Multisite electrode pacing for prevention of atrial fibrillation

There is increasing evidence that single site atrial pacing is beneficial for atrial fibrillation (AF) prevention in sick sinus syndrome. Multisite atrial pacing methods such as dual site right atrial pacing and biatrial synchronous pacing are currently under active evaluation for AF and atrial flutter prevention in patients with or without bradyarrhythmias. Clinical studies have demonstrated that multisite atrial pacing has an incremental benefit as compared with single site right and left atrial pacing. The electrophysiologic rationale for the efficacy of multisite atrial pacing is based on the reduction of global and local atrial activation times during pacing and for closely coupled atrial premature beats. This results in earlier recovery of excitability and decreased conduction delay. Dual site right atrial pacing consisting of simultaneous pacing from the high right atrium and the coronary sinus ostium reduces the activation times in virtually all left and right atrial regions, especially in areas of conduction delay. Multisite pacing methods reduce the ability to initiate AF with atrial premature beats by reducing the window for AF induction and minimizing the dispersion of atrial refractoriness. In our long-term clinical experience including 30 patients with paroxysmal and chronic drug-refractory AF, 78% of the patients were free of AF recurrence at 1 year, 63% at 2 years, and 56% at 3 years. Rhythm control was achieved in 86% of patients during a follow-up period of 3 years. Concomitantly, we observed a marked reduction in need for anticoagulation, type I antiarrhythmic drugs, and cardioversion therapies. There were no coronary sinus lead-related complications during follow-up. After the initial favorable clinical experiences, two major prospective randomized trials (DAPPAF and SYNBIAPACE) are under way in North America and Europe to evaluate quantitatively the beneficial impact of multisite atrial pacing for AF prevention.

Low-energy endocardial defibrillation using dual, triple, and quadruple electrode systems

The feasibility of achieving both universal application of nonthoracotomy leads and low (< or = 15 J) defibrillation energy requirements by optimizing lead system configuration for use with low-output (<30 J) biphasic shock pulse generators was examined. Sixteen patients (mean age 62 +/- 8 years and mean left ventricular ejection fraction of 38 +/- 15%) were included in the study. All patients had either experienced syncope with induced ventricular tachycardia (n = 4) or had documented sustained ventricular tachycardia (n = 7) or ventricular fibrillation (n = 5). Defibrillation threshold testing was performed in 2 stages on different days in these patients. In the first stage, 2 defibrillation catheter electrodes were positioned in the right ventricle and superior vena cava with an axillary cutaneous patch. Fifteen-joule, 10- and 5-J biphasic shocks were delivered across 3 different electrode configurations-right ventricle to superior vena cava, right ventricle to axillary patch, right ventricle to a combination of superior vena cava and axillary patch. In the second stage, an 80-ml can electrode was added subcutaneously in a pectoral location to the previous leads. Configurations compared were the right ventricle to pectoral can, and right ventricle to an "array"-combining superior vena cava, can, and axillary patch leads. The defibrillation threshold was determined using a step-down method. In stage 1, mean defibrillation threshold for the right ventricle to axillary patch (12.7 +/- 5.9 J) and right ventricle to superior vena cava plus axillary patch (9.8 +/- 5.2 J) configurations was lower than the right ventricle to superior vena cava configuration (14.2 +/- 6.4 J, p <0.05). In stage 2, the defibrillation was higher for the right ventricle to pectoral can (9.2 +/- 5.1 J) configuration compared with the right ventricle to the array (5.6 +/- 3.6 J, p < or =0.05). The right ventricle to array had the lowest defibrillation threshold, whereas the right ventricle to pectoral can was the best dual electrode system. Low-energy endocardial defibrillation (< or =10 J) was feasible in 72% of tested patients with > 1 electrode configuration at 10 J, whereas only 53% of successful patients could be reverted at >1 electrode configuration at 5 J (p <0.05). Reduction in maximum pulse generator output to < or =25 J using these electrode configurations with bidirectional shocks is feasible and maintains an adequate safety margin.

Third- and fourth-generation implantable cardioverter defibrillators: current status and future development

Implantable cardioverter defibrillator (ICD) therapy has become the mainstay of therapy for patients with a history of sudden cardiac death or life-threatening ventricular arrhythmias. The current generation of ICDs used for secondary prevention combines features for tachycardia reversion with demand ventricular pacing, antitachycardia pacing, programmable shock therapy, and tachycardia events memory. Although demand pacing and defibrillation is indicated for primary prevention usage of ICDs, the application of antitachycardia pacing modes is more controversial. High energy cardioversion and defibrillation shocks remaining the mainstay of sudden death prevention will be redefined as more effective defibrillation shock modes and lead systems are developed. Fourth-generation ICD systems accomplished a significant reduction of device size and almost universal success using an endocardial lead configuration and pectoral implant. A variety of new directions of ICD therapy in clinical practice such as primary prevention applications and the adjunctive role of antiarrhythmic drug therapy are currently being examined in clinical trials. The concepts underlying initiation of tachyarrhythmias are being studied to develop new approaches to tachycardia prevention. These include rate support, subthreshold stimulation, and multiple site pacing. The current developments of ICD therapy promise continued growth of this technology.

Innovations in pulse generators and lead systems: balancing complexity with clinical benefit and long-term results

Technologic development of implantable cardioverter defibrillators (ICDs) is now in an exponential growth phase, and many new concepts are being examined. Major innovations have occurred in pulse generators and in lead systems. This may increase ICD use for primary and secondary prevention of sudden cardiac death. Pulse generators now include hybrid pacemaker-defibrillators. Clinical data suggest a need for demand pacing in primary and secondary prevention applications, with antitachycardia pacing being most valuable in the latter group. Atrial leads will allow dual chamber sensing, pacing, and defibrillation. Low energy cardioversion with biphasic shocks can enhance shock efficacy in rapid monomorphic ventricular tachycardia and flutter. Modifications of lead design, biphasic shock waveforms, and optimal thoracic electrode location in axillary or pectoral regions will permit lower energy defibrillation and smaller pulse generators with lower maximum energy outputs of < or = 25 joules. Dual chamber sensing will improve detection of atrial flutter or fibrillation. Minimum data storage requirements for tachycardia events in ICDs still need to be defined. Intracardiac electrogram analysis is still in evolution, and better analytic methods are awaited. Lead system development is likely to support generic pacing and defibrillation catheter electrodes for atrial and ventricular application. Advances in thoracic electrode design are in progress, and a variety of intercostal electrodes are being tested. Improvements in lead design with further impact on defibrillation energy requirements have the potential to permit generator miniaturization. Significant technologic improvements in ICD devices are imminent and should improve clinical results, patient safety, and quality of life.

Late results of the left subcostal approach for automatic implantable cardioverter defibrillator implantation

A left subcostal surgical approach was used to implant an automatic implantable cardioverter defibrillator (AICD) in 48 patients with a history of nonfatal cardiac arrest or documented ventricular tachycardia/fibrillation. Electrophysiologic studies before surgery yielded induction of monomorphic or polymorphic ventricular tachycardia in 40 patients, whereas 8 were noninducible. Mean (+/- standard deviation) age was 58 +/- 12 years. Mean ejection fraction was 33 +/- 16%. Thirty patients (63%) had documented coronary artery disease; 14 patients (29%) had previous coronary bypass surgery. The mean intraoperative defibrillation threshold was 13.8 +/- 6.6 J. In 6 patients, an adjunctive right minithoracotomy was used to position 1 patch over the right atrium and thus optimize the defibrillation threshold. Patients with prior exposure to amiodarone and previous coronary bypass surgery had higher defibrillation thresholds at implantation. Two perioperative deaths occurred. There were no infections. Long-term follow-up yielded a 1- and 5-year survival of 0.88 and 0.58, respectively, and a freedom from sudden cardiac death of 1.0 and 0.97, respectively. The nonthoracotomy, left subcostal surgical approach is safe and effective, provides adequate defibrillation thresholds in most patients, and yields long-term survival comparable to other implantation techniques.

Surgery for atrial tachycardia

Atrial flutter is associated with a macro-reentrant loop including an area of slow conduction cryoablation of which prevents atrial flutter to occur. Three patients underwent such intervention. Atrial fibrillation is associated with multiple reentrant circuits (leading circle of Allessie) that requires a critical surface area to perpetuate. We have designed an operation, the corridor operation, which isolate the sinus node and the AV node within a small segment of atrial tissue, to restore the chronotropic function of the sinus node. Nine patients underwent the corridor operation at our institution. There were eight men and one woman. Five had incessant atrial fibrillation and four paroxysmal. One patient had associated mitral valve stenosis and one cardiomyopathy. There were no perioperative complications. Six patients had normal sinus node function postoperatively including all the four patients with documented normal sinus node function preoperatively. Three patients required implantation of an AAI pacemaker. Two patients had recurrence of atrial fibrillation within the corridor. Our experience suggests that the corridor operation should be restricted to patients with documented good sinus node function and without structural heart disease. Our experience with five patients with paroxysmal sinus node tachycardia has been disappointing. Only one patient had long-term success although better series have been published.

Skeletonization of the atrioventricular node for AV node reentrant tachycardia: experience with 32 patients

We describe our experience with operative therapy for atrioventricular (AV) node tachycardia using an anatomically guided procedure. The operative rationale was to dissect the AV node from most of its atrial inputs (AV node "skeletonization") with the intent of altering the perinodal substrate and preventing reentry. The anteroseptal and posteroseptal regions were initially approached epicardially to facilitate identification of anatomical structures. Under normothermic cardiopulmonary bypass, the right atrial septum was mobilized and the intermediate AV node was exposed anterior to the tendon of Todaro. Atrioventricular node conduction was monitored electrocardiographically throughout the procedure. Ablation of concomitant accessory pathways was done prior to AV node skeletonization. Thirty-two patients aged 9 to 67 years (mean age, 30 years) underwent operation. Five patients had concomitant accessory pathways in addition to AV node reentry. At electrophysiological study before discharge, no patient had AV block although anterograde and retrograde Wenckebach cycle lengths were significantly prolonged. Six patients had retrograde AV block. Twenty-nine patients are free from arrhythmia and require no antiarrhythmic medication after a follow-up of 1 month to 45 months (mean follow-up, 17 months). Three patients had recurrence of tachycardia ten days, 2 months, and 7 months postoperatively. All patients subsequently had a successful reoperation.

Transannular cryoablation of ventricular tachycardia. Surgical technique and results

Intraoperative mapping and cryoablation of ventricular tachycardia was achieved without ventriculotomy in seven patients, who are a subgroup of the 80 patients undergoing map-directed ablation of ventricular tachycardia over a 9-year period. There were four male and three female patients. Their mean age was 53.6 +/- 24.1 years. Coronary artery disease was present in five patients, and two patients had idiopathic ventricular tachycardia. The mean preoperative ejection fraction was 42.4% +/- 13.6%. The mean number of ventricular tachycardia morphologies was 1.7 (range 1 to 3). Epicardial mapping was obtained intraoperatively in all seven patients and endocardial data in five of seven patients (71.4%). There were no hospital deaths and no early or late spontaneous recurrence of clinical monomorphic ventricular tachycardia. Nonclinical monomorphic ventricular tachycardia was inducible in two patients postoperatively and both were treated with procainamide. Death occurred late after operation in two patients: One death was related to recurrent nonclinical VT at 8 months and one at 3 months was due to carcinoma of the stomach. These results suggest that the transannular approach is feasible in selected cases, especially when computerized mapping systems with endocardial balloon electrode arrays can be used.

Right mini-thoracotomy: an adjunct to left subcostal automatic implantable cardioverter defibrillator implantation

High defibrillation thresholds are encountered in some patients during implantation of the automatic implantable cardioverter defibrillator (AICD). In a consecutive series of 52 patients with AICD implants, 46 had allepicardial implants by left subcostal thoracotomy, and 8 of these patients had thresholds greater than 30 J. Placement of an apicolateral large left ventricular patch and an extrapericardial large right atrial patch electrode through a limited right thoracotomy produced substantial reduction in their thresholds. Especially in patients who have had previous intrapericardial operations, this technique provides a simple solution to the problem of high thresholds.