Background-Delivery of inappropriate shocks caused by misdetection of supraventricular tachycardia (SVT) remains a substantial complication of implanted cardioverter/defibrillator (ICD) therapy. Whether use of optimally programmed dual-chamber ICDs lowers this risk compared with that in single-chamber ICDs is not clear. Methods and Results-Subjects with a clinical indication for ICD (nϭ400) at 27 participating centers received dual-chamber ICDs and were randomly assigned to strictly defined optimal single-or dual-chamber detection in a single-blind manner. Programming minimized ventricular pacing. The primary end point was the proportion of SVT episodes inappropriately detected from the time of programming until crossover or end of study. On a per-episode basis, 42% of the episodes in the single-chamber arm and 69% of the episodes in the dual-chamber arm were due to SVT. Mortality (3.5% in both groups) and early study withdrawal (14% single-chamber, 11% dual-chamber) were similar in both groups. The rate of inappropriate detection of SVT was 39.5% in the single-chamber detection arm compared with 30.9% in the dual-chamber arm.

No abstract

on behalf of the INTRINSIC RV Study InvestigatorsBackground-Elevated heart rate (HR) is associated with adverse cardiovascular events and total mortality in the general population and in individuals with heart disease. Our hypothesis was that mean HR predicts total mortality and heart failure hospitalization in patients undergoing implantable cardioverter-defibrillator (ICD) implantation. Methods and Results-The Inhibition of Unnecessary RV Pacing With AV Search Hysteresis in ICDs (INTRINSIC RV) trial included 1530 patients undergoing ICD implantation. After implantation of a dual-chamber ICD, patients were followed for a mean of 10.4 months. The mean HR for 1436 patients over the follow-up period was determined from device histograms. Patients were grouped into strata by mean HR, and the relationship between the primary end point and mean HR was analyzed with Mantel-Haenszel ordinal 2 tests. Higher intrinsic (unpaced) HR was associated with greater risk of achieving the primary end point of death or heart failure hospitalization (PϽ0.001). Of patients with a mean HR Ͻ75 bpm, 5.8% died or were hospitalized for heart failure, whereas 20.9% with a mean HR Ͼ90 bpm achieved the same end point, a 3.6-fold difference (PϽ0.0001). In a multivariate model with the use of Cox regression, HR was a significant predictor with a hazard ratio of 1.34 (Pϭ0.0001; 95% confidence interval, 1.19 to 1.50), as were age, New York Heart Association functional class, and percent right ventricular pacing, but it was independent of gender and ␤-blocker dosing. When considered as continuous or discrete variables grouped by 5-bpm increments, HR remained a significant predictor. Conclusions-In this ICD population, the mean intrinsic HR was strongly associated with outcomes. Clinical Trial Registration-http://www.clinicaltrials.gov.