ablation of ventricular tachycardia in patients with an ICD who experience frequent ICD therapies., Methods and Results: Twenty-one consecutive patients with frequent ICD therapies despite antiarrhythmic drug therapy were the subjects of this study. The mean age was 69+/-6 years, and 17 were men. The mean ejection fraction was 0.22+/-0.08, and all patients had coronary artery disease. During the 36+/-51 days (range, 4 days to 7 months) preceding the ablation procedures, the patients received 34+/-55 ICD therapies for the clinical ventricular tachycardia, or a mean of 25+/-88 ICD therapies per month. The patients underwent radiofrequency ablation of the presumed clinical ventricular tachycardia by inducing the tachycardia and mapping according to endocardial activation, continuous electrical activity, pace mapping, concealed entrainment, or mid-diastolic potentials. Ablation of the clinical arrhythmia was successful in 76% of patients during 1.4+/-0.6 (range, 1 to 3) ablation procedures and required 12.5+/-9.2 applications of energy. During 11.8+/-10.0 months of follow-up, the frequency of ICD therapies per month decreased from 60+/-80 before successful ablation to 0.1+/-0.3 ICD therapies per month after ablation (P=.01). A quality-of-life assessment demonstrated a significant improvement after successful (P=.02) but not unsuccessful ablation (P=.9)., Conclusions: Radiofrequency ablation of ventricular tachycardia as adjuvant therapy in patients with coronary artery disease and an ICD has a reasonable success rate, significantly reduces ICD therapies, and appears to be associated with an improved quality of life.

Background: Atrial fibrillation (AF) shortens the atrial effective refractory period (ERP) and predisposes to further episodes of AF. The purpose of this study was to determine the effect of verapamil and procainamide on these manifestations of AF-induced electrical remodeling., Methods and Results: In adult patients without structural heart disease, the atrial ERP was measured before and after AF after pharmacological autonomic blockade and administration of verapamil (17 patients), procainamide (10 patients), or saline (20 patients). AF was then induced by rapid pacing. Immediately on AF conversion, the post-AF ERP was measured at alternating drive cycle lengths of 350 and 500 ms. In the saline group, the pre-AF and first post-AF ERPs at the 350-ms drive cycle length were 206+/-19 and 179+/-27 ms (P<.0001), respectively, and at the 500-ms drive cycle length, the values were 217+/-16 and 183+/-23 ms, respectively (P<.0001). There was a similar significant shortening of the first post-AF ERP in the procainamide group. In the verapamil group, however, there was no difference between the pre-AF and the first post-AF ERP at the 350-ms (226+/-15 versus 227+/-22 ms, P=.8) or 500-ms (230+/-17 versus 232+/-20 ms, P=.6) drive cycle length. During determinations of the post-AF ERP, 105 secondary episodes of AF were unintentionally induced in 12% of verapamil patients compared with 90% and 80% of saline and procainamide patients (P<.01 versus verapamil)., Conclusions: Pretreatment with the calcium channel antagonist verapamil, but not the sodium channel antagonist procainamide, markedly attenuates acute, AF-induced changes in atrial electrophysiological properties. These data suggest that calcium loading during AF may be at least partially responsible for AF-induced electrical remodeling.

Background: Because it is not clear which technique is less expensive, the purpose of this study was to compare the cost of radiofrequency modification and ablation of the atrioventricular (AV) node in drug-refractory patients with atrial fibrillation and an uncontrolled ventricular rate., Methods and Results: The initial nominal charges for a successful procedure were compared in 10 patients with chronic atrial fibrillation who underwent modification of the AV node ($13 109+/-2002) and 14 similar patients who underwent ablation and pacemaker implantation ($28 302+/-2023, P<.001). On the basis of the long-term follow-up of patients who underwent each procedure, it was assumed that 31% of patients selected for the modification procedure would require a permanent pacemaker for inadvertent AV block or because of AV nodal ablation after a failed modification procedure and that the recurrence rate after AV node ablation would be 2%. The annual charges during follow-up were predicted and adjusted for recurrences and the need for additional procedures. The adjusted total charges at 1 year of follow-up were significantly lower for the modification procedure ($19 389+/-2002) than for the ablation procedure ($28 485+/-2023, P<.001). After 10 years of follow-up, the cumulative, adjusted charges for modification were $20 016 (42%) less than for ablation., Conclusions: The initial charges generated by AV node modification are significantly lower than for AV node ablation in patients with chronic atrial fibrillation. Even when adjusted for higher failure and recurrence rates, the modification procedure retains a major cost advantage over ablation during long-term follow-up.

Introduction: The purpose of this study was to determine the accuracy of the unipolar electrogram for identifying the earliest site of ventricular activation. The earliest site of ventricular activation may be identified with the unipolar electrogram by the absence of an R wave. However, the accuracy of this technique is unknown., Methods and Results: A single ventricular premature complex was induced mechanically at the tip of an electrode catheter to simulate a ventricular premature depolarization site of origin. Unipolar electrograms were recorded from the right ventricular septum at the tip electrode and at 2, 5, 8, and 11 mm from the electrode tip in 20 patients. No R waves were detected at the ventricular premature depolarization site of origin. R waves were detected in 4 of 20 patients (20%) at 2 mm from the tip electrode and 7 of 20 patients (35%) at 5, 8, and 11 mm from the tip electrode. An R wave was not observed at distances < or = 11 mm from the site of tachycardia origin in 13 of 20 patients (65%)., Conclusions: While an R wave in the unipolar electrogram can be seen as close as 2 mm from the site of impulse origin, the absence of an R wave as an indicator of the site of impulse origin in the right ventricle is highly inaccurate. Therefore, the absence of an R wave in the unipolar electrogram is unlikely to be an adequate guide for identification of an effective target site for ablation of right ventricular tachycardia.

Background: The probability of successful defibrillation has been determined in normal animals but not in patients undergoing defibrillator implantation. Therefore, the purpose of this prospective study was to determine the probability of successful defibrillation in humans on the basis of a step-down defibrillation energy requirement., Methods and Results: Fifty-three consecutive patients underwent five separate inductions of ventricular fibrillation after the defibrillation energy requirement was determined with the use of small decrements and a step-down protocol (20, 15, 12, 10, 8, 6, 5, 4, 3, 2, 1, and 0.8 J). The first shock energy for defibrillation was either 1.0, 1.3, 1.5, 1.7, or 2.0 times the defibrillation energy requirement, and the likelihoods of successful defibrillation were 70+/-27%, 84+/-12%, 86+/-25%, 80+/-29%, and 88+/-32%, respectively (P=.03). The frequencies of uniformly successful defibrillation (5 of 5 defibrillation attempts) were 30%, 27%, 60%, 64%, and 73%, respectively (P=.01). Seven patients in whom the defibrillation energy requirement was <4 J had an overall rate of successful defibrillation of 54+/-20% compared with 86+/-20% in the remaining 47 patients (P=.002). The likelihood of successful defibrillation at twice the defibrillation energy requirement was 98% in the 46 patients with a defibrillation energy requirement of >4 J and 67% in the 7 patients with a defibrillation energy requirement of <4 J (P=.17). An absolute safety margin of 7 J was associated with a 96% probability of successful defibrillation., Conclusions: The probability of successful defibrillation is 70% at the defibrillation energy requirement. The probability plateaus at 88%, at twice the defibrillation energy requirement. A 96% probability of successful defibrillation is achieved at an absolute safety margin of 7 J, and a 98% success rate is achieved at energies that are twice the defibrillation energy requirement if the defibrillation energy requirement is >4 J. If the defibrillation energy requirement is <4 J, larger multiples of the defibrillation energy requirement are needed to achieve a high probability of successful defibrillation.

Objectives: The goal of this study was to determine whether isolated diastolic potentials (IDPs) recorded during ventricular tachycardia (VT) are generated in zones of slow conduction and whether the arcs of block that bound these zones of slow conduction are functional or anatomic in nature., Background: No previous studies have systematically investigated the response to pacing during VT and sinus rhythm at sites where IDPs are recorded., Methods: The study included 11 patients with a previous infarction who underwent radiofrequency catheter ablation of 15 hemodynamically stable, sustained VTs and in whom an IDP that could not be dissociated from the VT was detected during mapping., Results: Pacing during VT at the site where the IDP was recorded resulted in concealed entrainment in each of the 15 VTs. In 10 of the 15 VTs, an IDP was present during sinus rhythm at the same site at which a diastolic potential was recorded during VT. In nine VTs, the isolated potential occurred early in diastole; in these cases, the QRS configuration during pacing in the setting of sinus rhythm was different from that during VT. In six VTs, the isolated potential occurred later in diastole, and in these cases, the QRS configuration during pacing in the setting of sinus rhythm was the same as that during VT., Conclusions: Isolated diastolic potentials may often be generated in an area of slow conduction bounded by arcs of block that are anatomically determined and present during sinus rhythm.

This study determined the efficacy of single- and multisite atrial pacing for terminating episodes of atrial fibrillation induced in patients in the electrophysiology laboratory. One- to 5-second bursts of atrial pacing at a cycle length of 20 ms were not effective in terminating atrial fibrillation, when delivered either in the high right atrium or when delivered simultaneously at the high right atrium, midseptum, and coronary sinus.

Introduction: Idiopathic left ventricular tachycardia typically has a right bundle branch block configuration. The purpose of this case report is to demonstrate that idiopathic ventricular tachycardia arising in or near the left posterior fascicle also may have a left bundle branch block configuration., Methods and Results: A 27-year-old woman underwent an electrophysiologic procedure because of recurrent, verapamil-responsive, wide QRS complex tachycardia. Two types of ventricular tachycardia (cycle lengths 330 to 340 msec) were reproducibly inducible, one with a right bundle branch block configuration and left-axis deviation that had been documented clinically, and the other with a left bundle branch block configuration and axis of zero. A Purkinje potential recorded at the junction of the left ventricular mid-septum and inferior wall preceded the ventricular complex by 40 msec in both tachycardias. A single application of radiofrequency energy at this site successfully ablated both ventricular tachycardias., Conclusion: The findings of this case report demonstrate that idiopathic ventricular tachycardia arising in or near the left posterior fascicle may have a left bundle branch block configuration.

This study demonstrates that shocks <200 J often are effective for transthoracic cardioversion of atrial fibrillation (AF). Lower energy shocks are more likely to be effective when the AF is <24 hours in duration or in patients with idiopathic AF.

The chronic defibrillation energy requirement (DER) is believed to remain clinically stable in patients with defibrillators. Six patients (two with an epicardial and four with a nonthoracotomy system) were identified with a rise in their chronic DER, which eliminated a 10-J safety margin, thus necessitating a defibrillator lead system revision. The mean increase in DER was 14.7 +/- 4 J and was discovered at a mean of 16.0 +/- 18 months (range 2-41) following implantation. Management included placement of a defibrillator with a biphasic waveform, placement of an additional defibrillation electrode, or both. At 2 months following revision of the defibrillation system, a 10-J DER safety margin was present in each patient. In some patients, there is a progressive increase in the chronic DER with elimination of a 10-J safety margin necessitating revision of the defibrillation system. Routine reevaluation of the chronic DER, therefore, is necessary to identify these patients.

Background: Concealed entrainment has been useful in guiding catheter ablation of monomorphic ventricular tachycardia in patients with coronary artery disease. However, not all sites with concealed entrainment result in successful ablation of the targeted ventricular tachycardia. The purpose of this prospective study was to identify factors at sites that demonstrate concealed entrainment that differentiate effective from ineffective target sites., Methods and Results: In 14 consecutive patients with hemodynamically stable monomorphic ventricular tachycardia and coronary artery disease, radiofrequency ablation of 26 ventricular tachycardias was performed. Ablation was attempted at 46 sites that demonstrated concealed entrainment. Twenty-five of the targeted ventricular tachycardias (96%) were successfully ablated. The positive predictive value of concealed entrainment for successful ablation was 54%; it increased to 72% in the presence of a stimulus-QRS interval/ventricular tachycardia cycle length ratio of < or = 70%, to 82% in the presence of a match of the stimulus-QRS and electrogram-QRS interval, and to 89% in the presence of isolated mid diastolic potentials that could not be dissociated from ventricular tachycardia during entrainment., Conclusions: The positive predictive value of concealed entrainment for identification of successful ablation sites in patients with sustained ventricular tachycardia and coronary artery disease can be significantly enhanced by the presence of associated mapping criteria, particularly an isolated mid diastolic potential that cannot be dissociated from the tachycardia.

The main finding of this prospective, controlled study is that amiodarone and desethylamiodarone plasma concentrations < 1 mg/L are associated with a 23% increase in the acute defibrillation energy requirement and with a 31% increase in the requirement for a subcutaneous patch or array. The defibrillation energy requirement does not correlate with the plasma concentrations of amiodarone, desethylamiodarone, amiodarone plus desethylamiodarone, or with the duration or daily dosage of amiodarone therapy.

Objectives: The purpose of this study was to describe the long-term follow-up results in 62 patients with atrial fibrillation and an uncontrolled ventricular rate, who underwent radiofrequency modification of the atrioventricular (AV) node., Background: Previous studies in small numbers of patients have suggested that radiofrequency modification may be effective in controlling the ventricular rate in patients with atrial fibrillation, but long-term follow-up data have been lacking., Methods: The subjects of this study were 62 consecutive patients (mean age +/- SD 65 +/- 14 years; 43 with structural heart disease) who underwent an attempt at radiofrequency modification of the AV node because of symptomatic, drug-refractory atrial fibrillation with an uncontrolled ventricular rate. The atrial fibrillation was chronic in 46 patients and paroxysmal in 16. Radiofrequency energy was applied to the posteroseptal or mid-septal right atrium to lower the ventricular rate in atrial fibrillation to 120 to 130 beats/min during an infusion of 4 micrograms/min of isoproterenol., Results: Short-term control of the ventricular rate was successfully achieved without the induction of pathologic AV block in 50 (81%) of 62 patients. Inadvertent high degree AV block occurred in 10 (16%) of 62 patients, with the AV block occurring at the time of the procedure in 6 patients and 36 to 72 h after the procedure in 4. During 19 +/- 8 months of follow-up (range 4 to 33), 5 (10%) of 50 patients had a symptomatic recurrence of an uncontrolled rate during atrial fibrillation. Overall, adequate rate control at rest and during exertion, without pathologic AV block, was achieved long term in 45 (73%) of 62 patients. Among 37 patients with a successful outcome, left ventricular ejection fraction increased from (mean +/- SD) 0.44 +/- 0.14 to 0.51 +/- 0.10 one year later (p < 0.001). Complications other than AV block included polymorphic ventricular tachycardia 10 to 24 h after the procedure in two patients who had a predisposing factor for ventricular tachycardia and sudden death 1 to 5 months after the procedure in two patients with idiopathic dilated cardiomyopathy, one of whom had a pacemaker for AV block., Conclusions: In approximately 70% of properly selected patients with atrial fibrillation and an uncontrolled ventricular rate, radiofrequency modification of the AV node results in excellent long-term control of the ventricular rate at rest and during exertion.

Impairment of cardiac function in atrial fibrillation has been attributed to loss of atrial contraction and to a rapid ventricular rate. The results of this study suggest that irregularity of the ventricular rhythm, independent of the ventricular rate, may also contribute to impairment of cardiac function during atrial fibrillation.

Objectives: The purpose of this study was to determine the incidence and to clarify the mechanism of 2:1 atrioventricular (AV) block during AV node reentrant tachycardia induced in the electrophysiology laboratory., Background: In patients with 2:1 AV block during AV node reentrant tachycardia, the absence of a His bundle potential in the blocked beats has been considered evidence of intranodal, lower common pathway block., Methods: In consecutive patients with AV node reentrant tachycardia, the incidence of 2:1 AV block and the response to atropine and a single ventricular extrastimulus was observed., Results: Persistent 2:1 AV block occurred in 13 of 139 patients with AV node reentrant tachycardia. A His bundle deflection was present in the blocked beats in eight patients and absent in five. Patients with 2:1 AV block had a shorter tachycardia cycle length than did patients without such block (mean +/- SD 312 +/- 32 vs. 353 +/- 55 ms, p < 0.01). Atropine did not alter the 2:1 block in any patient. In every patient, a single ventricular extrastimulus introduced during the tachycardia converted the 2:1 block to 1:1 conduction., Conclusions: The incidence of induced 2:1 AV block during AV node reentrant tachycardia is approximately 10%. The lack of a response to atropine and the consistent conversion of 2:1 block to 1:1 conduction by a ventricular extrastimulus indicate that, regardless of the presence or absence of a His bundle potential in blocked beats, 2:1 block during AV node reentrant tachycardia is due to functional infranodal block.

Background: Ventricular pace mapping is performed by comparing the QRS morphology of ventricular paced complexes to that of a template arrhythmia, either a premature ventricular depolarization or a QRS complex during ventricular tachycardia. The objective of this study was to evaluate the effect of coupling interval and pacing cycle length on QRS morphology., Methods and Results: The study population consisted of 20 patients (mean age, 38 +/- 16 years) undergoing a clinically indicated electrophysiology procedure. In the first 10 patients, the effect of coupling interval on the morphology of single paced ventricular complexes was evaluated visually and by signal processing techniques. Visually apparent differences in QRS morphology occurred in a mean of 4/12 electrocardiographic leads with a change in coupling interval of > or = 100 ms. In the next 10 patients, the QRS complex morphology during ventricular overdrive pacing at cycle lengths of 600 and 300 ms was found to differ significantly in a mean of 4/12 leads. The QRS morphology during overdrive pacing differed significantly from that of a single paced complex whenever the pacing cycle length differed from the coupling interval of the single paced complex by > 80 ms., Conclusions: The morphology of single paced QRS complexes may vary, depending on coupling interval, and the QRS morphology during overdrive pacing is affected by the pacing cycle length. During ventricular pace mapping, the coupling interval or cycle length of the template arrhythmia should be matched during pacing. If not, rate-dependent changes in QRS morphology that are independent of the pacing site may confound the results of pace mapping.

Atrioventricular nodal reentrant tachycardia and accessory pathway-mediated tachycardia may have different ages of tachycardia onset. Symptom onset data were obtained in 519 patients (atrioventricular nodal reentrant tachycardia, 231, accessory pathway-mediated tachycardia, 288). The mean age of the patients at the time of evaluation was 47 +/- 17 years (atrioventricular nodal reentrant tachycardia) and 37 +/- 15 years (accessory pathway-mediated tachycardia). The mean age of symptom onset was 32 +/- 18 years for atrioventricular nodal reentrant tachycardia and 23 +/- 14 years for accessory pathway-mediated tachycardia. A significantly greater proportion of patients with atrioventricular nodal reentrant tachycardia had the initial onset of symptoms after the age of 20 years (atrioventricular nodal reentrant tachycardia, 67% vs accessory pathway-mediated tachycardia, 41%, p < 0.001). In summary, there is a different mean age of symptom onset for patients with atrioventricular nodal reentrant tachycardia and accessory pathway-mediated tachycardia.

The purpose of this study was to compare the atrial-His intervals generated during programmed atrial stimulation in patients with and without dual atrioventricular nodal physiology and with and without inducible atrioventricular nodal reentrant tachycardia. Programmed atrial stimulation at a basic-drive cycle length of 500 to 600 msec was performed in 180 patients. The minimum atrial-His interval was defined as the atrial-His interval of the basic-drive beats. The maximum atrial-His interval was defined as the longest A2H2 interval. The criterion for dual atrioventricular nodal physiology was an increment of 50 msec in the A2H2 interval in association with a 10 msec decrement in the A1A2 interval. The minimum atrial-His interval was significantly shorter (106 +/- 34 msec vs 116 +/- 29 msec; p < 0.05) and the maximum atrial-His interval significantly longer (304 +/- 101 msec vs 222 +/- 56 msec; p < 0.001) in the 87 patients who had atrioventricular nodal reentry than in the 93 patients who did not. Among the 87 patients who had atrioventricular nodal reentry, the maximum atrial-His interval was significantly longer in 53 patients who had dual atrioventricular nodal physiology than in 34 patients who did not (340 +/- 105 msec vs 249 +/- 62 msec; p < 0.001). Among the 66 patients who had dual atrioventricular nodal physiology, the maximum atrial-His interval was significantly longer in 53 patients who had atrioventricular nodal reentry than in 13 patients who did not (340 +/- 105 msec vs 268 +/- 61 msec; p < 0.01). The insensitivity of the conventional dual atrioventricular nodal physiology criterion for the detection of dual atrioventricular nodal pathways is in part attributable to a lesser degree of slowing of conduction in the slow pathway relative to the fast pathway in some patients who have atrioventricular nodal reentry. The inability to demonstrate atrioventricular nodal reentry despite the presence of dual atrioventricular nodal physiology in some persons may be attributable in part to an inadequate degree of conduction delay in the slow pathway.

Objectives: The purpose of this study was to assess the clinical efficacy of radiofrequency ablation of the slow pathway in patients with documented but noninducible paroxysmal supraventricular tachycardia (PSVT) who have evidence of dual atrioventricular (AV) node pathways., Background: Patients with a documented history of PSVT at times do not have inducible PSVT in the electrophysiology laboratory. Because dual AV node pathways serve as the substrate for AV node reentrant tachycardia (AVNRT), ablation of the slow pathway potentially may be useful in these patients., Methods: The subjects in this prospective study were seven consecutive patients who underwent an electrophysiologic procedure because of documented PSVT and were found to have dual AV node physiology or inducible single AV node echo beats, but no inducible PSVT despite the administration of isoproterenol and atropine. Their mean (+/- SD) age was 33 +/- 13 years, and they had been symptomatic for 12 +/- 12 years. The frequency of the episodes of PSVT ranged from > or = 1/day to 1/month. The rate of the documented episodes ranged from 170 to 260 beats/min, and discrete P waves were not apparent. Slow pathway ablation was performed with 9 +/- 4 applications of radiofrequency energy using a combined anatomic and electrogram mapping approach., Results: All evidence of dual AV node pathways was eliminated in six patients, and dual AV node physiology remained present in one patient. During a mean follow-up period of 15 +/- 10 months (range 8 to 27), no patient had a recurrence of symptomatic tachycardia (success rate 95% confidence interval 65% to 100%)., Conclusions: Slow pathway ablation may be clinically useful in patients with documented but noinducible PSVT who have evidence of dual AV node pathways.

Background: The acute effect of atrial fibrillation (AF) on the atrial effective refractory period (ERP) in humans is unknown., Methods and Results: In 20 patients without structural heart disease, the atrial ERP was measured before and after pacing-induced AF at drive cycle lengths of 350 and 500 ms. Immediately after spontaneous AF conversion, the post-AF ERP was measured. The pre-AF ERPs at 350 and 500 ms were 206 +/- 23 and 216 +/- 17 ms, respectively. The time to spontaneous conversion of AF was 7.3 +/- 1.9 minutes. The first post-AF ERPs at drive cycle lengths of 350 and 500 ms were 175 +/- 30 ms (P < .0001 versus pre-AF) and 191 +/- 30 ms (P < .0001 versus pre-AF), respectively. The post-AF ERP returned to the pre-AF ERP value after a mean of 8.4 +/- 0.3 minutes. In 15 patients, during the determination of the post-AF ERP, secondary episodes of AF lasting 1 +/- 1.5 minutes were reinduced 6 +/- 3 times per patient. There was a significant inverse logarithmic relationship between the time to reinduction of AF and the duration of secondary episodes of AF (P < .0001, r = 5)., Conclusions: In humans, several minutes of induced AF is sufficient to shorten the ERP for up to approximately 8 minutes. The temporal recovery of the ERP is reflected in progressively shorter episodes of reinduced AF. These data imply that AF transiently shortens the atrial wavelength and suggest a mechanism by which AF may perpetuate itself.

Background: The purpose of this study was to examine the spatial resolution of unipolar atrial pace mapping by pacing at adjacent sites within the coronary sinus and the right atrium., Methods and Results: Unipolar pacing from each pole of a quadripolar catheter was performed in the coronary sinus (n = 29) and in the right atrium (n = 10). Pacing from the distal electrode was used to simulate the site of origin of an atrial tachycardia. These P waves were compared with the P waves generated by unipolar pacing from each of the three proximal electrodes. The P waves were analyzed for changes in amplitude, duration, and configuration. Pacing within the coronary sinus resulted in significant changes in amplitude and duration at distances of 17 and 21 mm from the distal pole, respectively. Similarly, pacing in the right atrium resulted in significant changes in amplitude and duration at distances of 17 and 32 mm from the distal pole, respectively. No significant changes in configuration were noted in the coronary sinus in any lead at packing sites < or = 32 mm from the distal pole. Configurational changes were noted in the right atrium at pacing sites 17 mm from the distal pole., Conclusions: The spatial resolution of unipolar atrial pace mapping is approximately 17 mm. These findings indicate that mapping techniques that depend on the accurate discrimination of P-wave morphology, such as pace mapping or concealed entertainment, are likely to be imprecise when used in the atria.