Dual-Chamber Versus Single-Chamber Detection Enhancements for Implantable Defibrillator Rhythm Diagnosis

Inappropriate implantable cardioverter-defibrillator shocks in MADIT II: frequency, mechanisms, predictors, and survival impact

OBJECTIVES

This study sought to identify the incidence and outcome related to inappropriate implantable cardioverter-defibrillator (ICD) shocks, that is, those for nonventricular arrhythmias.

BACKGROUND

The MADIT (Multicenter Automatic Defibrillator Implantation Trial) II showed that prophylactic ICD implantation improves survival in post-myocardial infarction patients with reduced ejection fraction. Inappropriate ICD shocks are common adverse consequences that may impair quality of life.

METHODS

Stored ICD electrograms from all shock episodes were adjudicated centrally. An inappropriate shock episode was defined as an episode during which 1 or more inappropriate shocks occurred; another inappropriate ICD episode occurring within 5 min was not counted. Programmed parameters for patients with and without inappropriate shocks were compared.

RESULTS

One or more inappropriate shocks occurred in 83 (11.5%) of the 719 MADIT II ICD patients. Inappropriate shock episodes constituted 184 of the 590 total shock episodes (31.2%). Smoking, prior atrial fibrillation, diastolic hypertension, and antecedent appropriate shock predicted inappropriate shock occurrence. Atrial fibrillation was the most common trigger for inappropriate shock (44%), followed by supraventricular tachycardia (36%), and then abnormal sensing (20%). The stability detection algorithm was programmed less frequently in patients receiving inappropriate shocks (17% vs. 36%, p = 0.030), whereas other programming parameters did not differ significantly from those without inappropriate shocks. Importantly, patients with inappropriate shocks had a greater likelihood of all-cause mortality in follow-up (hazard ratio 2.29, p = 0.025).

CONCLUSIONS

Inappropriate ICD shocks occurred commonly in the MADIT II study, and were associated with increased risk of all-cause mortality.

Prevention of inappropriate therapy in implantable defibrillators: A meta-analysis of clinical trials comparing single-chamber and dual-chamber arrhythmia discrimination algorithms

INTRODUCTION

A proposed benefit of dual-chamber arrhythmia discrimination is a reduction in inappropriate therapy in implantable cardioverter-defibrillators (ICDs). The aim of this meta-analysis was to establish whether dual-chamber arrhythmia discrimination algorithms reduce inappropriate device therapy.

METHODS AND RESULTS

Public domain databases, MEDLINE, EMBASE, and Cochrane Register of Controlled Trials, were searched from 1996 to 2006. Two investigators abstracted data independently. Pooled estimates were calculated using both fixed-effects and random-effects models. We retrieved 5 prospective studies comparing dual-chamber with single-chamber arrhythmia discrimination, accumulating data on 748 patients. Pooled per-patient based analysis demonstrated that the number of patients receiving inappropriate ICD therapy was not different between single- and dual-chamber devices (odds ratio [OR] 1.23; 95% CI, 0.83 to 1.81; p=0.31). Per-episode based analysis demonstrated a favoring benefit for dual-chamber arrhythmia discrimination (OR 0.64; 95% CI, 0.52 to 0.78; p<0.001). A mean reduction of 1.1 inappropriately treated atrial episodes per patient was observed with dual-chamber arrhythmia discrimination (p<0.001).

CONCLUSIONS

Dual-chamber arrhythmia discrimination is associated with a reduction in the number of inappropriate treated episodes. The number of patients who experience inappropriate therapy is not reduced by dual-chamber discrimination.

Intramyocardial Pacing and Sensing for the Enhancement of Cardiac Stimulation and Sensing Specificity

BACKGROUND

Intracardiac electrodes create an "antenna" capable of unintentionally recording and stimulating tissue beyond the chamber in which they are positioned, resulting in far-field R wave oversensing in pacemakers and inappropriate detection in defibrillators. This feasibility study sought to determine whether a specially constructed lead with two distal totally intramyocardial electrodes could overcome these limitations.

METHODS

Two mongrel dogs were anesthetized and a median sternotomy performed. Epicardial intramyocardial pacing and sensing function was assessed and compared to standard active fixation pacing and sensing placed at the same atrial and ventricular sites. Right ventricular pacing was also assessed.

RESULTS

For the novel intramyocardial lead, the average R wave amplitude was 7.2 mV, compared to an average R wave of 8.4 mV for the standard active fixation lead placed at identical ventricular sites; P-waves were also similar. Cross-chamber sensing was present in the ventricle and atrium with the standard lead, and absent with the intramyocardial lead. The average pacing threshold was 0.7 mA at 0.2 ms for the novel lead compared to 1.1 mA for the standard lead. With the standard lead, phrenic stimulation was seen at threshold (cathode distal) and at 3 mA (cathode proximal electrode). No phrenic stimulation was seen with the novel intramyocardial lead despite outputs up to 20 mA at sites located 3-5 mm from the phrenic nerve.

CONCLUSION

Totally intramyocardial pacing is feasible, and results in site-specific pacing and sensing function. This may eliminate far-field signal oversensing and phrenic stimulation in future devices.

[Arrhythmias and cardiac electrophysiology]

In the past few months, numerous articles have been published on arrhythmias and cardiac electrophysiology. As in previous years, a substantial proportion of researchers have concentrated on atrial fibrillation, both on catheter ablation of chronic and paroxysmal atrial fibrillation and on the development of new approaches to thromboembolism prophylaxis. The feasibility of atrial fibrillation ablation by remote control has been demonstrated and a step-wise approach to ablation has been proposed, which appears to improve outcome and reduce lesion size. In addition, multicenter randomized trials have shown that the improvements in functional class and left ventricular ejection fraction achieved by ablation in patients with chronic atrial fibrillation are greater than those resulting from pharmacological treatment. New strategies are being developed to improve the selection of patients for defibrillator implantation and to decrease the number of high-energy discharges occurring during follow-up. Controlled trials continue to demonstrate that pharmacological therapy is of little value in preventing recurrence of vasovagal syncope compared with maneuvers involving isometric muscular contraction. Finally, one of the most significant events in the last year was the publication of new clinical practice guidelines by European and American societies of cardiology. These provide important recommendations on the treatment and prevention of ventricular arrhythmias and sudden death and on the management of and thromboembolic prophylaxis in atrial fibrillation.

Design and analysis issues in cardiac arrhythmia trials: insights from the Detect Supraventricular Tachycardia Trial

Background The Detect Supraventricular Tachycardia (Detect SVT) trial was a randomized single blind study in subjects receiving a dual chamber implantable cardioverter defibrillator (ICD). The primary goal was to evaluate whether dual chamber enhancements result in greater discrimination between supraventricular tachycardia (SVT) and ventricular episodes when compared to ventricular-only enhancements.

Purpose The purpose of this report is to describe our experiences from an analytic perspective, including overall study design, the value of blinded episode review, and the statistical analysis plan.

Methods The Detect SVT study was a parallel group study, with blinded central review of all arrhythmia episodes occurring over a six-month period. The primary response was the proportion of inappropriate detections (SVT episodes that are inappropriately classified as ventricular by the device).

Results A parallel group design was essential as unplanned crossovers were very differential. The blinded review of episodes was a major use of resources, with over 2300 episodes observed. This review did not materially alter the findings, however, the avoidance of any perceived bias was a major strength. The value of collecting large numbers of episodes on a single subject was found to be minimal. A Kaplan–Meier analysis of the number of SVT episodes until first inappropriate detection was found to add additional information.

Limitations The recommendations reported here relate to cardiac arrhythmia trials, or other studies with very similar endpoints. These observations are based on the results of a single trial and should be confirmed in other studies.

Conclusions The parallel group design was essential, as was accounting for within-subject correlation in the analysis. The blinded review process was also important, but significant resources could be saved by closing-out episode collection after a fixed number of episodes. Lessons learned from the Detect SVT trial may prove useful to others designing trials in this active research area.

Improving SVT Discrimination in Single-Chamber ICDs: A New Electrogram Morphology-Based Algorithm

INTRODUCTION

Wide-spread adoption of ICD therapy has focused efforts on improving the quality of life for patients by reducing "inappropriate" shock therapies. To this end, distinguishing supraventricular tachycardia from ventricular tachycardia remains a major challenge for ICDs. More sophisticated discrimination algorithms based on ventricular electrogram morphology have been made practicable by the increased computational ability of modern ICDs.

METHODS AND RESULTS

We report results from a large prospective study (1,122 pts) of a new ventricular electrogram morphology tachycardia discrimination algorithm (Wavelet Dynamic Discrimination, Medtronic, Minneapolis, MN, USA) operating at minimal algorithm setting (RV coil-can electrogram, match threshold of 70%). This is a nonrandomized cohort study of ICD patients using the morphology discrimination of the Wavelet algorithm to distinguish SVT and VT/VF. The Wavelet criterion was required ON in all patients and all other supraventricular tachycardia discriminators were required to be OFF. Spontaneous episodes (N = 2,235) eligible for ICD therapy were adjudicated for detection algorithm performance. The generalized estimating equations method was used to remove bias introduced when an individual patient contributes multiple episodes. Inappropriate therapies for supraventricular tachycardia were reduced by 78% (90% CI: 72.8-82.9%) for episodes within the range of rates where Wavelet was programmed to discriminate. Sensitivity for sustained ventricular tachycardia was 98.6% (90% CI: 97-99.3%) without the use of high-rate time out.

CONCLUSIONS

Results from this prospective study of the Wavelet electrogram morphology discrimination algorithm operating as the sole discriminator in the ON mode demonstrate that inappropriate therapy for supraventricular tachycardia in a single-chamber ICD can be dramatically reduced compared to rate detection alone.