Search

Background: Limited medical options are available for rhythm control in patients with atrial fibrillation (AF) and hypertrophic cardiomyopathy (HCM). There are no published reports of dofetilide use in this population., Methods: A retrospective chart review was conducted on 1,404 patients loaded on dofetilide for AF suppression at the Cleveland Clinic from 2008 to 2012, 25 of whom were found to have HCM., Results: The HCM cohort was 32% female, 76% with persistent AF, mean age of 59 ± 10 years, and mean ejection fraction of 54 ± 9 %. Of the 25 patients, 21 were discharged on dofetilide, three discontinued during loading due to QTc prolongation, and one due to inefficacy. There were no adverse events during loading. Of those discharged on dofetilide, 11/21 (52%) were still on it at a median follow-up of 396 (198, 699) days at the time of the chart review. For those in whom it was discontinued, the median time on the drug was 301 (111, 738) days. Of the 10 patients who discontinued dofetilide during follow-up, six were due to inefficacy, one postablation, one postheart transplant, one due to death secondary to lung cancer, and one due to worsening edema., Conclusions: Dofetilide was well tolerated in this group of patients with AF and HCM and it facilitated management of AF in 21/25 (84%) patients. Further research is needed to assess the safety and efficacy of dofetilide in order to develop evidence-based guidelines for the pharmacological management of AF in this population., (© 2018 Wiley Periodicals, Inc.)

Background: Unnecessary ventricular pacing from cardiac implantable electronic devices has been associated with long-term risks (heart failure, atrial fibrillation, and possibly stroke). Several device programming strategies are available to minimize ventricular pacing, each potentially associated with unintended consequences. Occasionally, the only effective means is to program to the AAI(R) pacing mode. However, in one manufacturer's implantable cardioverter defibrillators (ICDs), the AAI(R) mode has the potential risk of prolonged pacing cessation following a nonsustained ventricular tachycardia (NSVT)., Method: Patients with ICDs, managed through the Cleveland Clinic device clinic, follow the Heart Rhythm Society consensus document recommendations for device monitoring with remote interrogations (every three months) and yearly in-person evaluations. Clinically significant findings also trigger additional evaluations by the nurse and physician., Results: Two patients having Boston Scientific ICDs (E110 Teligen 100; Boston Scientific Corp., Natick, MA, USA), had asystole and marked bradycardia following untreated NSVT. These pauses in pacing were due to use of the AAI(R) pacing mode. In order to enhance ventricular tachycardia detection, by design atrial pacing is disabled during, and for a time after, an episode of ventricular tachycardia when the device operates in the "ventricular tachycardia response" (VTR) phase. Thus, following spontaneous termination of the NSVT, no pacing occurred in these patients until the VTR period ended. Nonconventional programming was utilized to permit AAI(R) pacing while avoiding these asystolic and bradycardic events during VTR., Conclusions: Unintended consequences can occur when complex VT detection parameters interact with specific pacing modes. At times, nonconventional programming can avoid these interactions while still achieving effective AAI(R) pacing., (© 2015 Wiley Periodicals, Inc.)

Background: Many patients eligible for cardiac resynchronization therapy (CRT) are over 80 years of age. Survival in this population and how it compares to the general octogenarian population has not been established., Methods: We extracted clinical data on a cohort of 800 consecutive patients undergoing the new implantation of a CRT device between April 15, 2004 and August 6, 2007. Patients over age 80, with class III-IV New York Heart Association heart failure symptoms on optimal medical therapy undergoing initial CRT implantation, were included in the final cohort. Using the United States Social Security Period Life Table for 2006, fractional survival for octogenarians in the general population was calculated and matched to our cohort based on age and gender. A comparison was then made between octogenarians undergoing CRT compared to the general population., Results: A total of 95 octogenarians who met inclusion criteria were identified, of whom 86.3% received a biventricular defibrillator and the remainder a biventricular pacemaker. Over a mean follow-up of 3.6 ± 1.5 years, there were 47 deaths (47.4%). The mean survival time was 4.1 years (95% CI 3.7-4.5), and survival at 2 years was 78.9%. Compared to the general octogenarian population, octogenarians receiving CRT had only modestly worse survival over the duration of follow-up with the survival curves diverging at 2 years of follow-up (P = 0.03)., Conclusions: Octogenarians with advanced heart failure have a reasonable mean survival time following CRT. All-cause mortality in this patient population is only modestly worse compared to the general octogenarian population. Therefore, in octogenarians deemed to be reasonable candidates, CRT should not be withheld based on age alone., (©2014 Wiley Periodicals, Inc.)

Background: Following pulmonary vein isolation (PVI) for the treatment of paroxysmal atrial fibrillation (AF), spontaneous dissociated firing (DiFi) from the isolated veins may be observed. Little is known about the significance and prognostic implications of this phenomenon. We sought to determine the relationship between DiFi and ablation outcomes., Methods: The study population consisted of 156 paroxysmal AF patients who underwent first time PVI and were found to have spontaneous DiFi from the pulmonary veins (PVs). Their outcomes were compared to a population of 156 propensity-matched controls from our prospectively maintained AF ablation data registry., Results: DiFi was most frequently observed from the right superior PV and occurred in 89 patients (57.1%). After 24 months of follow-up, patients with DiFi had better success rates compared to those with silent veins after isolation (88.5% vs 75%, P = 0.002). The overall distribution of types of recurrent arrhythmia was similar between DiFi patients and their matched controls (P = NS). During repeat ablations, DiFi patients were less likely to have PV conduction recovery (60% vs 93.3%, P = 0.02). Importantly, none of the veins with DiFi during index procedures was found to have conduction recovery., Conclusion: In patients with paroxysmal AF undergoing ablation, DiFi from the PVs after their isolation was associated with improved ablation outcomes. It is possible that DiFi is an indicator of successful durable isolation of the PVs. The findings suggest that confirmation of exit block may be warranted to improve AF ablation outcomes., (©2013, The Authors. Journal compilation ©2013 Wiley Periodicals, Inc.)

Background: Earlier studies in patients with reduced left ventricular ejection fraction (LVEF) ≤35% and prolonged QRS showed better survival outcomes with cardiac resynchronization therapy (CRT). Some patients respond dramatically to CRT by improving their LVEF to the normal range and are considered "super-responders." Our aim was to determine whether super-responders survival increases to levels comparable to the general population. We compared the survival of super-responders to the general population matched for age and sex., Methods: Of 909 patients with CRT device implantation between September 1998 and July 2008, 814 patients had pre- and post-CRT echocardiogram. A total of 95 patients with LVEF ≥ 50% following CRT were classified as super-responders. For 92 super-responders, who had U.S. Social Security numbers, an age- and sex-matched example was selected from the Social Security Life Tables. An expected survival plot of the matched population was then compared to the actual survival of super-responders., Results: Super-responders had comparable survival to the age-sex matched general population (P = 0.53), and Kaplan-Meier survival analysis in 92 patients showed that super-responders with CRT pacemakers had similar survival to those with CRT implantable cardioverter defibrillators (P = 0.77). Super-responders were more likely to be females (54% vs 25%, P < 0.001) and less likely to have significant coronary artery disease (62% vs 42%, P < 0.001)., Conclusions: Normalization of LVEF by CRT improves survival to levels comparable to the general population. This observation favors the concept that some CRT candidates have a cardiomyopathy likely generated by the conduction abnormality that is reversible through biventricular pacing., (©2013, The Authors. Journal compilation ©2013 Wiley Periodicals, Inc.)

Background: The relationship between QRS narrowing and response to cardiac resynchronization therapy (CRT) has been controversial., Objective: We sought to analyze the relationship between QRS narrowing and reverse remodeling in patients undergoing CRT, taking into account potential confounders including pre-CRT QRS duration and underlying QRS morphology., Methods: We reviewed pre- and postimplant electrocardiograms and echocardiograms in a cohort of 233 patients undergoing the new implantation of a CRT device between December 2001 and September 2006. For inclusion in the final cohort, patients had New York Heart Association classes II-IV heart failure, left ventricular ejection fraction (LVEF) ≤ 40%, and QRS duration ≥120 ms. Response to CRT was defined as a reduction in left ventricular end-systolic volume (LVESV) of ≥10%. A multivariate model was constructed to determine the relationship between QRS change and response to CRT., Results: Patients with QRS narrowing had significantly greater reductions in left ventricular end-diastolic volume (LVEDV) (mL) (-26.5 ± 52.5 vs -4.8 ± 44.0, P = 0.002) and LVESV (mL) (-34.0 ± 55.5 vs -9.9 ± 45.8, P = 0.002) and improvement in LVEF (%) (8.9 ± 12.8 vs 4.5 ± 9.0, P = 0.007) than patients without narrowing. In univariate analysis, female gender (P = 0.0002), percent QRS narrowing from baseline (P = 0.008), lack of nitrate (P≤0.0001) and antiarrhythmic medication use (P = 0.01), lack of a nonspecific intraventricular conduction delay (=0.02), nonischemic cardiomyopathy (P = 0.003), and lower pre-CRT LVEDV (P = 0.006) and LVESV [P = 0.01]) were associated with responders. In a multivariate model, QRS narrowing, indexed to the baseline QRS duration, remained strongly associated with response (odds ratio 0.08 [0.01-0.56], P = 0.01)., Conclusions: After adjusting for potential confounders, QRS narrowing, indexed to baseline QRS duration, is associated with enhanced reverse ventricular remodeling following CRT., (©2011, The Authors. Journal compilation ©2011 Wiley Periodicals, Inc.)

Background: Rapid, disorganized firing from a pulmonary vein (PV) focus may initiate atrial fibrillation. The natural history of PV atrial tachycardia (AT), resulting in a slower, more organized form of firing, is less clear. Furthermore, the optimal therapeutic approach to a PV AT is poorly defined., Objective: This study assessed the characteristics and long-term outcomes of focal ablation versus PV isolation for ATs arising from a single PV., Methods: We reviewed 886 consecutive patients who underwent an AT radiofrequency ablation at our institution from January 1997 through August 2008., Results: Twenty-six patients had focal AT with a mean cycle length of 364 +/- 90 ms that arose from within a single PV. Ten patients underwent focal ablation of their AT and 16 patients underwent PV isolation of the culprit vein. All procedures were acutely successful. The average follow-up was 25 months (range 2-90 months). There were three recurrences of AT in patients who underwent a focal ablation. There were no recurrences in patients who underwent targeted PV isolation (P = 0.046). No patients developed atrial fibrillation or AT from another focus during the follow-up period., Conclusion: PV AT can be successfully treated with single vein isolation or focal ablation with a low risk of recurrence or the development of atrial fibrillation. PV isolation may be the preferred approach when the AT focus arises from a site distal to the ostium where targeted ablation could result in phrenic nerve injury or occlusion of a pulmonary venous branch.

Objective: To identify subgroups of heart failure patients who might benefit from biventricular pacing., Background: Cardiac resynchronization therapy (CRT) improves the quality of life, New York Heart Association (NYHA) functional class, and exercise capacity and decreases hospitalizations for heart failure for patients who have severe heart failure and a wide QRS. It is unclear if other populations of heart failure patients would benefit from CRT., Methods: One hundred forty-four consecutive heart failure patients who underwent CRT and completed 3 months of follow-up were reviewed. Demographic, echocardiographic, electrocardiographic, and clinical outcome data were analyzed to assess the relationship of functional class and QRS duration before device implantation to postimplant outcomes., Results: There were 20, 88, and 36 patients in NYHA functional class II, III, and IV, respectively. Thirty-four patients had right ventricular pacing and another 29 patients had a QRS duration < or = 150 ms. Patients who were in NYHA functional class II at baseline had significant improvement in left ventricular ejection fraction and indices of left ventricular remodeling after CRT. Similar significant findings were seen in the subgroup with right ventricular pacing at baseline after CRT. However, in the subgroup with a narrow QRS duration, there were no significant changes in the indices of left ventricular remodeling or in the NYHA functional class and there was a significant increase in the QRS duration. For the study cohort as a whole, an improvement in NYHA functional class after CRT correlated with a significant decrease in adverse clinical outcomes., Conclusions: Heart failure patients who were in NYHA functional class II and those with right ventricular pacing appeared to benefit from CRT.

Background: The isolation of a pathogen is vital in the diagnosis and treatment of a device infection. A swab culture, despite poor sensitivity, is the most common method used in specimen collection., Objective: To determine the relative value of swab and tissue specimen cultures in patients with implantable cardiac pacemakers and defibrillators., Design: Prospective patient cohort study., Setting: A 1,000-bed tertiary referral center in Cleveland, Ohio., Patients: Consecutive patients with implantable cardiac pacemaker or defibrillator presenting for lead extraction from October 1, 2000 to March 31, 2001., Methods: Tissue and swab cultures were prospectively collected during pacemaker and implantable defibrillator surgeries that required lead extraction. Clinical manifestations, microbiology, and echocardiographic data were recorded in patients with and without a clinical diagnosis of device system infection., Results: Seventy-one patients with implantable pacemaker (n = 49, 69%), implantable defibrillator (n = 18, 25%), or both devices (n = 4, 6%) requiring lead extraction had pocket swab and tissue cultures for analysis. Infection was evident clinically in 35 (49%) of the patients and absent in the remainder. The most common bacteria isolated were coagulase-negative Staphylococcus (37%) and Staphylococcus aureus (10%). Patients with clinical infection had positive cultures more frequently (P = 0.002) by pocket tissue culture (n = 24, 69%) than by swab culture (n = 11, 31%). However, patients without clinical infections had positive cultures at similar rates by pocket tissue culture (n = 10, 28%) and by swab culture (n = 8, 22%; P = 0.48). Patients without clinical infection were not treated with other than perioperative antibiotics, and did not develop clinical infections., Conclusion: Pocket tissue cultures are more effective than pocket swab cultures for the isolation and identification of the infectious pathogens in cardiac device infections. Positive cultures by pocket swab or tissue cultures in the absence of clinical signs and symptoms of infection does not imply infection or the need for specific therapy.

Background: Infection is a devastating complication of permanent pacemakers (PMs) implantable cardioverter defibrillators (ICDs). Many implanting physicians commonly use povidone-iodine solution to irrigate the device pocket before implanting the device. We sought to assess if such a measure would alter the rate of infection., Methods: A total of 2,564 consecutive patients who received implantable PM or ICD devices between 1994 and 2002 were studied. Povidone-iodine was used for pocket irrigation in 53% and saline in 47%. A total of 18 (0.7%) patients developed pocket infections with 0.7% (10/1,359) in povidone-iodine (group I) and 0.6% (8/1,205) in saline (group II) pocket irrigation (p = ns). Groups I and II were studied for various clinical and demographic variables described in the results section., Results: There was no statistical difference in the baseline demographic and clinical characteristics between groups I and II, respectively. ICDs were most frequently infected than PMs (56% vs 44%). Most (83%) of the devices were dual chamber. Reopening of the pocket for either lead or generator replacement had a higher incidence of infection than new implants (61% vs 39%). There was no difference in the use of preimplantation antibiotic prophylaxis. Late (61%) and deep pocket infections (78%) were more common than early (39%) and superficial infections (22%). Blood cultures were positive in 67% and Staphylococcus aureus was the common most pathogen (50%). The mean duration of antibiotics use after the diagnosis of device infection was 35 +/- 23 days with 72% requiring device explantation. The device was reimplanted on the contralateral side in 56% cases. One patient in each group died due to device infection and related complications. No significant allergy to iodine was seen in either group., Conclusion: Povidone-iodine irrigation of the subcutaneous pocket did not alter the rates of pocket infection after pacemaker/defibrillator implantation.

The automatic ICD improves survival in patients with a history of sudden cardiac arrest. However, some patients do not meet the guidelines for ICD implantation or are unable to receive an implantable device. This study tested the hypothesis that these patients could benefit from a wearable cardioverter defibrillator. Patients with symptomatic heart failure and an ejection fraction of <0.30 (WEARIT Study) or patients having complications associated with high risk for sudden death after a myocardial infarction or bypass surgery not receiving an ICD for up to 4 months (BIROAD Study) were enrolled into two studies. After a total of 289 patients had been enrolled in the trial (177 in WEARIT and 112 in BIROAD), prespecified safety and effectiveness guidelines had been met. Six (75%) of eight defibrillation attempts were successful. Six inappropriate shock episodes occurred during 901 months of patient use (0.67% unnecessary shocks per month of use). Twelve deaths occurred during the study 6 sudden deaths: 5 not wearing and 1 incorrectly wearing the device). Most patients tolerated the device although 68 patients quit due to comfort issues or adverse reactions. The results of the present study suggest that a wearable defibrillator is beneficial in detecting and effectively treating ventricular tachyarrhythmias in patients at high risk for sudden death who are not clear candidates for an ICD and may be useful as a bridge to transplantation or ICD in some patients.

Objectives: We report the acute success and long-term follow-up in consecutive patients undergoing catheter ablation of typical right atrial flutter (AFL) using different ablation technologies., Methods: One hundred and two patients presenting for treatment of AFL to our laboratory were included in the study. Based on availability and physician preference, ablation was performed with either a cooled-tip catheter (39 patients, group I), an 8- or 10-mm tip catheter connected to a high-power radiofrequency (RF) generator (25 patients, group II), or a 4- or 5-mm tip catheter (38 patients, group III). Acute ablation success was achieved in all group II and group III patients. Among the 38 patients undergoing ablation with the conventional catheter tip (group I), crossover to an 8-mm tip or a cooled tip ablation catheter was required in 11 patients (29%). The mean fluoroscopy time was significantly higher in group I (54.3 +/- 26.4 minutes) when compared to group II (39.6 +/- 19.6 minutes; P < 0.05) and group III (40 +/- 16 minutes; P = 0.0.5). After a mean follow up of 20 +/- 5 months no patient in group II experienced recurrence of AFL, whereas 18.4% (7 of 38 patients; P < 0.05) in group I and 10% (4 of 39 patients; P < 0.05) in group III had recurrence of AFL. Ablation technologies designed to obtain larger size lesions appeared to be more effective in achieving acute ablation success of AFL and in limiting the long-term recurrence rate of this arrhythmia.

Biventricular ICDs may offer increased benefit for patients with severe congestive heart failure and ventricular arrhythmia. Currently there are no approved dedicated biventricular ICDs available. Twenty-one consecutive patients who had approved nondedicated hardware implanted for biventricular pacing and defibrillation were included in this study. All device therapies were evaluated using stored electrograms. During mean follow-up at 13 +/- 7 months, 8 (36%) patients had inappropriate shocks. Ventricular fibrillation therapy was delivered for slow ventricular tachycardia because of double counting in two patients. In one patient, AV nodal reentrant tachycardia below detection rate cut off triggered device therapy because of ventricular double counting. Sinus tachycardia or premature atrial contraction initiating AV conduction and ventricular double counting resulted in shocks in five patients. The number of shocks per patient ranged from 1 to 64. Two patients required transient disconnection of the LV lead and subsequent ICD generator replacement for premature battery depletion. Two patients required AV junction ablation and three needed slow pathway ablation. Two patients were treated by upgrading to a device that was capable of a higher atrial tracking rate. The patients with impaired AV conduction or constant ventricular pacing did not have inappropriate therapy for sinus tachycardia or supraventricular arrhythmia. Use of conventional nondedicated hardware for biventricular pacer/defibrillator is feasible but should be considered only in patients with poor AV node function or less likely to require antitachycardic therapy, to avoid ICD double counting of ventricular sensed events and consequent high incidence of inappropriate therapies.

The purpose of this study was to assess the feasibility and long-term results of empirical isolation of both superior pulmonary veins in patients with chronic AF. Although localizing and ablating the focal triggers of AF has been proven an effective approach, this strategy is time consuming, often requires multiple procedures, and carries the risk of pulmonary vein stenosis. Whether ostial electrical isolation of the superior pulmonary veins, without initial detailed mapping, is a more efficient approach is not known. The study included 71 consecutive patients who had chronic AF. Using a nonfluoroscopic electroanatomic mapping system, the left and right superior pulmonary veins were ablated circumferentially at the venoatrial junction, with the aim of achieving electrical isolation of the veins. Following ablation, if frequent atrial ectopies were present, mapping and ablation were considered. The patients were periodically followed with 48-hour Holter and loop recorder monitoring. After the ablation of the right and left superior pulmonary veins 59 (83%) of 71 patients maintained sinus rhythm without premature atrial beats. The remaining 12 patients underwent further mapping and ablation including 5 patients who required isolation of the left inferior pulmonary veins. True electrical isolation could be achieved only in 45 (31%) of the 147 targeted veins. At the latest follow-up (mean 29 +/- 8 months), 80% of the patients with upper vein isolation remained in sinus rhythm off medications, 62% of the patients maintained sinus rhythm on previously ineffective medications, and 17% continued to be in AF. Fourteen (20%) patients developed intermittent episodes of left atrial flutter, and mapping in these patients revealed large electrically silent areas in the left atrium. Empirical isolation of pulmonary veins appeared to be an effective approach to help maintain sinus rhythm in patients with chronic AF. True electrical isolation of the pulmonary veins was associated with a higher likelihood of long-term success. Left atrial flutter was seen in a significant number of patients at long-term follow-up.

Atrial premature depolarizations (APDs) originating from focal sites, particularly the pulmonary veins (PV), may become triggers of atrial fibrillation (AF). Accurate mapping of APDs with conventional methods may be time consuming and expose the patient to unnecessary instrumentation of the left atrium. We hypothesized that the atrial activation sequence recorded using a simple system that includes an esophageal catheter and a custom-made 16-electrode catheter with two sets of floating electrodes eight in the coronary sinus and eight in the high right atrium) could be sufficient to localize the APDs. The study included 29 patients with frequent APDs and AF refractory to antiarrhythmic medications. The APD site of origin was confirmed with single-point sequential mapping techniques using the CARTO system ten patients) or by placement of multielectrode catheters in the right and left PV (19 patients). Of the 29 patients, 20 patients had a single APD focus; 8 patients had two different APD morphologies; and 1 patient had three APD foci. Mapping for ablation of the APD foci showed earliest activation in the left superior PV in 12 patients, right superior PV in 15 patients, right middle PV in 4 patients, right inferior PV in 1 patient, the lingular branch of the left superior PV in 2 patients, left inferior PV in 2 patients, and right atrium along the crista terminalis in 3 patients. The activation sequence and relative timing of the recordings obtained with our catheter configuration was highly predictive of right and left atrial origin and, more importantly, of right and left PV foci.

Nonthoracotomy leads (NTLs) with an iridium oxide (IROX) coating exhibit lower defibrillation thresholds (DFTs) than uncoated NTLs. We tested whether adding an IROX coating to an active pectoral can would influence defibrillation efficacy. However, the primary purpose of this study was to examine the impedance changes that occur at different voltages for uncoated titanium NTLs and identical NTLs with an IROX coating. We studied anesthetized pigs with an NTL placed in the right ventricle and coupled this to an active pectoral can. Biphasic waveform DFTs were obtained for the four NTLs and can combinations: uncoated NTL and uncoated can, uncoated NTL and IROX can, IROX NTL and uncoated can, and IROX NTL and IROX can. The respective energy DFTs were: 23.6 +/- 6.9, 24.1 +/- 6.7, 21.3 +/- 6.0, and 21.4 +/- 7.0 J. The IROX NTL DFTs were significantly lower (P < 0.05) than the uncoated NTL DFTs (either can), confirming our previous study. We then used a low tilt monophasic waveform to assess impedance changes. The impedance rise for each NTL/can combination was measured at 50, 100, 300, and 700 V. Comparisons of impedance changes between voltage levels showed that the impedance rise was inversely related to voltage and was greatest with uncoated NTLs. The IROX coating of the NTL reduced the impedance rise at all shock voltages, but was particularly beneficial at the lower voltages. No advantage was seen when the pectoral can was coated with IROX regardless of which NTL was used. Our results suggest that low voltage applications, such as atrial defibrillation, would benefit most from the IROX-coated NTL, and further studies are warranted in this area.

Ventricular fibrillation (VF) duration may be a factor in determining the defibrillation energy for successful defibrillation. Exponential biphasic waveforms have been shown to defibrillate with less energy than do monophasic waveforms when used for external defibrillation. However, it is unknown whether this advantage persists with longer VF duration. We tested the hypothesis that exponential biphasic waveforms have lower defibrillation energy as compared to exponential monophasic waveforms even with longer VF duration up to 1 minute. In a swine model of external defibrillation (n = 12, 35 +/- 6 kg), we determined the stored energy at 50% defibrillation success (E50) after both 10 seconds and 1 minute of VF duration. A single exponential monophasic (M) and two exponential biphasic (B1 and B2) waveforms were tested with the following characteristics: M (60 microF, 70% tilt), B1 (60/60 microF, 70% tilt/3 ms pulse width), and B2 (60/20 microF, 70% tilt/3 ms pulse width) where the ratio of the phase 2 leading edge voltage to that of phase 1 was 0.5 for B1 and 1.0 for B2. E50 was measured by a Bayesian technique with a total often defibrillation shocks in each waveform and VF duration randomly. The E50 (J) for M, B1, and B2 were 131 +/- 41, 57 +/- 18,* and 60 +/- 26* with 10 seconds of VF duration, respectively, and 114 +/- 62, 77 +/- 45,* and 72 +/- 53* with 1 minute of VF duration, respectively (*P < 0.05 vs M). There was no significant difference in the E50 between 10 seconds and 1 minute of VF durations for each waveform. We conclude that (1) the E50 does not significantly increase with lengthening VF durations up to 1 minute regardless of the shock waveform, and (2) external exponential biphasic shocks are more effective than monophasic waveforms even with longer VF durations.

Antegrade activation of the His-Purkinje system (HPS) results in synchronized activation of the right ventricular (RV) and left ventricular (LV) endocardia forming normal, narrow QRS duration (QRSD). An alteration in septal activation and transseptal conduction time have been reported to be the causes for QRSD widening seen with bundle branch block. However, reduced synchronization of activation of RV and LV endocardia as another potential mechanism for QRSD widening has not been systematically studied. Fifteen consecutive patients underwent radiofrequency ablation (RFA) for treatment of supraventricular tachycardia. After RFA, mean QRSD in normal sinus rhythm was 86 +/- 8 ms with mean HV interval of 40 +/- 5 ms. Right atrial (RA), coronary sinus (CS), simultaneous (S) RA-CS, RV apex (RVA), LV apex (LVA), and SRVA-LVA pacing were performed. Mean QRSD with RA, CS, SRA-CS pacing was similar to normal sinus rhythm (87 +/- 7, 87 +/- 8 and 88 +/- 8 ms respectively). Mean QRSD was significantly longer with SRVA-LVA and either RVA or LVA pacing alone compared to normal sinus rhythm (106 +/- 8, 146 +/- 12 and 157 +/- 13 ms, respectively). However, QRSD was significantly shorter with SRVA-LVA pacing compared to either RVA or LVA pacing alone (P < 0.0001). We conclude that shorter QRSD with SRVA-LVA pacing compared to either RVA or LVA pacing alone is due to elimination of transseptal conduction delay; longer QRSD with SRVA-LVA pacing compared to sinus or atrial paced rhythm is due to reduced synchronization of endocardial activation secondary to ectopic entry of impulses into the HPS network and inability to take advantage of the branching structure of the HPS. Therefore, in addition to transseptal conduction delay, reduced synchronization of endocardial activation is another potential mechanism for QRSD widening.

The impedance of defibrillation pathways is an important determinant of ventricular defibrillation efficacy. The hypothesis in this study was that the respiration phase (end-inspiration versus end-expiration) may alter impedance and/or defibrillation efficacy in a "hot can" electrode system. Defibrillation threshold (DFT) parameters were evaluated at end-expiration and at end-inspiration phases in random order by a biphasic waveform in ten anesthetized pigs (body weight: 19.1 +/- 2.4 kg; heart weight: 97 +/- 10 g). Pigs were intubated with a cuffed endotracheal tube and ventilated through a Drager SAV respirator with tidal volume of 400-500 mL. A transvenous defibrillation lead (6 cm long, 6.5 Fr) was inserted into the right ventricular apex. A titanium can electrode (92-cm2 surface area) was placed in the left pectoral area. The right ventricular lead was the anode for the first phase and the cathode for the second phase. The DFT was determined by a "down-up down-up" protocol. Statistical analysis was performed with a Wilcoxon matched pair test. The median impedance at DFT for expiration and inspiration phases were 37.8 +/- 3.1 omega, and 39.3 +/- 3.6 omega, respectively (P = 0.02). The stored energy at DFT for expiration and inspiration phases were 5.7 +/- 1.9 J and 6.0 +/- 1.0 J, respectively (P = 0.594). Shocks delivered at end-inspiration exhibited a statistically significant increase in electrode impedance in a " hot can" electrode system. The finding that DFT energy was not significantly different at both respiration phases indicates that respiration phase does not significantly affect defibrillation energy requirements.

Interrelations between QRS morphology, duration, and HV interval changes in a model of "complete" bundle branch block following right bundle branch radiofrequency ablation have not been subjected to systematic study. This article describes these interrelations in patients who underwent right bundle ablation. Over a period of 42 months, 16 patients underwent radiofrequency ablation of the right bundle for treatment of bundle branch reentrant tachycardia. All 16 patients had prolonged HV interval at baseline (minimum = 60 ms; mean = 68 +/- 8 ms). After ablation, one patient developed complete heart block; the remaining 15 patients developed complete right bundle branch block (RBBB) and further prolongation of the HV interval (increment = 24 +/- 16 ms). In 14 of these 15 patients, QRS duration was 138 +/- 26 ms before ablation and increased to 168 +/- 13 ms after ablation. In the remaining patient, the QRS duration was 160 ms before ablation and shortened to 144 ms following ablation despite further HV prolongation. Larger increases of HV interval after ablation were associated with smaller or negative changes in QRS duration (r = -0.77). Three was a direct relationship between QRS duration at baseline and the increment in HV interval after ablation (r = 0.70), and an inverse relationship between QRS duration before and after ablation (r = 0.84). Radiofrequency ablation of right bundle may be associated with an increase in HV interval and QRS duration. However, HV interval prolongation is not necessarily associated with QRS duration widening. A large change in HV interval is more likely to be associated with an already prolonged QRS duration before ablation and a lesser increase or even decrease in QRS duration after ablation. A shorter QRS duration before ablation is associated with a smaller HV interval increase following ablation but a greater increment in QRS duration. These findings are consistent with the concept that narrowness of QRS duration is due to synchronized activation of ventricular endocardium; whereas, QRS duration widening seen with His-Purkinje damage is due to reduced synchronization of endocardial activation.

The polarity of a monophasic and biphasic shocks have been reported to influence DFTs in some studies. The purpose of this study was to evaluate the effect of the first phase polarity on the DFT of a biphasic shock utilizing a nonthoracotomy "hot can" electrode configuration which had a 90-microF capacitance. We tested the hypothesis that anodal first phase was more effective than cathodal ones for defibrillation using biphasic shocks in ten anesthetized pigs weighing 38.9 +/- 3.9 kg. The lead system consisted of a right ventricular catheter electrode with a surface area of 2.7 cm2 and a left pectoral "hot can" electrode with 92.9 cm2 surface area. DFT was determined using a repeated "down-up" technique. A shock was tested 10 seconds after initiation of ventricular fibrillation. The mean delivered energy at DFT was 11.2 +/- 1.7 J when using the right ventricular apex electrode as the cathode and 11.3 +/- 1.2 J (P = NS) when using it as the anode. The peak voltage at DFT was also not significantly different (529.0 +/- 41.3 and 531.8 +/- 28.6 V, respectively). We concluded that the first phase polarity of a biphasic shock used with a nonthroracotomy "hot can" electrode configuration did not affect DFT.

The Endotak lead system and ICD has been used to treat patients with malignant ventricular arrhythmias. We analyzed the clinical characteristics of 1,053 patients who underwent implantation of the Endotak lead system with or without a subcutaneous patch. Group A consisted of 567 patients receiving the Endotak lead with a subcutaneous patch; group B consisted of 486 patients receiving the Endotak lead alone. The 2-year survivals from sudden death, cardiac death, and total death in groups A and B were 97.6%/98.2% (P = 0.38), 88.6%/92.7% (P = 0.09), and 84.7%/86.8% (P = 0.06), respectively. Minimum tested effective defibrillation energy at implantation was 17.2 +/- 5.2 J for group A and 15.8 +/- 5.1 J for group B (P < 0.01). The operative mortality was 1.8% in group A and 0.6% in group B (P = 0.09). The incidence of lead dislodgment, malfunction, and infection was 6.7% for group A and 3.5% for group B (P < 0.01). Sudden death survival was excellent in both groups with less lead complications in group B. The Endotak lead alone may be the preferred choice of lead configuration in those patients who have adequate defibrillation thresholds at implant.

The study assessed the long-term outcome of patients undergoing radiofrequency ablation of the right bundle for bundle branch reentrant ventricular tachycardia. Bundle branch reentrant tachycardia was diagnosed in 16 patients (ejection fraction 31% +/- 15%) who underwent electrophysiology study in our laboratory. All patients had His-Purkinje system conduction delay with mean HV interval of 68 +/- 8 ms. After ablation, right bundle branch block developed in 15 patients. One patient developed complete heart block, which was anticipated. One patient died of heart failure 9 months after ablation. Two patients were successfully bridged to heart transplantation 0.5 and 13 months, respectively, after ablation. Two patients received implantable defibrillators for other ventricular tachycardias. One patient had syncope 11 months after ablation, but there was no evidence of ventricular tachycardia or heart block in repeat electrophysiology study. This patient died suddenly 29 months after ablation. The remaining nine patients were alive and well for a mean follow-up of 19 +/- 10 months. Radiofrequency ablation of the right bundle branch is an effective therapy for treatment of bundle branch reentrant ventricular tachycardia. Survival is excellent provided that other types of ventricular tachycardia, when present, are treated as well. This technique may be helpful in management of patients who have unacceptable frequent shocks from their implanted defibrillators and may be helpful in avoiding implantation of such a device completely in others. In some patients with terminal heart failure and incessant ventricular tachycardia, this procedure can function as a bridge to cardiac transplantation.

Among the various therapy options for survivors of ventricular tachycardia-ventricular fibrillation (VT-VF), the implantable cardioverter defibrillator (ICD) seems most promising. It reliably terminates VT-VF and thus significantly impacts sudden cardiac death (SCD) survival. It is more effective than any of the known antiarrhythmic drugs in prevention of SCD, particularly among survivors of cardiac arrest. Compared to VT surgery, the ICD therapy can be offered to a larger pool of patients and can be placed at a lower surgical risk. With proper patient selection, ICD therapy is of major benefits to its recipients since it markedly reduces the chances of VT-VF related mortality; the main cause of premature death in this population. The ICD therapy is cost effective when compared to other medical interventions and could be more so if the implant is carried out early in the course of VT-VF management.

The implantable cardioverter defibrillator has become an important therapeutic modality for treatment of life-threatening ventricular tachyarrhythmias. Recent reports have suggested that patients who receive appropriate shocks from this device have an inordinately high overall mortality, and questioned the extent of benefit these patients derive from the implant. This report analyzed the survival among 184 patients who received the implantable cardioverter defibrillator to assess survival differences between patients who received appropriate shocks versus those who did not. At a mean follow-up of 24 +/- 18.7 months, 68 patients received an appropriate shock from their device while 116 did not receive an appropriate shock. Overall survival of the entire population was quite similar to those published by others. There was no significant difference between overall survival of patients who received an appropriate shock versus those who did not. However, there was a statistically significant difference in sudden death mortality. The group of patients that received appropriate shocks included all five sudden deaths. This observation suggested that sudden death in this population was likely due to ventricular tachyarrhythmias rather than strictly bradycardia or asystole. The "benefit" of the device to the entire population was also assessed by estimating survival after receipt of the first appropriate shock. Using this approach, an estimated 10% of patients died without receiving an appropriate shock. In other words, ultimately, 90% of patients were expected to benefit from the device. This survival curve, which initiated only after receipt of the first appropriate shock was fairly similar to those estimated from conventional methods. Therefore, survival after receipt of an appropriate shock was comparable to overall survival and there was no significant difference between survival of patients who received appropriate shocks and those who did not.

In most reports on patients receiving implantable cardioverter defibrillators, shocks were received mainly during the first 2 to 3 years. Thus, the question had been raised as to the need for device replacement after 3 or 4 years if no shocks had been received. In order to answer this question, shock experience in 184 patients receiving the implantable cardioverter defibrillator was analyzed. Patients were followed for a mean of 24 +/- 18.7 months. A patient's shock was judged to be appropriate if there was electrocardiographic documentation of sustained ventricular tachyarrhythmia at the time of shock or if it was preceded by sudden onset of presyncopal or syncopal symptoms. The majority of patients had coronary artery disease. In approximately two-thirds of patients, left ventricular ejection fraction was below 40%. One hundred fourteen patients had inducible sustained monomorphic ventricular tachycardia. On follow-up, there were 29 deaths, five of which were sudden. Sixty-eight patients received an appropriate shock during follow-up (37%). Over 90% of these 68 received their first shock within the 2 years after implant. The actuarial risk of receiving an appropriate shock by the fifth year after implant was 69%. Conversely, 31% of patients who survived 5 years had not received an appropriate shock. Hazard analysis indicates that there is a high incidence of first appropriate shock during the year following implant. Subsequently, the incidence dropped to a relatively steady rate with a rise in this rate during the fifth year. This analysis suggested a bimodal distribution of appropriate shocks.(ABSTRACT TRUNCATED AT 250 WORDS)

The usual mode of controlling ventricular rate after His-bundle ablation is placement of a ventricular demand rate responsive pacemaker. Atrioventricular synchrony is therefore lost in individuals whose atrial rhythm disturbances are paroxysmal. Thirty-seven His ablations were performed at this institution, since January of 1983, for atrial rhythm disturbances that were not suppressible with medical therapy alone. Of those, ten patients were identified whose atrial rhythm disturbances were intermittent and who would otherwise benefit by having proper atrioventricular sequence during sinus rhythm. These patients underwent placement of a dual chamber pacemaker system having a fallback mode. At a mean follow-up period of 17 +/- 11 months, eight patients continued to maintain proper atrioventricular sequence with ventricular pacing tracking atrial activation during sinus rhythm. Supraventricular tachyarrhythmic attacks were associated with attainment of the programmed upper rate limit at which time the fallback mode was activated and the pacemaker automatically converted to a ventricular demand (VVI) mode. Restoration of normal sinus rhythm was associated with restoration of proper atrioventricular sequence. Two patients have developed chronic atrial fibrillation and their pacemakers continue to function in the fallback mode as VVI devices. In conclusion, intermittent supraventricular tachyarrhythmias which are resistant to drug therapy can be treated with His ablation and dual chamber pacing utilizing special pacemaker features such as the fallback mode.

Mortality in patients with cardiovascular disease is generally due to pump failure or lethal ventricular arrhythmias. In patients with ventricular tachycardia (VT) or ventricular fibrillation (VF) and poor left ventricular (LV) function the death rate is particularly high. The overall incidence of premature arrhythmic death rate in patients with poor LV function is not totally clear. Since implantable cardioverter defibrillator (ICD) could prevent arrhythmic death in any population, we proceeded to analyze mortalities in patients with poor LV function who received ICD. Among a total of 200 consecutive patients receiving ICD at our institution, 68 (34%) had LV ejection fraction (LVEF) of less than 30%. Thirty-one of these (45%) experienced appropriate ICD discharges and 17/31 (55%) had multiple shocks. Survival curves in this population revealed a 5 year projected overall survival of 11% whereas an actual survival was 60%. Even those who ultimately died from nonsudden causes, life was prolonged by ICD in a significant number of cases. Based upon these findings it is concluded that ICD has a major impact on survival in patients with poor LV function suggesting that many of these patients die prematurely from arrhythmia causes.