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Antidromic Tachycardia in Patients with an Atriofascicular Fiber. Background: The typical and most common tachycardia in patients with atriofascicular pathways is a macro reentrant tachycardia, with anterograde conduction over the decrementally conducting bypass tract and retrograde conduction over the right bundle branch-His-AV node axis resulting in a short V-right bundle branch and short V-H interval. Objectives: To report on changes in rate and QRS configuration when right bundle branch block (RBBB) develops spontaneously during antidromic tachycardia using an atriofascicular fiber. Methods: Three of 25 patients with an antidromic circus movement tachycardia using a right-sided atriofascicular pathway showed episodes of right bundle branch block (RBBB) during ventriculo-atrial conduction. Effect of retrograde RBBB on tachycardia rate and QRS configuration was studied using intracardiac and extracardiac recordings. Results: All 3 patients showed prolongation of their V-A interval when retrograde RBBB occurred during tachycardia, resulting in a longer tachycardia cycle length. The VA time increase ranged from 85 to 100 msec, with a mean 346 ± 5 msec. Two of the 3 patients also showed a change in QRS configuration due to a more leftward shift of the frontal plane QRS axis. Conclusion: Rate changes in antidromic tachycardia in patients with atriofascicular fibers can be based on a shift in VA conduction from one bundle branch to the other. This may be accompanied by changes in the frontal plane QRS axis because of a change in ventricular activation sequence.

Introduction: Automatic rhythms associated with Mahaim fibers usually occur during radiofrequency catheter ablation. The incidence and significance of spontaneous automaticity in Mahaim fibers are unknown. Methods and Results: Spontaneous automatic rhythms were observed in 5 (12.5%) of 40 patients with Mahaim fibers referred for nonpharmacologic therapy because of recurrent episodes of symptomatic tachyarrhythmias, usually antidromic circus movement tachycardia (33/40 patients). Three were female and two were male. Their mean age was 15 ± 7 years compared to 26 ± 13 years of the patients without automaticity (P = 0.09). Three patients had both antidromic tachycardia and asymptomatic spontaneous automatic rhythms recorded during ambulatory ECG (1 patient) or electrophysiologic study (2 patients). In 2 patients, the automatic rhythm triggered antidromic tachycardia. Two other patients had nonsustained repetitive episodes of wide QRS tachycardia due to automaticity arising in the Mahaim fiber, without antidromic tachycardia. All automatic rhythms were abolished by successful catheter ablation of the Mahaim fibers. Conclusion: Spontaneous automaticity occurred in 12.5% of our Mahaim patients and may trigger antidromic tachycardia. Spontaneous automaticity, which is not seen in rapidly conducting accessory pathways, is another argument for the presence of an AV nodal-like structure in Mahaim fibers. (J Cardiovasc Electrophysiol, Vol. 15, pp. 738-744, July 2004)

Septal Activation in Patients with LBBB and Heart Failure.Introduction: Little is known about the septal activation pattern in patients with heart failure and left bundle branch block (LBBB-HF). Methods and Results: The right ventricular (RV) and left ventricular (LV) activation patterns of 12 patients (mean age 67 ± 11 years) with LBBB-HF and 5 patients (mean age 45 ± 14) with normal hearts were studied during sinus rhythm using a three-dimensional mapping system. The etiology of HF was myocardial infarction (n = 4) or idiopathic dilated cardiomyopathy (n = 8). In patients with LBBB-HF, endocardial activation usually started before the onset of the surface QRS complex on the RV free wall. Latest RV activation occurred in the basal region, and total RV activation time was longer than in patients with normal hearts. In patients with LBBB-HF, the left septum was activated via slowly conducting LBB or via right-to-left transseptal conduction. In both patients with LBBB-HF and those with normal hearts, latest LV activation occurred either in the posterior or posterolateral-basal region. Conduction velocity was slower in the peri-scar region, in patients with previous myocardial infarct and globally slow, in patients with idiopathic dilated cardiomyopathy. Conclusion: The two types of left septal activation observed in patients with LBBB-HF may have consequences for biventricular hemodynamic performance. Conduction slowing along the LV, regionally or globally, suggests a contribution outside the specific conduction system in the ECG pattern of LBBB. (J Cardiovasc Electrophysiol, Vol. 14, pp. 135-141, February 2003)

Atrial Defibrillation Pathway. Introduction: Previous studies have demonstrated significant failure in converting atrial fibrillation (AF) using a conventional ventricular pathway. The aim of this study was to assess the benefit of incorporating a coronary sinus (CS) lead into the atrial defibrillation pathway in atrial defibrillation threshold (ADFT) reduction in patients with persistent AF. Methods and Results: This study was a prospective, randomized assessment of shock configuration on ADFT in 18 patients undergoing elective internal cardioversion for persistent AF (mean AF duration: 8 ′ 9 months). The lead system included a dual-coil defibrillation lead (Endotak DSP, Guidant) with a distal right ventricular (RV) electrode and a proximal superior vena cava (SVC) electrode, a CS lead (Perimeter, Guidant), and a left pectoral cutaneous electrode (Can). In each patient, dual step-up ADFTs were determined for each of three vectors: (1) RV → SVC+Can; (2) CS → SVC+Can; and (3) RV → CS+SVC+Can (group 1, n = 8) or RV+CS → SVC+Can (group 2, n = 10), using R wave-synchronized biphasic shocks. Successful defibrillation was achieved in all patients without any ventricular proarrhythmia. ADFT of CS -> SVC+Can (11.8 ′ 5.6 J) was significantly lower than ADFT of RV → SVC+Can (16.5 ′ 7.8 J, P = 0.021). ADFT of CS → SVC+Can was similar to RV → CS+SVC+Can (group 1: 12.0 ′ 6.5 J vs 17.4 ′ 4.8 J, P = 0.16), but it was significantly higher than RV+CS → SVC+Can (group 2: 9.0 ′ 3.9 J vs 11.6 ′ 5.0 J, P = 0.049). Conclusion: Patients with persistent AF of substantial duration can be reliably cardioverted using a conventional implantable cardioverter defibrillator (ICD) lead set; however, the incorporation of a CS lead to the conventional ICD lead configuration significantly lowered ADFT. The optimal shock vector that incorporates a CS lead for atrial defibrillation requires future studies.

TSE, H.-F., et al.: Effect of Coexisting Cardiovascular Disease on the Long-Term Efficacy and Safety of the Implantable Atrial Defibrillator. The long-term efficacy and safety of implantable atrial defibrillator (IAD) therapy in patients with AF and cardiovascular disease is unclear. The aim of this study was to evaluate the efficacy and safety of IAD therapy in patients with and without coexisting cardiovascular disease. In 115 patients implanted with an IAD, 85 patients had cardiovascular disease: 41 (48%) patients had 1 cardiovascular abnormality, 29 (35%) patients had 2, 13 (15%) patients had 3, and 2 (2%) patients had 4 different cardiovascular abnormalities. The device was programmed into a rhythm monitoring mode for the first 3-month postimplant period. All defibrillation therapy was performed under physician supervision to monitor safety and efficacy. After this initial monitoring period, patients were allowed to activate their device away from the hospital or clinic. A total of 357 spontaneous AF episodes occurred in 83 (72%) patients during observed operation and the mean shock efficacy was 93.5 ± 20.3% (lower 95% confidence interval [CI] 89.8%). As of the last follow-up, 58 (55%) patients had transition to receive nonphysician observed therapy. Forty-two (72%) patients had experienced 332 episodes of AF for which they had received device therapy away from the hospital/clinic (mean shock efficacy 90.5 ± 39.7%). The presence of hypertension, valvular heart disease, and ischemic heart disease did not affect the shock efficacy of the IAD during physician observed and nonobserved therapy (P > 0.05). However, the presence of congestive heart failure was associated with a lower clinical efficacy during observed and nonobserved therapy (P < 0.05). Overall, 5,262 shocks have been delivered with the IAD without any episode of proarrhythmia. The observed proarrhythmic risk was 0%, with an estimated maximum proarrhythmic risk of 0.06% per shock (95% upper CI). A stand-alone IAD appears to be safe in the presence of cardiovascular disease. The lower clinical efficacy for AF associated with congestive heart failure might be related to a higher rate of early reinitiation of AF after defibrillation.

Predictors of Survival in Postinfarct VT. Introduction: The aim of this study was to determine the predictive value of echocardiographic parameters of systolic left ventricular (LV) dysfunction for survival in a group of patients with “mappable” ventricular tachycardia (VT) after myocardial infarction who underwent radiofrequency ablation (RFA) of their clinical VT(s). Methods and Results: RFA of at least one inducible, “mappable,” and clinical VT was attempted in 61 patients. In total, 63 (79%) of 80 target clinical VTs were ablated successfully, such that clinical VT(s) were noninducible in 49 (80%) of 61 patients. At the last recorded follow-up (range 2 to 98 months; mean 21 ± 20), nonfatal VT recurrences were observed in 11 (22%) patients; 10 (16%) patients died. On univariate analysis, a higher LV end-diastolic volume (LVEDV; P = 0.008) and, by multivariate analysis, applying backward selection of variables, older age (P = 0.03) with a higher LVEDV (P = 0.003) predicted patients more likely to die. When age and LV ejection fraction (LVEF) were excluded, LV end-systolic diameter (LVESD; P = 0.007) was the most significant predictor of survival. Conclusion: In our patient population with postinfarct VT who underwent RFA of mappable clinical VT(s), LVEF did not predict survival. In this group of patients with overall low mean LVEF (

Electrode Length for Atrial Defibrillation. Introduction: Catheter-based electrodes have been used previously to terminate episodes of atrial fibrillation in animals and man. Typically, these electrodes span 6 to 7 cm, and lowest energy requirements are achieved when these electrodes are positioned in the distal coronary sinus and in the right atrium. The purpose of this study was to evaluate the use of longer electrode lengths for atrial defibrillation. Methods and Results: In 15 patients, two decapolar catheters were inserted, one into the distal coronary sinus and one in the right atrium. To provide longer electrodes lengths, a third catheter was inserted and alternated positioned in the right atrium or coronary sinus. A 6-cm electrode span was obtained by using the distal 8 rings on the coronary sinus catheter or 8 consecutive electrodes on the right atrial catheter and increased from 6 to 11 cm by connecting consecutive, nonoverlapping rings of the third catheter with the 10 rings of the initial right atrial or coronary sinus catheter. Atrial defibrillation thresholds were determined twice, in a randomized order, in each patient for each of the three combinations of electrode lengths. All 15 patients could he successfully converted to sinus rhythm without complications; however, one patient could be converted reproducibly with only 2 of the 3 electrode combinations. Mean thresholds were 306 ± 102 V, 5.9 ± 4.0 J for the 6 cm/6 cm electrode length combination with an impedance of 72 ± 18 ω. For the electrode combination using the 11-cm electrode in the right atrium, the defibrillation threshold was 296 ± 107 V, 5.8 ± 3.9 J with an impedance of 61 ± 17 ω and was 294 ± 91 V, 5.6 ± 3.6 J with an impedance of 55 ± 11 ω for the 11-cm electrode in the coronary sinus. There were no significant differences in defibrillation voltage or energy (P > 0.05) associated with the longer electrode lengths; however, the longer electrode lengths did significantly lower shock impedance (P < 0.05). Conclusion: The use of longer electrodes, when using the right atrium to coronary sinus shock vector, does not lower the defibrillation requirements for restoration of sinus rhythm.

Sudden death can be the first manifestation of the Wolff-Parkinson-White (WPW) syndrome. The underlying mechanism being atrial fibrillation with a very high ventricular rate, because of a short anterograde refractory period of the accessory atrioventricular pathway (AP), deteriorating into ventricular fibrillation. Information on the anterograde refractory period of the AP is therefore important to recognize asymptomatic people with the WPW ECG at risk for dying suddenly. Several noninvasive tests are available to identify the low risk patient. Decision making when to interrupt the AP in asymptomatic WPW patients not at low risk requires an invasive study to document the electrophysiological properties of the AP and to determine its exact location.

We performed radiofrequency catheter ablation of idiopathic ventricular tachycardia in six children. In four, the ventricular tachycardia originated in the left ventricle, in two it originated in the right ventricular outflow tract. In 5/6 (83%) the RF procedure was successful; there were no complications.

Monomorphic VT in HCM. Introduction: Incessant monomorphic ventricular tachycardia (VT) with a right bundle branch block morphology and a northwest axis is a rare arrhythmic complication in a patient with hypertrophic cardiomyopathy and apical left ventricular aneurysm. Methods and Results: The origin of this VT was localized using the following criteria: the presence of entrainment without fusion, equal internals from the stimulus to the beginning of the QRS complex and from the electrogram to the QRS complex during VT, and the first postpacing interval identical to the tachycardia cycle length. Radiofrequency energy applied to the septoapical part of the apical left ventricular aneurysm terminated the tachycardia within 2 seconds. Conclusion: Using criteria to guide radiofrequency (RF) ablation of VT in patients with coronary artery disease, an incessant monomorphic VT in a patient with hypertrophic cardiomyopathy was successfully ablated.

An atrial defibrillator was implanted in a patient with congenitally corrected transposition of the great arteries, associated cardiac abnormalities, and persistent atrial arrhythmias. During a 15-month follow-up, 14 of 20 spontaneous episodes of his arrhythmias were successfully treated with the device. Two of these episodes were converted to sinus rhythm during ambulatory use of the device. Successful use of the device required implantation of a third defibrillation lead in the persistent left-sided superior caval vein and rigid control of congestive heart failure. An atrial defibrillator may be a valid treatment option in patients with congenital heart disease crippled by atrial fibrillation.