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Introduction: Long QT syndrome (LQTS) was first described in the 1960s. It manifests clinically as syncope, cardiac arrest or sudden cardiac death. LQTS can be caused by 15 different genes. These mutations lead to action potential prolongation by causing impaired repolarizing currents. Case Discussion: A 29-year-old previously healthy Caucasian woman was admitted after recurrent episodes of syncope that happened within 1-month prior to the presentation. She was hemodynamically stable with normal vitals. Her ECG showed normal sinus rhythm with corrected QT (QTc) of 598ms. In the ED, she suffered an episode of sustained monomorphic ventricular tachycardia (VT) and underwent cardioversion. She was started on amiodarone infusion. Serial ECGs showed prolonged QTc. She had another episode of pulseless VT that terminated without defibrillation. She was transferred to our facility for further care. Her family history was significant for paternal aunt who had died unexpectedly at the age of 39. All her lab work including electrolytes, thyroid panel, cardiac enzymes, inflammatory markers and extended drug screen was unrevealing. Transthoracic echocardiogram showed normal biventricular size and function. Decision making: She was started on propranolol for possible LQTS. Cardiac MR did not show any evidence of structural abnormalities. Genetic panel was sent. Since myocarditis or familial LQTS could not be ruled out, we proceeded with implantable cardioverter defibrillator (ICD) implantation for secondary prevention. She was discharged home on nadolol. Conclusion: In the absence of genetic information, LQTS can be diagnosed in symptomatic patients with QTc >480msec on serial ECGs after excluding secondary causes. Schwartz score comprising of ECG findings, symptoms, clinical & family history is diagnostic when greater than 3.5. Beta-blockers are indicated in all patients with a clinical diagnosis. Patients must avoid any QT prolonging agents and strenuous exercise. An ICD is indicated in patients who suffered cardiac arrest. ICD may also be considered for primary prevention in high risk patients.

Background We describe a technique to localize the ablation target in patients with an unusual variant of slow/fast atrioventricular nodal reentrant tachycardia (AVNRT) using a slow pathway connecting to the basal inferolateral left atrium. Methods Consecutive patients with slow/fast AVNRT were included. During stable slow/fast AVNRT, a single late atrial extrastimulus (AES) was delivered at the inferolateral left atrium near the mitral annulus. Advancing the next His bundle potential by ≥5 ms, followed by resetting of the tachycardia cycle length, indicated that the AES engaged the anterograde slow pathway. The latest AES resetting AVNRT was considered to be in close proximity to the atrial end of the anterograde slow pathway and was selected as the ablation target. Results In 10 of 843 (1.2%) patients, ablation at the inferolateral left atrium was required. All patients had had failed ablation at the inferior triangle of Koch and roof of the coronary sinus. In all 10 patients, a late AES advanced the His bundle potential by ≥10 ms and reset the tachycardia. Ablation at that site eliminated slow pathway conduction and terminated the tachycardia. Ablation was successful at the site of the latest AES, delivered 49±12 ms after the onset of the His bundle potential. No recurrent tachycardia was noted at 1 year of follow-up. Conclusions The inferolateral left atrium slow pathway is used in a small subset of patients with slow/fast AVNRT. Accurate localization of the ablation target can be achieved by delivering late AES during AVNRT (resetting response).

Background Radiofrequency catheter ablation is used to treat recurrent ventricular tachycardia (VT). Objectives This study evaluated long-term safety and effectiveness of radiofrequency catheter ablation using an open-irrigated catheter. Methods Patients with sustained monomorphic ventricular tachycardia associated with coronary disease were analyzed for cardiovascular-specific adverse events within 7 days of treatment, hospitalization duration, 6-month sustained monomorphic ventricular tachycardia recurrence, quality of life measured by the Hospital Anxiety and Depression Scale, long-term (1-, 2-, and 3-year) survival, symptomatic VT control, and amiodarone use. Results Overall, 249 patients, mean age 67.4 years, were enrolled. The cardiovascular-specific adverse events rate was 3.9% (9 of 233) with no strokes. Noninducibility of targeted VT was achieved in 75.9% of patients. Post-ablation median hospitalization was 2 days. At 6 months, 62.0% (114 of 184) of patients had no sustained monomorphic ventricular tachycardia recurrence; the proportion of patients with implantable cardioverter-defibrillator shocks decreased from 81.2% to 26.8% (p Conclusions Radiofrequency catheter ablation reduced implantable cardioverter-defibrillator shocks and VT episodes and improved quality of life at 6 months. A steady 3-year nonrecurrence rate with reduced amiodarone use and hospitalizations indicate improved long-term outcomes. (NaviStar ThermoCool Catheter for Endocardial RF Ablation in Patients With Ventricular Tachycardia [THERMOCOOL VT]; NCT00412607 )

Microangiopathic hemolytic anemia (MAHA) is usually caused by infection, autoimmune disorders, and or genetic predisposition. More recently MAHA secondary to cocaine use has been described. We report a case of cocaine-induced MAHA presenting as non-ST elevation myocardial infarction (NSTEMI). A 44

Serum cardiac troponins I and T are reliable and highly specific markers of myocardial injury. Studies have shown that at least 20% of patients with severe aortic stenosis have detectable serum troponins. This case report describes a patient who presented as suspected acute coronary syndrome with markedly elevated troponin levels, who was later found to have normal coronaries and critical aortic stenosis. This case highlights the need for comprehensive and accurate physical examination in patients who present with angina. Critical aortic stenosis may cause such severe subendocardial ischemia as to cause marked elevation in cardiac markers and mimic an acute coronary syndrome. Careful physical examination will lead to an earlier use of non invasive techniques, such as echocardiography to confirm the correct diagnosis and the avoidance of inappropriate treatments such as intravenous nitroglycerin and glycoprotein IIb/IIIa inhibitors.

Background: A high-intensity-focused ultrasound balloon catheter (HIFU-BC) is designed to isolate pulmonary veins (PV) outside the ostia (PV antrum). This catheter uses a parabolic CO2 balloon (behind water balloon) to focus a 20-, 25-, or 30-mm diameter ring of ultrasound forward of the balloon (parallel to catheter shaft). The purpose of this study is to test the safety and efficacy of the HIFU-BC for PV antrum isolation in patients with atrial fibrillation (AF). Methods and Results: Twenty-seven patients with paroxysmal (19 patients) or persistent (8 patients) AF were studied. Double transseptal puncture was performed for left atrial deployment of a Lasso catheter (for PV mapping) and the 14 Fr HIFU-BC. The HIFU-BC was positioned outside the PV orifice over a guidewire. HIFU energy (acoustic power 45 watts) was applied for 40 seconds with a 20-mm sonicating ring and 40 or 60 seconds with a 25-mm or 30-mm sonicating ring. No other ablation system was utilized. PV antrum isolation was attempted using HIFU-BC in 78 of 104 PVs (25/27 RSPVs, all 23 LSPVs, all 23 LIPVs, all four left common trunks and 3/27 RIPVs). HIFU-BC successfully isolated 68 (87%) of the 78PV antra with 1–26 (median 3) HIFU applications. The complications include transient bleeding from a distal branch of the left superior PV resulting from guidewire manipulation in one patient and right phrenic nerve injury in another patient. No PV stenosis (>50% narrowing) and no LA-esophageal fistula occurred. At the 12-month follow-up, 16 (59%) of the 27 patients were free of symptomatic episodes of AF (only 3 of the 16 patients were receiving antiarrhythmic medications). Conclusions: Forward-focused HIFU applications isolated PVs outside the PV ostium with elimination of AF in 16 (59%) of the 27 patients at 12 months following the single ablation procedure.

Radiofrequency catheter ablation is used to treat recurrent ventricular tachycardia (VT).This study evaluated long-term safety and effectiveness of radiofrequency catheter ablation using an open-irrigated catheter.Patients with sustained monomorphic ventricular tachycardia associated with coronary disease were analyzed for cardiovascular-specific adverse events within 7 days of treatment, hospitalization duration, 6-month sustained monomorphic ventricular tachycardia recurrence, quality of life measured by the Hospital Anxiety and Depression Scale, long-term (1-, 2-, and 3-year) survival, symptomatic VT control, and amiodarone use.Overall, 249 patients, mean age 67.4 years, were enrolled. The cardiovascular-specific adverse events rate was 3.9% (9 of 233) with no strokes. Noninducibility of targeted VT was achieved in 75.9% of patients. Post-ablation median hospitalization was 2 days. At 6 months, 62.0% (114 of 184) of patients had no sustained monomorphic ventricular tachycardia recurrence; the proportion of patients with implantable cardioverter-defibrillator shocks decreased from 81.2% to 26.8% (p 0.0001); the frequency of VT in implantable cardioverter-defibrillator patients with recurrences was reduced by ≥50% in 63.8% of patients; and the proportion with normal Hospital Anxiety and Depression Scale scores increased from 48.8% to 69.1% (p 0.001). Patient-reported VT remained steady for 1, 2, and 3 years at 22.7%, 29.8%, and 24.1%, respectively. Amiodarone use and hospitalization decreased from 55% and 77.2% pre-ablation to 23.3% and 30.7%, 18.5% and 36.7%, 17.7% and 31.3% at 1, 2, and 3 years, respectively.Radiofrequency catheter ablation reduced implantable cardioverter-defibrillator shocks and VT episodes and improved quality of life at 6 months. A steady 3-year nonrecurrence rate with reduced amiodarone use and hospitalizations indicate improved long-term outcomes. (NaviStar ThermoCool Catheter for Endocardial RF Ablation in Patients With Ventricular Tachycardia [THERMOCOOL VT]; NCT00412607).

Background Atrial fibrillation (AF) may occur without symptoms. Little is known about demographic features and prognostic information in patients with asymptomatic AF. Methods In the AFFIRM study, 4060 patients were randomized to either rhythm or rate control. At baseline, patients were identified as asymptomatic if they answered "no" to a 15-item questionnaire related to cardiac symptoms during AF in the 6 months before study entry. Results There were 481 (12%) asymptomatic patients at baseline. Compared with symptomatic patients, asymptomatic patients were more often men and had a lower incidence of coronary artery disease and congestive heart failure, but had more cerebrovascular events. Asymptomatic patients had a longer duration of AF, a lower maximum heart rate, and better left ventricular function. They received fewer cardiac medications and fewer therapies to maintain sinus rhythm. At 5 years, there was a trend for better survival in asymptomatic patients (81% vs 77%, P = .058), and they were more likely to be free from disabling stroke or anoxic encephalopathy, major bleeding, and cardiac arrest (79% vs 67%, P = .024). However, mortality and major events were similar after correction for baseline differences. Conclusions Patients with asymptomatic AF have less serious heart disease but more cerebrovascular disease. Asymptomatic patients receive different therapies than symptomatic patients. However, the absence of symptoms and the differences in treatment does not confer a more favorable prognosis when differences in baseline clinical parameters are considered. Anticoagulation should be considered in these patients.

Objectives We investigated whether inhibition of endogenous angiotensin II signaling reduces the recurrence rate of atrial fibrillation (AF) in patients enrolled in the Atrial Fibrillation Follow-up Investigation of Rhythm Management (AFFIRM) study. Background Structural and electrical remodeling contribute to AF. Previous experimental studies have implicated the angiotensin II signaling pathway in this process, and recent clinical evidence supports a beneficial effect of inhibiting angiotensin II activity. Methods Using the AFFIRM database, we retrospectively identified a cohort of patients randomized to the rhythm-control arm who were in sinus rhythm. Exposure to angiotensin II receptor blockers or angiotensin-converting enzyme inhibitors (ANGI) was determined, and the time to first recurrence of AF was compared between ANGI users and nonusers. Results The study cohort included 732 patients not taking ANGI through the initial 2-month follow-up and 421 patients taking ANGI during this time. Patients in the ANGI group more likely had hypertension, diabetes, coronary artery disease, and congestive heart failure compared to patients not taking ANGI. Risk of AF recurrence in the ANGI treatment group did not differ from the risk observed in patients not taking the drugs (hazard ratio [HR] = 0.91, 95% confidence interval [CI] = 0.77–1.09). However, in patients with congestive heart failure or impaired left ventricular function, ANGI use was associated with a lower risk of AF recurrence. Conclusions This analysis provides evidence that ANGI use may be beneficial in some patient subgroups with AF and underscores the need for randomized clinical trials defining more fully the role of angiotensin II inhibition in treating AF.

Introduction: The implantable cardioverter defibrillator (ICD) is commonly used to treat patients with documented sustained ventricular tachycardia (VT) or ventricular fibrillation (VF). Arrhythmia recurrence rates in these patients are high, but which patients will receive a therapy and the forms of arrhythmia recurrence (VT or VF) are poorly understood. Methods and Results: The therapy delivered by the ICD was examined in 449 patients randomized to ICD therapy in the Antiarrhythmics Versus Implantable Defibrillators (AVID) Trial. Events triggering ICD shocks or antitachycardia pacing (ATP) were reviewed for arrhythmia diagnosis, clinical symptoms, activity at the onset of the arrhythmia, and appropriateness and results of therapy. Both shock and ATP therapies were frequent by 2 years, with 68% of patients receiving some therapy or having an arrhythmic death. An appropriate shock was delivered in 53% of patients, and ATP was delivered in 68% of patients who had ATP activated. The first arrhythmia treated in follow-up was diagnosed as VT (63%), VF (13%), supraventricular tachycardia (18%), unknown arrhythmia (3%), or due to ICD malfunction or inappropriate sensing (3%). Acceleration of an arrhythmia by the ICD occurred in 8% of patients who received any therapy. No physical activity consistently preceded arrhythmias, nor did any single clinical factor predict the symptoms of the arrhythmia. Conclusion: Delivery of ICD therapy in AVID patients was common, primarily due to VT. Inappropriate ICD therapy occurred frequently. Use of ICD therapy as a surrogate endpoint for death in clinical trials should be avoided. (J Cardiovasc Electrophysiol, Vol. 14, pp. 940-948, September 2003)

Because many episodes of ventricular fibrillation (VF) are believed to be triggered by ventricular tachycardia (VT), patients who present with VT or VF are usually grouped together in discussions of natural history and treatment. However, there are significant differences in the clinical profiles of these 2 patient groups, and some studies have suggested differences in their response to therapy. We examined arrhythmias occurring spontaneously in 449 patients assigned to implantable cardioverter-defibrillator (ICD) therapy in the Antiarrhythmics Versus Implantable Defibrillators (AVID) trial to determine whether patients who receive an ICD after VT have arrhythmias during follow-up that are different from patients who present with VF. ICD printouts were analyzed both by a committee blinded to the patients' original presenting arrhythmia and by the local investigator. During 31 +/- 14 months of follow-up, 2,673 therapies were reported. Patients who were enrolled in the AVID trial after an episode of VT were more likely to have an episode of VT (73.5% vs 30.1%, p

Background— The coronary sinus (CS) has a myocardial coat (CSMC) with extensive connections to the left and right atria. We postulated that some posteroseptal and left posterior accessory pathways (CSAPs) result from connections between a cuff of CSMC extending along the middle cardiac vein (MCV) or posterior coronary vein (PCV) and the ventricle. The purpose of the present study was to use CS angiography and mapping to define and determine the incidence of CSAPs and determine the relationship to CS anatomy. Methods and Results— CSAP was defined by accessory pathway (AP) potential or earliest activation in the MCV or PCV and late activation at anular endocardial sites. A CSAP was identified in 171 of 480 patients undergoing ablation of a posteroseptal or left posterior AP. CS angiography revealed a CS diverticulum in 36 (21%) and fusiform or bulbous enlargement of the small cardiac vein, MCV, or CS in 15 (9%) patients. The remaining 120 (70%) patients had an angiographically normal CS. A CSMC extension potential (CSE), like an AP potential, was recorded in the MCV in 98 (82%), in the PCV in 13 (11%), in both the MCV and PCV in 6 (5%), and in the CS in 3 (2%) of 120 patients. CSMC potentials were recorded between the timing of atrial and CSE potentials. Conclusions— CSAPs result from a connection between a CSMC extension (along the MCV or PCV) and the ventricle. The CS is angiographically normal in most patients.

Troponin I Levels After Spontaneous ICD Shocks.Introduction: Serum cardiac troponin I (cTnI) is a sensitive and specific marker for myocardial injury. Myocardial ischemia and/or injury can be a trigger for ventricular arrhythmias. The aim of this study was to assess the frequency and significance of elevated serum cTnI levels after spontaneous implantable cardioverter defibrillator (ICD) shocks. Methods and Results: Serial cTnI measurements and ECGs were performed in 35 patients with transvenous ICDs who were admitted after spontaneous ICD shocks. Elevated cTnI levels were found in 18 patients (51%). Acute coronary syndrome was diagnosed in 5 (22%) of 23 patients with known coronary artery disease. After excluding the patients with acute coronary syndrome, elevated cTnI levels were present in 13 (43%) of 30 patients: 18% of patients with 3 shocks. Patients with elevated cTnI levels received a higher number of shocks (16 ± 18 vs 5 ± 7; P < 0.05) and had higher total delivered energies (475 ± 538 J vs 128 ± 184 J; P < 0.05) compared with patients with normal cTnI. Patients with acute coronary syndrome had higher peak cTnI levels (18 ± 16 ng/mL) compared with patients with elevated cTnI without acute coronary syndrome (3.8 ± 4.3 ng/mL; P < 0.01). Conclusion: Serum cTnI rises occur in the majority of patients after multiple (> 3) spontaneous ICD discharges but are due to acute coronary syndrome only 14% of the time (22% of the time in patients with known coronary artery disease).

Unexplained Syncope in AVID.Introduction: A prospective registry and substudy were conducted in the Antiarrhythmics Versus Implantable Defibrillators (AVID) Study to clarify the prognosis and recurrent event rate, risk factors, and impact of implantable cardioverter defibrillator (ICD) therapy in patients with unexplained syncope, structural heart disease, and inducible ventricular tachyarrhythmias. Methods and Results: Included in the AVID registry were patients from all participating sites who had “out of hospital syncope with structural heart disease and EP-inducible VT/VF with symptoms.” In addition, 13 collaborating sites provided more in-depth clinical and electrophysiologic data as part of a formal prospective substudy. Patients in the substudy were followed by local investigators for recurrent arrhythmic events and mortality. Registry patients were tracked for fatal outcomes by the National Death Index. A total of 429 patients with syncope were entered in the AVID registry, of whom 80 participated in the substudy. Of the substudy patients, 21 patients (26%) had inducible polymorphic ventricular tachycardia/ventricular fibrillation (VT/VF), 11 patients (14%) had sustained monomorphic VT < 200 beats/min, and 48 patients (60%) had sustained monomorphic VT ≥200 beats/min. The ICD was used as sole therapy in 75% of the syncope substudy patients (and with antiarrhythmic drug in an additional 9%) and in 59% of the syncope registry patients. Survival rates at 1 and 3 years were 93% and 74% for the substudy patients and 90% and 74% for the registry patients, respectively. Survival of the syncope substudy patients (predominantly treated by ICD) was similar to the VT patients treated by ICD and superior to the VT patients treated by an antiarrhythmic drug (P = 0.05) in the randomized main trial. Mortality events in the substudy were marginally predicted by ejection fraction (P = 0.06) but not by electrophysiologic study-induced arrhythmia. The significant predictor of increased mortality in the registry was age (P = 0.003) and of reduced mortality was treatment with ICD (P = 0.006). Conclusion: The results of these analyses support the role of the ICD as primary antiarrhythmic therapy in patients with unexplained syncope, structural heart disease, and inducible VT/VF at electrophysiologic study.

Background —Electrical storm, multiple temporally related episodes of ventricular tachycardia (VT) or ventricular fibrillation (VF), is a frequent problem among recipients of implantable cardioverter defibrillators (ICDs). However, insufficient data exist regarding its prognostic significance. Methods and Results —This analysis includes 457 patients who received an ICD in the Antiarrhythmics Versus Implantable Defibrillators (AVID) trial and who were followed for 31±13 months. Electrical storm was defined as ≥3 separate episodes of VT/VF within 24 hours. Characteristics and survival of patients surviving electrical storm (n=90), those with VT/VF unrelated to electrical storm (n=184), and the remaining patients (n=183) were compared. The 3 groups differed in terms of ejection fraction, index arrhythmia, revascularization status, and baseline medication use. Survival was evaluated using time-dependent Cox modeling. Electrical storm occurred 9.2±11.5 months after ICD implantation, and most episodes (86%) were due to VT. Electrical storm was a significant risk factor for subsequent death, independent of ejection fraction and other prognostic variables (relative risk [RR], 2.4; 95% confidence interval [CI], 1.3 to 4.2; P =0.003), but VT/VF unrelated to electrical storm was not (RR, 1.0; 95% CI, 0.6 to 1.7; P =0.9). The risk of death was greatest 3 months after electrical storm (RR, 5.4; 95% CI, 2.4 to 12.3; P =0.0001) and diminished beyond this time (RR, 1.9; 95% CI, 1.0 to 3.6; P =0.04). Conclusions —Electrical storm is an important, independent marker for subsequent death among ICD recipients, particularly in the first 3 months after its occurrence. However, the development of VT/VF unrelated to electrical storm does not seem to be associated with an increased risk of subsequent death.

Background The purpose of this study was to determine how often accessory atrioventricular (AV) pathways (AP) cross the AV groove obliquely. With an oblique course, the local ventriculoatrial (VA) interval at the site of earliest atrial activation (local-VA) and the local-AV interval at the site of earliest ventricular activation (local-AV) should vary by reversing the direction of the paced ventricular and atrial wavefronts, respectively. Methods and Results One hundred fourteen patients with a single AP were studied. Two ventricular and two atrial pacing sites on opposite sides of the AP were selected to reverse the direction of the ventricular and atrial wavefronts along the annulus. Reversing the ventricular wavefront increased local-VA by ≥15 ms in 91 of 106 (91%) patients. With the shorter local-VA, the ventricular potential overlapped the atrial potential along a 17.2±8.5-mm length of the annulus. No overlap occurred with the opposite wavefront. Reversing the atrial wavefront increased local-AV by ≥15 ms in 32 of 44 (73%) patients. With the shorter local-AV, the atrial potential overlapped the ventricular potential along an 11.9±8.9-mm length of the annulus. No overlap occurred with the opposite wavefront. Mapping during longer local-VA or local-AV identified an AP potential in 102 of 114 (89%) patients. Catheter ablation eliminated AP conduction in all 111 patients attempted (median, 1 radiofrequency application in 99 patients with an AP potential versus 4.5 applications without an AP potential). Conclusions Reversing the direction of the paced ventricular or atrial wavefront reveals an oblique course in most APs and facilitates localization of the AP potential for catheter ablation.

Background— Ablation of epicardial posteroseptal accessory pathways requires ablation within the coronary venous system. We assessed the risk of coronary artery (CA) injury with radiofrequency ablation (RFA) within the coronary venous system as a function of the distance between the CA and ablation site. We also examined the efficacy and safety of cryoablation close to a CA. Methods and Results— Two-hundred forty patients underwent ablation for epicardial posteroseptal accessory pathways. Coronary angiography was performed before ablation in the last 169 patients and was repeated after ablation if performed in the coronary venous system within 5 mm of a significant CA. The distance between the ideal ablation site and closest CA was 5 mm in 41 of 169 (25%) patients. CA injury was observed in 11 of 22 (50%) and 1 of 15 (7%) patients when RFA was performed within 2 and 3 to 5 mm of a CA, respectively. Cryoablation was performed in 26 patients with a significant CA located within 5 mm. Cryoablation alone eliminated epicardial posteroseptal accessory pathway conduction in 17 of 26 (65%) patients and in 8 patients with additional RFA without CA narrowing in any patient. During a follow-up period of 3 to 6 months, single procedure success rates were 90% and 77% for RFA and cryoablation at the ideal site, respectively. Conclusions— The risk of CA injury with RFA is correlated inversely with the distance from the ablation site. Cryoablation is a safe and reasonably effective alternative when a significant CA is located close to the ideal ablation site.

Background and hypothesis: The implantable cardioverter defibrillator (ICD) is the best available strategy to protect patients from life-threatening ventricular arrhythmia. Although unproven, it is commonly utilized to treat subjects with syncope, a negative clinical workup, structural heart disease, and inducible sustained monomorphic ventricular tachycardia (VT) on programmed electrophysiologic stimulation (EPS). The purpose of this paper was to validate this approach. Methods: We retrospectively identified 36 subjects who received primary ICD therapy for syncope in the setting of structural heart disease with inducible sustained monomorphic VT on EPS. The cohort was predominantly male (32/36) with underlying coronary artery disease (29/36). The mean left ventricular ejection fraction was 31 ± 12%, and a third of the patients (12/36) had undergone bypass surgery. Results: The study group was followed for a mean of 23 ± 15 months (range 3–81 months) and experienced an ICD event rate of 22% at 3 months, which increased to 55% at 36 months. This event rate was comparable with the 66% event rate seen in a group of patients with primary ICD therapy for spontaneous life-threatening VT treated during the same time period. No future predictors of ICD events in the study group could be identified. Conclusion: Syncope patients with negative workup, structural heart disease, and sustained monomorphic VT at EPS are at high risk for future tachyarrhythmic events. Based on present evidence, primary ICD therapy in this group appears warranted and justified.

ECG Localization of Accessory AV Pathways. Introduction: Delta wave morphology correlates with the site of ventricular insertion of accessory AV pathways. Because lesions due to radiofrequency (RF) current are small and well defined, it may allow precise localization of accessory pathways. The purpose of this study was to use RF catheter ablation to develop an ECG algorithm to predict accessory pathway location. Methods and Results: An algorithm was developed by correlating a resting 12-lead ECG with the successful RF ablation site in 135 consecutive patients with a single, anterogradely conducting accessory pathway (Retrospective phase). This algorithm was subsequently tested prospectively in 121 consecutive patients (Prospective phase). The ECG findings included the initial 20 msec of the delta wave in leads I, II, aVF, and V1 [classified as positive (+), negative (-), or isoelectric (±)] and the ratio of R and S wave amplitudes in leads III and V1 (classified as R ≥ S or R < S). When tested prospectively, the ECG algorithm accurately localized the accessory pathway to 1 of 10 sites around the tricuspid and mitral annuli or at subepicardial locations within the venous system of the heart. Overall sensitivity was 90% and specificity was 99%. The algorithm was particularly useful in correctly localizing anteroseptal (sensitivity 75%, specificity 99%), and mid-septal (sensitivity 100%, specificity 98%) accessory pathways as well as pathways requiring ablation from within ventricular venous branches or anomalies of the coronary sinus (sensitivity 100%, specificity 100%). Conclusion: A simple ECG algorithm identifies accessory pathway ablation site in Wolff-Parkinson-White syndrome. A truly negative delta wave in lead II predicts ablation within the coronary venous system.

Many antiarrhythmic agents have adverse hemodynamic effects which limit their use in patients with impaired ventricular function or during tachyarrhythmias. Ibutilide is an intravenous, selective class III antiarrhythmic agent that is effective for conversion of atrial fibrillation or flutter. This multicenter, randomized, placebo-controlled, dose-ranging study evaluated the effects of intravenous ibutilide on hemodynamic parameters during invasive monitoring in 47 patients with or without reduced left ventricular ejection fraction (LVEF) > 35% or < or = 35%. Patients received either placebo or ibutilide as a 10-minute loading and a 30-minute maintenance infusion using 1 of the following dosing regimens: placebo then placebo (n = 12); 0.01 then 0.002 mg/kg (n = 12); 0.02 then 0.004 mg/kg (n = 12); or 0.03 then 0.006 mg/kg (n = 11). Ibutilide significantly increased QT and QTc intervals in a dose-related manner with mean increases ranging from 51 to 99 ms, but did not alter the PR interval or QRS duration. During ibutilide infusion, a few small but statistically significant changes from baseline in several hemodynamic variables were present. However, the changes in cardiac output, pulmonary artery or capillary wedge pressures, blood pressure, or heart rate in patients receiving ibutilide were not significantly different from the changes in patients receiving placebo. Thus, ibutilide did not cause clinically important adverse hemodynamic effects, even in patients with depressed ventricular function. One patient developed 2 episodes of nonsustained torsades de pointes during ibutilide. These results demonstrate that with careful monitoring for proarrhythmia, ibutilide can be used safely from a hemodynamic standpoint in the acute treatment of arrhythmias, even in patients with reduced ventricular function.

Background Typical atrial flutter (AFL) results from right atrial reentry by propagation through an isthmus between the inferior vena cava (IVC) and tricuspid annulus (TA). We postulated that the eustachian valve and ridge (EVR) forms a line of conduction block between the IVC and coronary sinus (CS) ostium and forms a second isthmus (septal isthmus) between the TA and CS ostium. Methods and Results Endocardial mapping in 30 patients with AFL demonstrated atrial activation around the TA in the counterclockwise direction (left anterior oblique projection). Double atrial potentials were recorded along the EVR in all patients during AFL. Pacing either side of the EVR during sinus rhythm also produced double potentials, which indicated fixed anatomic block across EVR. Entrainment pacing at the septal isthmus and multiple sites around the TA produced a Δ return interval ≤8 ms in 14 of 15 patients tested. Catheter ablation eliminated AFL in all patients by ablation of the septal isthmus in 26 patients and the posterior isthmus in 4. AFL recurred in 2 of 12 patients (mean follow-up, 33.9±16.3 months) in whom ablation success was defined by the inability to reinduce AFL, compared with none of 18 patients (mean follow-up, 10.3±8.3 months) in whom success required formation of a complete line of conduction block between the TA and the EVR, identified by CS pacing that produced atrial activation around the TA only in the counterclockwise direction and by pacing the posterior TA with only clockwise atrial activation. Conclusions ( 1) The EVR forms a line of fixed conduction block between the IVC and the CS; (2) the EVR and the TA provide boundaries for the AFL reentrant circuit; and (3) verification of a complete line of block between the TA and the EVR is a more reliable criterion for long-term ablation success.

Background It is thought that only a thin layer of tissue adjacent to the electrode is heated directly by electrical current (resistive heating) during radiofrequency ablation. Most of the thermal injury is thought to result from conduction of heat from the surface layer. The purpose of this study was to determine whether lesion depth could be increased by producing direct resistive heating deeper in the tissue with higher radiofrequency power, allowed by cooling the ablation electrode with saline irrigation to prevent the rise in impedance that occurs when the electrode-tissue interface temperature reaches 100°C. Methods and Results In 11 anesthetized dogs, the thigh muscle was exposed and bathed with heparinized canine blood (36°C to 37°C). A 7F catheter, with a central lumen, a 5-mm tip electrode with six irrigation holes, and an internal thermistor, was positioned perpendicular to the thigh muscle and held at a constant contact weight of 10 g. Radiofrequency current was delivered to 145 sites (1) at high constant voltage (66 V) without irrigation (CV group, n=31), (2) at variable voltage (20 to 66 V) to maintain tip-electrode temperature at 80°C to 90°C without irrigation (temperature-control group, n=39), and (3) at high CV (66 V) with saline irrigation through the catheter lumen and ablation electrode at 20 mL/min (CV irrigation group, n=75). Radiofrequency current was applied for 60 seconds but was terminated immediately in the event of an impedance rise ≥10 Ω. Tip-electrode temperature and tissue temperature at depths of 3.5 and 7.0 mm were measured in all three groups (n=145). In 33 CV irrigation group applications, temperature was also measured with a separate probe at the center (n=18) or edge (n=15) of the electrode-tissue interface. In all 31 CV group applications, radiofrequency energy delivery was terminated prematurely (at 11.6±4.8 seconds) owing to an impedance rise associated with an electrode temperature of 98.8±2.1°C. All 39 temperature-control applications were delivered for 60 seconds without an impedance rise, but voltage had to be reduced to 38.4±6.1 V to avoid temperatures >90°C (mean tip-electrode temperature, 84.5±1.4°C). In CV irrigation applications, the tip-electrode temperature was not >48°C (mean, 38.4±5.1°C) and the electrode-tissue interface temperature was not >80°C (mean, 69.4±5.7°C). An abrupt impedance rise with an audible pop and without coagulum occurred in 6 of 75 CV irrigation group applications at 30 to 51 seconds, probably owing to release of steam from below the surface. In the CV and temperature-control group applications, the temperatures at depths of 3.5 (62.1±15.1°C and 67.9±7.5°C) and 7.0 mm (40.3±5.3°C and 48.3±4.8°C) were always lower than the electrode temperature. Conversely, in CV irrigation group applications, electrode and electrode-tissue interface temperatures were consistently exceeded by the tissue temperature at depths of 3.5 mm (94.7±9.1°C) and occasionally 7.0 mm (65.1±9.7°C). Lesion dimensions were smallest in CV group applications (depth, 4.7±0.6 mm; maximal diameter, 9.8±0.8 mm; volume, 135±33 mm 3 ), intermediate in temperature-control group applications (depth, 6.1±0.5 mm; maximal diameter, 11.3±0.9 mm; volume, 275±55 mm 3 ), and largest in CV irrigation group applications (depth, 9.9±1.1 mm; maximal diameter, 14.3±1.5 mm; volume, 700±217 mm 3 ; P Conclusions Saline irrigation maintains a low electrode-tissue interface temperature during radiofrequency application at high power, which prevents an impedance rise and produces deeper and larger lesions. A higher temperature in the tissue (3.5 mm deep) than at the electrode-tissue interface indicates that direct resistive heating occurred deeper in the tissue (rather than by conduction of heat from the surface).

The Brugada type pattern is characterized by a coved or saddleback shaped ST-segment elevation in the right precordial leads (V1-V3) on a surface 12 lead electrocardiogram (ECG). This pattern can be seen spontaneously, induced by sodium channel blocking drugs or rarely by hyperthermia. The mechanism is secondary to an alteration in the sodium channels induced by a febrile state. Such ECG's could easily be mistaken for acute ST segment elevation myocardial infarction and thus pose a unique clinical challenge to emergency room physicians. We report such a case of fever induced Brugada pattern and discuss the underlying mechanisms.

BACKGROUND Accessory pathways (APs) exhibiting "Mahaim fiber" physiology (antegrade conduction only, long conduction time, and decremental properties) often connect the lateral right atrium to the right bundle branch (right atriofascicular pathways). Potentials from these pathways have not been recorded previously. The purpose of this study was to determine whether AP activation potentials could be recorded from right atriofascicular APs and to determine whether these potentials could be used to localize a site for catheter ablation. METHODS AND RESULTS Of 26 consecutive patients referred for catheter ablation of an AP producing a preexcited (antidromic) atrioventricular (AV) reentrant tachycardia having a left bundle branch block pattern with short ventriculoatrial and long AV intervals, 23 (88.5%) were found to have a right atriofascicular AP. During antidromic AV reentrant tachycardia, (1) right atrial extrastimuli (that did not penetrant tachycardia, (1) right atrial extrastimuli (that did not penetrate the AV node) advanced the timing of the next QRS complex, indicating that the AP was connected to the right atrium; (2) earliest antegrade ventricular activation was recorded at the apical right ventricular free wall, and (3) ventricular activation was preceded by activation of the distal right bundle branch, indicating a fascicular insertion or a ventricular insertion close to the terminus of the right bundle branch. A single, discrete, high-frequency AP potential was recorded at the lateral, anterolateral, or posterolateral tricuspid annulus in 22 of the 23 patients 63 +/- 12 milliseconds after the local atrial potential and 83 +/- 23 milliseconds before the local ventricular potential during sinus rhythm. The AP potential was also recorded at sites along the right ventricular free wall between the tricuspid annulus and the site of earliest ventricular activation at the apical region. Programmed atrial stimulation and adenosine each produced prolongation of AP conduction time because of an increase in the A-AP interval and Wenckebach block proximal to the AP potential. Radiofrequency current applied at a site recording the AP potential (tricuspid annulus in 19 patients and right ventricular free wall in 3 patients) eliminated AP conduction in all 22 patients. Tachycardia has not recurred in any patient during 18 +/- 13 months of follow-up. AP conduction was absent in all 9 patients who had a follow-up electrophysiological study 3.8 +/- 1.7 months after ablation. CONCLUSIONS Right atriofascicular APs consist of two components. The proximal component is located at the lateral, anterolateral, or posterolateral tricuspid annulus, does not generate an AP potential recordable by catheter electrodes, and is responsible for the decremental conduction properties. The "distal" component extends from the tricuspid annulus to the distal right bundle branch at the apical right ventricular free wall and generates a large, high-frequency AP potential that accurately identifies a site for ablation.

Electrophysiologic studies have been used to elicit the mechanisms of the preexcitation syndromes and have become a therapeutic tool over the past decade. A thorough understanding of the physiology and anatomy of accessory pathways that are responsible for preexcitation and the associated arrhythmias is necessary before considering the various forms of intervention. The approach to patients with preexcitation syndromes is discussed, with an emphasis on the functional properties of accessory pathways and the associated arrhythmias.

Atrioventricular nodal reentrant tachycardia (AVNRT), the most common form of supraventricular tachycardia, results from conduction through a reentrant circuit comprising fast and slow atrioventricular nodal pathways. Antiarrhythmic-drug therapy is not consistently successful in controlling this rhythm disturbance. Catheter ablation of the fast pathway with radiofrequency current eliminates AVNRT, but it can produce heart block. We hypothesized that catheter ablation of the site of insertion of the slow pathway into the atrium would eliminate AVNRT while leaving normal (fast-pathway) atrioventricular nodal conduction intact.Eighty patients with symptomatic AVNRT were studied. Retrograde slow-pathway conduction (in which the earliest retrograde atrial potential was recorded at the posterior septum, close to the coronary sinus) was present in 33 patients. The retrograde atrial potential was preceded by a potential consistent with activation of the atrial end of the slow pathway (ASP). In 46 of the 47 patients without retrograde slow-pathway conduction, a potential with the same characteristics as the ASP potential was recorded during sinus rhythm. Radiofrequency current delivered through a catheter to the ASP site (in the posteroseptal right atrium or coronary sinus) abolished or modified slow-pathway conduction in 78 patients, eliminating AVNRT without affecting normal atrioventricular nodal conduction. In the single patient without ASP, the application of radiofrequency current to the proximal coronary sinus ablated the fast pathway and AVNRT: Atrioventricular block occurred in one patient (1.3 percent) with left bundle-branch block, after inadvertent ablation of the right bundle branch. AVNRT has not recurred in any patient during a mean (+/- SD) follow-up of 15.5 +/- 11.3 months. Electrophysiologic study 4.3 +/- 3.3 months after ablation in 32 patients demonstrated normal atrioventricular nodal conduction without AVNRT:Catheter ablation of the atrial end of the slow pathway using radiofrequency current, guided by ASP potentials, can eliminate AVNRT with very little risk of atrioventricular block.

Minimally invasive surgical (MIS) ablation, with pulmonary vein (PV) isolation and ganglionated plexi (GP) ablation, has proven highly successful for paroxysmal atrial fibrillation but has limited success in patients with persistent and long-standing persistent (P-LSP) AF. A set of linear left atrial (LA) lesions has been added to interrupt some macroreentrant components of P-LSP AF. This includes a Transverse Roof Line and Left Fibrous Trigone Line (from Roof Line to mitral annulus at the left fibrous trigone). With complete conduction block (CCB), these lesions should prevent single- or double-loop macroreentrant LA tachycardias from propagating around the PVs or mitral annulus. It is critical to identify whether CCB has been achieved and, if not, to locate the gap for further ablation, since residual gaps will support macroreentrant atrial tachycardias. Confirming CCB involves pacing close to one side of the ablation line and determining the direction of activation on the opposite side, by recording close bipolar electrograms at multiple paired sites (perpendicular and close to the ablation line) along the entire length of the line. Simpler approaches have been used, but all have limitations, especially when the conduction time across a gap is long. The extended lesion set was created after PV isolation and GP ablation in 14 patients with P-LSP AF. Mapping after the first set of radiofrequency applications for the Transverse Roof and Left Trigone Lines confirmed CCB in only 3/14 (21%) patients for each line, showing the importance of checking for CCB. During follow-up (median 8 months), 10/14 (71%) patients had no symptoms of atrial arrhythmia (7/10 off antiarrhythmic drugs). Of the remaining four patients, three have only infrequent episodes (self-terminating in 2/3). These preliminary results suggest that adding Roof and Trigone Lines may increase MIS success in patients with P-LSP AF. Accurate mapping techniques verify CCB and effectively locate gaps in ablation lines for further ablation.

The American College of Cardiology Foundation (ACCF), Society for Cardiovascular Angiography and Interventions, Society of Thoracic Surgeons, and the American Association for Thoracic Surgery, along with key specialty and subspecialty societies, conducted an appropriateness review of common clinical scenarios in which coronary revascularization is frequently considered. The clinical scenarios were developed to mimic common situations encountered in everyday practice and included information on symptom status, extent of medical therapy, risk level as assessed by noninvasive testing, and coronary anatomy. Approximately 180 clinical scenarios were developed by a writing committee and scored by a separate technical panel on a scale of 1 to 9. Scores of 7 to 9 indicate that revascularization was considered appropriate and likely to improve health outcomes or survival. Scores of 1 to 3 indicate revascularization was considered inappropriate and unlikely to improve health outcomes or survival. The mid range (4 to 6) indicates a clinical scenario for which the likelihood that coronary revascularization would improve health outcomes or survival was considered uncertain. For the majority of the clinical scenarios, the panel only considered the appropriateness of revascularization irrespective of whether this was accomplished by percutaneous coronary intervention (PCI) or coronary artery bypass graft surgery (CABG). In a select subgroup of clinical scenarios in which revascularization is generally considered appropriate, the appropriateness of PCI and CABG individually as the primary mode of revascularization was considered. In general, the use of coronary revascularization for patients with acute coronary syndromes and combinations of significant symptoms and/or ischemia was viewed favorably. In contrast, revascularization of asymptomatic patients or patients with low-risk findings on noninvasive testing and minimal medical therapy were viewed less favorably. It is anticipated that these results will have an impact on physician decision making and patient education regarding expected benefits from revascularization and will help guide future research.

The American College of Cardiology Foundation (ACCF), Society for Cardiovascular Angiography and Interventions, Society of Thoracic Surgeons, and the American Association for Thoracic Surgery, along with key specialty and subspecialty societies, conducted an appropriateness review of common clinical scenarios in which coronary revascularization is frequently considered. The clinical scenarios were developed to mimic common situations encountered in everyday practice and included information on symptom status, extent of medical therapy, risk level as assessed by noninvasive testing, and coronary anatomy. Approximately 180 clinical scenarios were developed by a writing committee and scored by a separate technical panel on a scale of 1 to 9. Scores of 7 to 9 indicate that revascularization was considered appropriate and likely to improve health outcomes or survival. Scores of 1 to 3 indicate revascularization was considered inappropriate and unlikely to improve health outcomes or survival. The mid range (4 to 6) indicates a clinical scenario for which the likelihood that coronary revascularization would improve health outcomes or survival was considered uncertain. For the majority of the clinical scenarios, the panel only considered the appropriateness of revascularization irrespective of whether this was accomplished by percutaneous coronary intervention (PCI) or coronary artery bypass graft surgery (CABG). In a select subgroup of clinical scenarios in which revascularization is generally considered appropriate, the appropriateness of PCI and CABG individually as the primary mode of revascularization was considered. In general, the use of coronary revascularization for patients with acute coronary syndromes and combinations of significant symptoms and/or ischemia was viewed favorably. In contrast, revascularization of asymptomatic patients or patients with low-risk findings on noninvasive testing and minimal medical therapy were viewed less favorably. It is anticipated that these results will have an impact on physician decision making and patient education regarding expected benefits from revascularization and will help guide future research.

Background Surgical or catheter ablation of accessory pathways by means of high-energy shocks serves as definitive therapy for patients with Wolff-Parkinson-White syndrome but has substantial associated morbidity and mortality. Radiofrequency current, an alternative energy source for ablation, produces smaller lesions without adverse effects remote from the site where current is delivered. We conducted this study to develop catheter techniques for delivering radiofrequency current to reduce morbidity and mortality associated with accessory-pathway ablation. Methods Radiofrequency current (mean power, 30.9 +/- 5.3 W) was applied through a catheter electrode positioned against the mitral or tricuspid annulus or a branch of the coronary sinus; when possible, delivery was guided by catheter recordings of accessory-pathway activation. Ablation was attempted in 166 patients with 177 accessory pathways (106 pathways in the left free wall, 13 in the anteroseptal region, 43 in the posteroseptal region, and 15 in the right free wall). Results Accessory-pathway conduction was eliminated in 164 of 166 patients (99 percent) by a median of three applications of radiofrequency current. During a mean follow-up (+/- SD) of 8.0 +/- 5.4 months, preexcitation or atrioventricular reentrant tachycardia returned in 15 patients (9 percent). All underwent a second, successful ablation. Electrophysiologic study 3.1 +/- 1.9 months after ablation in 75 patients verified the absence of accessory-pathway conduction in all. Complications of radiofrequency-current application occurred in three patients (1.8 percent): atrioventricular block (one patient), pericarditis (one), and cardiac tamponade (one) after radiofrequency current was applied in a small branch of the coronary sinus. Conclusions Radiofrequency current is highly effective in ablating accessory pathways, with low morbidity and no mortality.

BACKGROUND Cocaine abuse has been implicated as a cause of death due to sudden cardiac arrest. METHODS AND RESULTS We examined the hemodynamic and electrophysiological effects of cocaine administered as a series of 5-mg/kg i.v. boluses coupled with a continuous infusion in anesthetized dogs. Sodium bicarbonate (50 meq i.v.) was administered as a potential antidote in 11 of 15 dogs, and intravenous 5% dextrose was given in the remaining four. In a dose-dependent fashion, cocaine significantly decreased blood pressure, coronary blood flow, and cardiac output; increased PR, QRS, QT, and QTc intervals and sinus cycle length; and increased ventricular effective refractory period and dispersion of ventricular refractoriness. No afterdepolarizations were noted in the monophasic action potential recording. Nonsustained monomorphic ventricular tachycardia occurred spontaneously in two dogs, and sustained ventricular tachycardia could be induced by programmed stimulation at the end of the dosing protocol in five of 11 animals. Sodium bicarbonate promptly decreased cocaine-induced QRS prolongation to nearly that measured at baseline but had no effect on the other electrocardiographic or hemodynamic variables. In one dog, sodium bicarbonate administration was associated with reversion of ventricular tachycardia to sinus rhythm. CONCLUSIONS We conclude that high-dose cocaine possesses negative inotropic and potent type I electrophysiological effects. Sodium bicarbonate selectively reversed cocaine-induced QRS prolongation and may be a useful treatment of ventricular arrhythmias associated with slowed ventricular conduction in the setting of cocaine overdose.

Seventeen patients with coronary artery disease, idiopathic dilated cardiomyopathy or no organic heart disease who presented with incessant ventricular tachycardia (VT) were studied and followed for a mean period of 51 +/- 35 months. In these patients the incessant VT included greater than or equal to 3 episodes of sustained VT at a rate of greater than or equal to 120 beats/min and frequent episodes of nonsustained VT over a 24-hour period. No patient had electrolyte disorder, prolonged QT interval, drug-induced arrhythmia or myocardial infarction less than 2 weeks old. Six patients died within 27 months of follow-up; 4 from sudden death and 2 from acute myocardial infarction. Three of the 11 surviving patients had remission of their VT within 1 week after the diagnosis of incessant VT. In 3 other patients in whom antiarrhythmic drugs were discontinued during follow-up because of adverse effects of the drugs or other medical reasons, 2 were found in remission. In the remaining 5 alive patients, deliberate attempts were made to discontinue the antiarrhythmic drugs; 4 of these patients were found in remission when the drugs were discontinued. Thus, 9 of these patients (53%) with incessant VT had remission over a mean follow-up of 55 +/- 34 months after discontinuation of the antiarrhythmic drugs. The probability of remission in patients surviving incessant VT warrants trials of discontinuation of antiarrhythmic drugs in these patients.

INTRODUCTION: Rapid firing originating within pulmonary veins (PVs) initiates atrial fibrillation (AF). The following studies were performed to evaluate spontaneous PV firing in patients with AF to distinguish focal versus reentrant mechanisms. METHODS: Intracardiac recordings were obtained in 18 patients demonstrating paroxysmal AF. Microelectrode (ME) recordings were obtained from superfused canine PV sleeves (N = 48). RESULTS: Spontaneous PV firing (566 +/- 16 bpm; 127 +/- 6 ms cycle length) giving rise to AF (52 episodes) was observed. Tachycardia-pause initiation was present in 132 of 200 episodes of rapid PV firing and 34 of 52 AF episodes. The pause cycle length preceding PV firing was 1,039 +/- 86 ms following tachycardia (420 +/- 40 ms cycle length). The remaining episodes were initiated following a 702 +/- 32 ms pause during sinus rhythm (588 +/- 63 ms). Spontaneous firing recorded with a multipolar mapping catheter did not detect electrical activity bridging the diastolic interval between the initial ectopic and preceding post-pause sinus beat. Tachycardia-pause initiated PV firing (138 +/- 7 ms coupling interval) in patients correlated with tachycardia-pause enhanced isometric force, early afterdepolarization (EAD) amplitude, and triggered firing within canine PVs. Rapid firing (1,172 +/- 134 bpm; 51 +/- 8 ms cycle length) following an abbreviated coupling interval (69 +/- 12 ms) was initiated in 13 of 18 canine PVs following tachycardia-pause pacing during norepinephrine + acetylcholine superfusion. Stimulation selectively activating local autonomic nerve terminals facilitated tachycardia-pause triggered firing in canine PVs (5 of 15 vs 0 of 15; P < 0.05). CONCLUSIONS: The studies demonstrate (1) tachycardia-pause initiation of rapid, short-coupled PV firing in AF patients and (2) tachycardia-pause facilitation of isometric force, EAD formation, and autonomic-dependent triggered firing within canine PVs, suggestive of a common arrhythmia mechanism.

Background— The purpose of this study was to measure the extent of left atrial–pulmonary vein (LA-PV) connections and determine the relation to PV firing in patients with atrial fibrillation (AF). Methods and Results— Ten close-bipolar (1 mm-spacing) Lasso electrograms were recorded circumferentially around 210 PVs (excluding 2 right middle PVs and 4 left common trunks) in 62 patients with AF. PV firing was provoked by isoproterenol (4 μg/min) and cardioversion of pacing-induced AF. The width of each LA-PV connection was measured in tenths of PV circumference, based on number of continuous close-bipolar Lasso electrode sites required for ablation (10% for each close-bipolar electrode site). One, 2, or 3 to 4 discrete LA-PV connections (discrete connection defined by ablation along 10% to 30% of PV circumference) were present in 18 (9%), 31 (14%), and 32 (15%) of 210 PVs, respectively: 1 broad connection (ablation along continuous 40% to 80% circumference) in 46 (22%) PVs; 1 broad plus other broad or discrete connections in 54 (26%) PVs; and a circumferential connection (ablation along 90% to 100%) in 29 (14%) PVs. Circumferential LA-PV connections were more common in superior than in inferior PVs (20% versus 7%, P P P Conclusions— The extent of LA-PV connections corresponds with arrhythmognesis. The incidence of PV firing increases with progressively wider LA-PV connections (discrete versus broad versus circumferential).

Atrioventricular nodal reentrant tachycardia (AVNRT), the most common form of paroxysmal supraventricular tachycardia, 1 is a fascinating complex of arrhythmias. AVNRT was originally proposed to result from reentry totally confined within the compact atrioventricular (AV) node. 2 3 However, the typical form of AVNRT (slow/fast) is now thought to involve the AV node, a component of atrial myocardium, and at least two atrionodal connections. 4 5 6 7 8 9 10 11 12 13 14 15 16 Much of the current understanding about the components of the reentrant circuit has evolved from the development of ablation procedures, in which one of the atrionodal connections, remote from the compact AV node, is destroyed, eliminating AVNRT without producing AV block. 4 5 6 7 8 9 10 11 12 16 17 18

Application of microwave energy delivered through a probe and a catheter in open- and closed-chest dogs to induce atrio-ventricular block is described. Several microwave antennas/catheters with a preferential power deposition at the tip were designed, constructed and tested. These antennas were designed for operation at 2450 MHz. Measurements in saline and tissue-equivalent liquid phantoms showed greatly increased heating at the tips of these antennas. The antenna consisted of flexible coaxial cables (1.78 mm OD) with a thin, semigrid brass sleeve just proximal to the tip. The entire antenna was insulated except for the tip and could be used for recording bipolar electrograms. >

RAO, A., et al.: Unexpectedly High Defibrillation Thresholds in an Active Can Implantable Cardioverter Defibrillator System. This case report describes a patient undergoing defibrillator generator replacement in whom the defibrillation thresholds were significantly higher with a can-active system than with a non-active can system.

Background —The purpose of this study was to characterize the circuit of macroreentrant right atrial tachycardia (MacroAT) in patients after surgical repair of congenital heart disease (SR-CHD). Methods and Results —Sixteen patients with atrial tachycardia (AT) after SR-CHD were studied (atrial septal defect in 6, tetralogy of Fallot in 4, and Fontan procedure in 6). Electroanatomic right atrial maps were obtained during 15 MacroATs in 13 patients, focal AT in 1 patient, and atrial pacing in 2 patients without stable AT. A large area of low bipolar voltage (≤0.5 mV) involved most of the free wall in all patients and contained 2 to 7 dense scars or lines of double potentials, forming 29 narrow channels (width ≤2.7 cm) between scars in all but 1 patient, who had a single scar and only focal AT. All 15 MacroATs were propagated through narrow channels. Ablation within the channel eliminated all 15 MacroATs with 1 to 3 (median 1) radiofrequency applications. Ablation was performed in 9 other channels identified during MacroAT (5 patients) and in 5 channels identified during atrial pacing (2 patients). Conduction block was obtained across 28 of 29 channels. After ablation, reproducible sustained right AT was not induced in any patient. During follow-up (median 13.5 months), new MacroATs, atrial fibrillation, or palpitations occurred in 3 of 16 patients. Conclusions —MacroAT after SR-CHD requires a large area of low voltage containing ≥2 scars forming narrow channels. Ablation within the channels eliminates MacroAT.

Background Differentiation between ventriculoatrial (VA) conduction over an accessory AV pathway (AP) and the AV node (AVN) may be difficult, especially in patients with a septal AP. Methods and Results A new pacing method, para-Hisian pacing, was tested in 149 patients with AP and 53 patients without AP who had AV nodal reentrant tachycardia (AVNRT). Ventricular pacing was performed adjacent to the His bundle and proximal right bundle branch (HB-RB), initially at high output to capture both RV and HB-RB. The output was then decreased to lose HB-RB capture. The change in timing and sequence of retrograde atrial activation between HB-RB capture and noncapture was examined. Loss of HB-RB capture without change in stimulus-atrial (S-A) interval or atrial activation sequence indicated exclusive retrograde AP conduction. An increase in S-A interval without change in His bundle-atrial interval or atrial activation sequence indicated exclusive retrograde AVN conduction. A change in atrial activation sequence indicated the presence of both retrograde AP and AVN conduction. Para-Hisian pacing correctly identified retrograde AP conduction in 132 of 147 AP patients, including all septal and right free wall APs. Retrograde AVN conduction masked AP conduction in 9 of 34 patients with a left free wall AP and 6 of 9 patients with the permanent form of junctional reciprocating tachycardia. Para-Hisian pacing correctly excluded AP conduction in all 53 patients with AVNRT. Conclusions Para-Hisian pacing reliably identifies retrograde conduction over septal and right free wall APs, but AVN conduction may mask APs located far from the pacing site or with a long retrograde conduction time.