Electrophysiologic Spectrum of Atrioventricular Nodal Behavior in Patients with Atrioventricular Nodal Reentrant Tachycardia Undergoing Selective Fast or Slow Pathway Ablation

AV Nodal Behavior After Ablation. Introduction; The objective of this report is to delineate the atrioventricular (AV) nodal electrophysiologic behavior in patients undergoing fast or slow pathway ablation for control of their AV nodal reentrant tachycardia (AVNRT).
Methods and Results: One hundred sixteen consecutive patients with symptomatic AVNRT were included. Twenty-two patients underwent fast pathway ablation with complete abolition of AVNRT in all and development of complete AV block in five patients. Of 17 patients with intact AV conduction postablation, 12 had demonstrated antegrade dual pathway physiology during baseline study, which was maintained in three and lost in nine patients postablation. Two patients with successful fast pathway ablation developed uncommon AVNRT necessitating a slow pathway ablation. Twenty-one patients demonstrated both common and uncommon forms of AV nodal reentry during baseline study. The earliest site of atrial activation was close to the His-bundle recording site (anterior interatrial septum) during common variety and the coronary sinus ostium (posterior interatrial septum) during the uncommon AV nodal reentry in all 21 patients. Ninety-six patients underwent successful slow pathway ablation. Among these, the antegrade dual pathway physiology demonstrable during baseline study (60 patients) was maintained in 25 and lost in 35 patients postablation.
Conclusion: These data suggest that: (1) dual pathway physiology may persist after successful ablation, which might be a reflection of multiple reentrant pathways in patients with AVNRT: and (2) the retrograde pathways during common and uncommon AVNRT have anatomically separate atrial breakthroughs. These findings have important electrophysiologic implications regarding the prevailing concept of the AV nodal physiology in patients with AVNRT.     

Correlation of Spontaneous and Induced Premature Atrial Complexes Initiating Atrial Fibrillation in Humans: Electrophysiologic Parameters for Guiding Therapy

INTRODUCTION: The low frequency of spontaneous premature atrial contractions (PACs) may be an impediment to mapping and ablation of atrial fibrillation (AF). It has been shown that PACs following external or internal cardioversion of AF can initiate AF. If this method could reproducibly induce PACs from the same location as spontaneous PACs, it would be clinically significant. High-resolution noncontact mapping can map a single beat, should help identify the sites of spontaneously occurring PACs and PACs induced following cardioversion of spontaneous or induced AF, and could help correlate the trigger sites for AF induction. METHODS AND RESULTS: Twelve patients (8 men and 4 women; mean age 49+/-10 years) with spontaneous PACs were included in the study. In all patients, AF was induced and subsequently cardioverted to assess and map isolated PACs or PACs that induced AF. Using the EnSite 3000 noncontact mapping system, mapping was performed of spontaneously occurring isolated PACs and PACs that induced AF and PACs (both with and without AF) that occurred on at least two different occasions following cardioversion. The locations of the spontaneous and the induced PACs were similar; 97% of induced PACs came from the same locations as those of spontaneous PACs (P = 0.5). Radiofrequency lesions guided by this mapping technique were delivered at 14 pulmonary vein sites. Following a single ablation attempt during a mean follow-up of 19+/-4 weeks, 42% of the patients were in sinus rhythm and drug-free, whereas an additional 24% of patients could be maintained in sinus rhythm on drugs that had failed before. CONCLUSION: There is a high degree of correlation between spontaneous and induced PACs as the trigger sites for AF initiation. Cardioversion of spontaneous or induced AF could be used as an electrophysiologic parameter for guiding therapy.     

Right Side Implant of the Unipolar Single Lead Defihrillation System

The active can defibrillator has been designed for implantation in the left prepectoral region. Whether this system can be successfully implanted on the right side is unknown. We describe six cases in which placement of the unipolar single lead defibrillation system was successfully attempted in the right prepectoral region due to impediments on the left side. The mean age of the patients was 62 ± 12 years. Five patients had is–chemic heart disease and one idiopathic dilated cardiomyopathy. The endocardial defibrillation electrode was placed in the right ventricle through the right subclavian vein and positioned at the apex in two patients and in the septal position in four patients. Defibrillation threshold testing was performed using a step-up/step-down protocol beginning at 12 J with 3-J increments or decrements. Defibrillation threshold was defined as the lowest energy of the first shock able to terminate ventricular fibrillation. The generator models used were the Medtronic 7218C in 1 patient, the Medtronic 7219C in 3 patients, and the Ventritex Cadet 115 AC in 2 patients. The mean defibrillation threshold was 15 ± 3 J. The defibrillation thresholds were retested at 1,3, and 6 months, and showed no significant change in five patients but decreased from 15 J to 12 J in one patient. The presence of impediments on the left side should not preclude attempts to place the unipolar active can system in the right prepectoral region.     

The Effect of Biphasic Waveform Tilt in Transvenous Atrial Defibrillation

Atrial defibrillation can be accomplished using low energy shocks and transvenous catheters. The biphasic waveform tilt required to achieve optimal atrial defibrillation thresholds (ADFTs) is, however, not known. The effect of single capacitor biphasic waveform tilt modification on ADFT was assessed in 20 patients. Following AF induction the defibrillation pulses were delivered between the catheters positioned in the coronary sinus and the right atrium.
The single capacitor biphasic waveform shocks, delivered over the same pathways, consisted of 65% tilt (65/65 biphasic waveform) to produce an overall tilt of 88%, or 50% tilt (50/50 biphasic waveform) to produce an overall tilt of 75%. Although 65/65 biphasic waveform delivers more energy, the shorter duration 50/50 biphasic waveform reduced stored energy ADFT 21%, from 1.34 ± 0.82 J with 65/65 biphasic to 2.06 ± 0.81 J. These differences were not statistically significant. Nine patients had lower ADFT with 50/50 biphasic waveform while five patients had lower ADFT with 65/65 biphasic waveform. Equivalent reduction in ADFT was seen in the remaining six patients. The ADFT was 0.83 ± 0.65 J when both tilts were considered. In conclusion, biphasic waveform tilt modification may affect the ADFT in an individual patient. The optimal biphasic waveform for ADFT is not known.     

Comparison of Biphasic and Monophasic Pulses: Does the Advantage of Biphasic Shocks Depend on the Waveshape?

With present implantable defibrillators, the ability to vary the defibrillation technique has been shown to increase the number of patients suitable for transvenous system. As newer waveforms become available, the need for a flexible device may change. In addition, although it has been shown that the option of biphasic waveform may increase the defibrillation efficacy, this may depend upon the shape of the biphasic waveform used. Thirty patients undergoing transvenous defibrillator implant were included in the study. In 20 patients (group I), defibrillation efficacy of simultaneous monophasic, sequential monophasic, and biphasic waveform with 50% tilt was determined randomly. Similarly, in ten patients (group II) testing of simultaneous monophasic shocks and biphasic waveforms with 65% and 80% tilt was performed in random order. The electrode system used consisted of two transvenous leads and a subcutaneous patch in all 30 patients. In group I, 50% tilt biphasic waveform consistently provided similar or better defibrillation efficacy compared to monophasic waveforms (biphasic 7.5 ±5.1 joules vs simultaneous 17 ± 7.8 joules, P < 0.01; and vs sequential 17 ± 8.4 joules, P <0.01). In group II, 65% tilt biphasic pulse required less energy for defibrillation as compared with simultaneous monophasic shocks (9.6 ± 4.5 joulesvs 15.6 ± 5.1 joules, P = 0.04). No significant difference was observed in terms of defibrillation threshold between 80% tilt biphasic shocks and simultaneous monophasic pulses (11.8 ± 6 joules vs 15.6 ±5.1 joules, P = NS). Biphasic shocks with smaller tilt delivered using a triple lead system more uniformly improved defibrillation threshold over standard monophasic waveforms.     

Delivery of Noncommitted Shocks for Nonsustained Ventricular Arrhythmias by a New Implantable Cardioverter Defibrillator with Abortive Shock Capability

Shock Delivery Despite Abortive Shock Capability. Introduction: To describe the delivery of noncommitted implantable cardioverter defibrillator (ICD) shocks despite self-termination of ventricular arrhythmias. Abortive shock capability should eliminate the delivery of shocks for self-terminating ventricular arrhythmias. The delivery of noncommitted shocks despite abortive shock capability is, therefore, unexpected and previously unreported.
Methods and Results: Among 118 patients who received the Transvene nonthoracotomy lead system and the Jewel ICD (model 7219D), three patients (1.7%) experienced spurious, noncommitted shocks for self-terminating arrhythmias. Only one detection zone (i.e., ventricular fibrillation) had been programmed in the defibrillator in each patient. In all three patients, the ventricular arrhythmias self-terminated during the charging period. One patient received seven shocks during periods of asystole, and the other two patients received one shock each. Two different mechanisms for shock delivery in this setting were identified: one occurring in the absence of electrical activity at the end of the bradycardia escape interval (i.e., associated with bradyarrhytbmias), and the other when two sensed electrical events (i.e., escape beats) occurred during the so-called "synchronization" window of the defibrillator.
Conclusions: In rare patients with the Jewel defibrillator, shocks may be delivered for self-terminating arrhythmias despite abortive shock capability. Patients who are dependent upon pacing from their implanted defibrillator are at particular risk for shock in the aftermath of self-terminating ventricular arrhythmias. Defibrillator programming strategies aimed at eliminating or diminishing the incidence of this problem are discussed.     

Pacing Lead Implantation Without Live Fluoroscopy: Feasibility of Acute Success in the Live Canine Model

Introduction: Fluoroscopic visualization for transvenous pacing lead placement necessitates lead shielding to minimize radiation exposure. An electromagnetic (EM) navigation system that integrates real-time intracardiac tracking within an anatomic navigation environment may provide an effective alternative for lead delivery that obviates live fluoroscopy. We assessed feasibility of pacing lead implantation with electromagnetic tracking guided solely by radiographic virtual navigation and compared this to fluoroscopy-guided implants in a canine model.
Methods: Seven mongrel dogs with normal hearts were randomized to 47 pacing lead placements in the right atrium (RA) or right ventricle (RV) guided by single-plane fluoroscopy, or an experimental EM navigation system guided by registered fluoroscopic snapshots obtained before implant (EMN). Ability to achieve successful lead delivery acutely was assessed, and pacing parameters as well as fluoroscopy and implant times were measured. Means were compared using a paired t -test.
Results: All lead delivery attempts were acutely successful. One atrial lead dislodged with EMN, resulting in 46 successful pacing attempts. There was no statistical difference in pacing parameters and time for lead placement between the approaches (EMN vs fluoroscopic navigation [mean ± SD]: RA threshold 1.15 V ± 0.98 V vs 1.95 V ± 0.98 V [P = NS], RV threshold 1.18 V ± 0.58 V vs 1.42 V ± 0.63 V [P = NS], implant time 4:38 ± 2:37 minutes vs 4:44 ± 2:38 minutes [P = NS]). No live fluoroscopy was required for EMN implants.
Conclusion: Pacing lead placement with an EM system guided by preprocedural fluoroscopic views is feasible and comparable to fluoroscopic navigation, and avoids the use of live fluoroscopy.     

Bundle Branch Reentrant Ventricular Tachycardia:

Sustained Bundle Branch Reentrant Tachycardia. introduction: The clinical, electrophysiologic features and follow-up of 48 patients with inducible bundle branch reentrant (BBR) tachycardia are presented. Methods and Results: Forty-eight patients were identified in whom a diagnosis of BBR tachycardia was made during electrophysiologic evaluation. The clinical presentation was syncope or sudden death in 38 patients, and sustained palpitations during wide QRS complex tachycardia in 5 patients. Electrophysiologic studies were performed in 5 additional patients for various other reasons. Structural heart disease was present in 45 patients. Idiopathic dilated cardiomyopathy and coronary artery disease were the anatomical substrates in 19 (39%) and 24 (50%) patients, respectively, severe aortic regurgitation was present in 2 patients, and no organic heart disease was identified in 3. All 48 patients had evidence of His-Purkinje system disease. BBR tachycardia with left and right bundle branch block morphologies was induced in 46 and 5 patients, respectively, and interfascicular BBR tachycardia was initiated in 2 patients. Ventricular tachycardia of a myocardial origin was induced in 11 patients. Management of BBR tachycardia included transcatheter bundle branch ablation in 28 patients, and antiarrhythmic drug therapy in 16 patients. Four patients were treated with implantablc defibrillators. After a mean follow-up of 15.8 months in 42 patients, there were 13 deaths due to congestive heart failure, 4 sudden cardiac deaths, 3 nonsudden cardiac deaths, and 3 noncardiac related deaths. Conclusion: Sustained BBR, a form of monomorphic ventricular tachycardia, is a highly malignant arrhythmia usually seen in patients with structural heart disease. Three different types of BBR tachycardia are described. If distinguished from ventricular tachycardia of a myocardial origin, catheter ablation of the right bundle branch can be easily performed and effectively eliminates BBR. During follow-up, congestive heart failure is the most common cause of death in this population.     

Cardiac Pacing During Neurocardiogenic (Vasovagal) Syncope

Cardiac Pacing and Neurocardiogenic Syncope. Head-up tilt testing is increasingly being used as a diagnostic modality in patients with unexplained syncope who are thought to have neurocardiogenic (vasovagal) mechanisms of syncope. Although large-scale placebo-controlled trials are still awaited, pharmacologic therapy is usually effective in preventing syncope or presyncope in this patient population. However, the role of permanent pacemaker therapy remains controversial. Because hypotension is usually associated with paradoxical bradycardia and occasionally asystole, it has been argued that permanent pacemaker therapy may be useful in preventing syncope and, thus, injury, in the so-called "malignant vasovagal cardioinhibitory response" in which the onset of syncope is thought to be abrupt. The onset of hypotension, however, usually precedes bradycardia during neurocardiogenic syncope, and pacing may thus not prevent syncope or presyncope in these patients. The role of cardiac pacing in patients with neurocardiogenic syncope is reviewed.     

A Case of Flecainide-Induced Hyponatremia

We present a case of flecainide-induced hyponatremia in a 67-year-old woman who was treated for paroxysmal atrial tachycardia. She developed dizziness after starting flecainide and was found to be hyponatremic with a sodium level of 122 mmol/L (decreased from 136 mmol/L). Work-up failed to reveal other causes of hyponatremia. She was not on diuretics, laxatives, or herbal medications. After discontinuation of flecainide, her symptoms and sodium levels improved. Hyponatremia is a previously unrecognized entity as an adverse effect of flecainide. We will discuss the clinical presentation, lab findings, and a possible explanation for this patient's unusual reaction to flecainide.