Differences in Tachyarrhythmia Detection and Implantable Cardioverter Defibrillator Therapy by Primary or Secondary Prevention Indication in Cardiac Resynchronization Therapy Patients

INTRODUCTION: Although numerous trials have shown benefit of implantable cardioverter defibrillators (ICDs) for either primary or secondary prevention, no trial has prospectively enrolled patients from both indications and analyzed ICD utilization between groups. METHODS AND RESULTS: We performed a retrospective review of MIRACLE ICD, a randomized, prospective double-blind trial of cardiac resynchronization therapy (CRT) in the ICD population. Both secondary prevention (N = 563) and primary prevention patients (N = 415) were enrolled. Subgroup analysis for frequency of ventricular tachycardia (VT) and ventricular fibrillation (VF) episodes and detection accuracy revealed that primary prevention patients had a significantly lower frequency of appropriate episodes (0.09 vs 0.43 episodes/month) at significantly faster cycle lengths (303 +/- 54 ms vs 366 +/- 71 ms, P < 0.0001). These episodes were more likely to be classified as VF by the device and thus receive shock therapy (42% by device classification vs 19% in secondary prevention, P < 0.0001). The absolute rate of inappropriate detections in the primary prevention group per month of follow-up was lower but constituted a much higher proportion of all episodes (30% vs 14%, P < 0.0001). Most inappropriate detections in the secondary prevention group were due to rapidly conducted atrial fibrillation; most in the primary prevention patients were due to sinus tachycardia. CONCLUSION: Patients receiving an ICD for CRT therapy with primary prevention indications have a different clinical arrhythmia course than patients with a history of spontaneous VT/VF. This has implications for the optimal programming of ICDs. Longer-term, prospective evaluation of these differences is warranted and should be investigated in the broader ICD patient population.