Implantation of an extravascular defibrillator with a preexisting endocardial dual-chamber defibrillator: When 2 defibrillators share 1 heart

R-wave double counting secondary to antiarrhythmics and ablation leads to unnecessary shock

T he Dual Chamber and VVI Implantable Defibrillator (DAVID) trial randomized 506 patients and tested the hypothesis that the dual-chamber pacing mode would produce improved hemodynamics and would in turn reduce congestive heart failure, heart failure hospitalizations, heart failure deaths, atrial fibrillation, strokes, ventricular arrhythmias, and total mortality compared to backup ventricular pacing in patients indicated for implantable defibrillator therapy. Patients had either primary prevention indications (47%) or secondary prevention indications (53%) for implantable defibrillator therapy but had no indications for bradycardia pacemaker support. All the patients had moderate to severe left ventricular dysfunction with a left ventricular ejection fraction of 40% or less (mean = 27%) and were consistently treated with angiotensin converting enzyme inhibitors or angiotensin II receptor blockers (86%) and beta adrenergic blocking agents (85%). The primary combined endpoint of hospitalization for congestive heart failure or death was paradoxically increased and statistically significant ( p = 0.03) at one year in the patients paced in the dual chamber mode (22.6%) compared to patients randomized to ventricular backup pacing (13.3%). Both heart failure hospitalization and mortality contributed outcome. Another perspective would consider this a randomized controlled study of presence or absence of pacemaker therapy in patients with left ventricular dysfunction and indications for implantable defibrillator therapy. Ventricular backup pacing produced less than 3% ventricular and no atrial pacing, while dual chamber pacing produced approximately 60% atrial and ventricular paced heart beats. The poor outcome in the dual chamber paced group correlated with the percentage of right ventricular pacing and suggests that right ventricular pacing caused ventricular dyssynchrony. The poor outcome associated with right ventricular pacing compared to intrinsic activation in the control group of the DAVID trial is reminiscent of the poor outcome associated with prolonged intraventricular conduction activation in the control groups compared to biventricular pacing in the intervention groups of the cardiac resynchronization trials. The direct conclusion from these results are that patients with indications for implantable defibrillators and no indication for pacing should not be paced in the dual chamber pacing mode. It is not appropriate to conclude that only single chamber implantable defibrillators should be implanted. There are other potential advantages to having an implanted atrial lead including improved secondary outcomes. However the DAVID trial results suggest that the dual chamber paced mode was not associated with improved quality of life or decreased frequency of hospitalization, inappropriate shocks from the defibrillator or atrial fibrillation. The more important question is what is the optimal pacing mode in these patients? The AAIR mode is under investigation in the DAVID II study in an attempt to identify a pacing mode that preserves atrio-ventricular synchrony, normal atrio-ventricular timing, prevents bradycardia and also prevents right ventricular stimulation. Caution should be taken to not directly apply these results to patients with either an indication for pacemaker therapy or to patients with an indication for cardiac resynchronization therapy since patients from neither population were included. However, considering the large magnitude of the deleterious effects associated with dual chamber pacing in the DAVID trial future studies should explore the possibility that left ventricular stimulation may be the only pacing mode capable of preventing bradycardia without increasing death and congestive heart failure.

Stretch the heart: Get memory

The clinical utility of ventricular electrograms in comparison to atrial and ventricular electrograms in diagnosing the type of tachycardias recorded by an implantable defibrillator has not been addressed from the standpoint of a clinician's diagnostic accuracy and confidence in that diagnosis. Fifty-two tachycardia episodes recorded from dual chamber defibrillators were divided into two tests. The initial test contained only information from the ventricular electrogram and the second test contained information from both the atrial and ventricular electrograms. For each test, the reviewers were asked to provide the specific diagnosis, the originating chamber of origin of the tachycardia, and the confidence of their responses for each question. McNemar's test for matched pairs was used to determine accuracy and an analysis of variance to determine reviewer confidence. The overall accuracy for both the specific diagnosis (61% vs. 79%; p < 0.001) and the chamber of origin (76% vs. 90%; p < 0.001) improved when both the atrial and ventricular electrograms were available for review. Reviewer confidence appeared to correlate with diagnostic accuracy. The data clearly show the favorable impact of dual chamber defibrillators on the diagnostic accuracy and confidence of clinicians faced with a clinical tachycardia recorded from an implantable defibrillator. Such improvements may translate into more focused and appropriate therapeutic interventions.

The DAVID (Dual Chamber and VVI Implantable Defibrillator) II Trial

Impact of Atrial Pacing on Quality of Life in the Dual Chamber and VVI Implantable Defibrillator (DAVID) II Trial

Stored atrial and ventricular electrograms retrieved from dual chamber implantable defibrillators facilitate the diagnosis of arrhythmias. This case also illustrates the usefulness of programmed atrial and ventricular stimulation for noninvasive rhythm diagnosis in patients with a wide QRS tachycardia and an implantable defibrillator.

Ventricular safety pacing (VSP) is an algorithm used to prevent crosstalk inhibition and ventricular capture during the vulnerable period. We report a 78-year-old man with implantable dual-chamber defibrillator, in whom clusters of ventricular tachycardias (VTs) were provoked by the VSP. During rapid DDDR pacing, the delivery of the VSP after every other atrial-paced beat resulted in short-long-short ventricular sequences and induced VTs. An atrial-based lower rate timing, long atrioventricular pacing interval, and automatic gain control also accounted for this arrhythmogenic ventricular sequence. The VSP and the subsequent VT were eliminated by decreasing the pacing rate.

The promising results achieved with internal atrial defibrillation have facilitated the development of an implantable atrial defibrillator. Methods: For any new therapy, it is imperative to demonstrate safety, efficacy, tolerability with improvement in quality of life, and cost-effectiveness compared to already available therapeutic options. Most importantly, the efficacy and safety rates with a new therapy should be better or at least as good than those observed with previously available means. Maintenance of sinus rhythm or prolonged duration in arrhythmia-free intervals should be clearly demonstrated with an implantable atrial defibrillator, the MetrixTM system. Recently, a new dual-chamber defibrillator (7250 Jewel AF AMD) has entered clinical evaluation. The most important new features of the 7250 AMD system include: dual-chamber pacing, a new dual-chamber detection criterion for rejection of supraventricular tachycardias, detection and treatment modalities of atrial arrhythmias, prevention strategies for atrial arrhythmias. The dual-chamber detection criterion is constantly monitoring the rhythm in the ventricle as well as in the atrium. This new dual-chamber detection algorithm is used to improve discrimination of ventricular tachycardia from supraventricular tachycardia by applying pattern recognition methods based on different P-wave positions within RR sequences. The detection algorithm can be used to withhold inappropriate ventricular therapies. Results: Initial clinical experience with the MetrixTM system indicates stable atrial defibrillation thresholds, appropriate R-wave synchronization markers, no shock induced ventricular proarrhythmia, and excellent detection of atrial fibrillation with a specificity of 100%. Ventricular proarrhythmia has not been reported for correctly R-wave synchronized low energy shocks when closely coupled RR intervals and long-short cycles are avoided. The first results with the 7250 Jewel AF device suggest a high sensitivity for induced ventricular tachyarrhythmias and an increased specificity for reduction of inappropriate therapies.

Hemodynamic Impact and Outcome of Permanent Pacemaker Implantation Following Transcatheter Aortic Valve Implantation

Third-generation cardioverter-defibrillators have revolutionized management of ventricular tachyarrhythmias. Implantation can be performed in the electro-physiology laboratory, with minimal morbidity. Generator size has shrunk to the point that subcutaneous implantation is feasible and safe, even under local anesthesia. The prepectoral technique, however, is associated with increased mechanical stress to the subcutaneous tissue and can predispose to device erosion or infection. These complications may be avoided by submuscular placement. Among subpectoral techniques, the lateral approach offers unrestricted ability to deploy patches or array electrodes, should the need arise, and may represent the optimal implant technique under some circumstances. We studied 29 male patients, aged 29-78 years, who presented with syncope or sustained ventricular tachycardia, and underwent subpectoral defibrillator implantation under general anesthesia or conscious sedation. All devices were third-generation active can systems with biphasic shock capability. Six dual-chamber defibrillators were used. Subpectoral implantation was successful in all cases, with an estimated blood loss of 28+/-17 mL and no immediate complications. Except for one patient who developed twiddler's syndrome and ultimately required revision to a subcutaneous pocket, the implant site was tolerated well, and no limitation in the range of motion of the upper limb was observed during 20 months of follow-up. Subpectoral implantation using a lateral approach is technically straightforward and can be applied globally, with modest additional resource and equipment requirements. Familiarity with this approach can maximize the likelihood of successful defibrillator implantation in the electrophysiology laboratory.

Time to resumption of driving after implantation of an automatic defibrillator (from the Dual chamber and VVI Implantable Defibrillator [DAVID] trial)

This editorial refers to ‘Reduction in unnecessary ventricular pacing fails to affect hard clinical outcomes in patients with preserved LV function: a meta-analysis’ by M. Shurrab et al. Two studies took away the ‘innocence’ from right ventricular pacing (RVP). The DAVID (Dual-Chamber and VVI Implantable Defibrillator) trial has assessed whether prevention of bradycardia prevents bradycardia-dependent ventricular tachyarrhythmia, initiated by long–short cycles. This trial reported that more patients died or developed heart failure with prevention of bradycardia by dual-chamber implantable cardiverter defibrillators (ICDs) than with single-chamber ICDs that basically did not pace.1 This result prompted calls for ‘the simpler the better’ sounding like a win–win situation: the device that is simpler for the physician to implant and programme is also better for the patient! However, the culprits for worse outcomes in DAVID were not the devices but the physicians who did not reprogramme dual-chamber ICDs and thus caused unnecessary RVP. Death or heart failure hospitalization developed during 18 months in 32% of patients if DDDR resulted in RVP for >40% of the time compared with only 8% if DDDR resulted in RVP for ≤ 40% of the time.2 By definition, RVP was unnecessary in the DAVID trial because patients with an indication for pacing were excluded. The results from DAVID were likely so striking because all patients had heart failure at baseline. These data suggest that RVP accelerates progression of heart failure by inducing ventricular dyssynchrony and should therefore be avoided. The second study that created doubt about the ‘innocence’ of RVP was a post hoc analysis of the MOST (MOde Selection Trial) study. It showed that in patients with sinus node disease and narrow QRS at baseline, unnecessary RVP increased the risk of heart failure hospitalization and atrial fibrillation.3 Of note, patients in MOST had a normal left ventricular ejection …

The discrimination of concomitant atrial tachyarrhythmias and sinus tachycardias in patients with malignant ventricular tachyarrhythmias is a major challenge for new defibrillator devices. Different algorithms have now been established to distinguish between atrial and ventricular tachyarrhythmias. Furthermore, new dual-chamber implantable defibrillators are capable of tiered atrial therapies for both regular and irregular atrial and ventricular tachyarrhythmias. The increasingly complex and subtle dual-chamber detection algorithms have proven to be safe and effective for the detection of ventricular tachycardia, and also in terms of an increase in specificity and a reduction in inappropriate ventricular therapies for supraventricular tachyarrhythmias. Stable electrode position, and a continuous and correct atrial signal quality, are prerequisites for atrial therapies and algorithms for arrhythmia discrimination.

A 38 year old man with a recent large anterior wall myocardial infarction had sustained monomorphic ventricular tachycardia with a rate of 142 beats/min causing palpitations and signs of congestive...