Heart rate score predicts mortality independent of shocks in ICD and CRT-D patients.

Background: Heart Rate Score (HrSc), a novel index found to predict mortality in patients with implantable defibrillator (ICD) and cardiac resynchronization defibrillator (CRT-D) devices, is associated with mortality in ICD and CRT-D recipients when HrSc is ≥ 70%. Implantable defibrillator shocks have also been associated with increased mortality in ICD and CRT-D recipients. The objective of this study was to evaluate the relationships between HrSc, shocks, and mortality in ICD and CRT-D patients.
Methods: HrSc was calculated from atrial sensed and paced rate histograms collected from the 2006-2011 ALTITUDE remote interrogation database. Shocks were determined in the first year of follow-up. Mortality was assessed over the next 4 years by the Social Security Death Index. Four multivariable models were run: ICD and CRT-D, shock and no shock, with mortality as the outcome and HrS as predictor.
Results: Data from 49,358 ICD and 55,953 CRT-D patients were divided into HrSc: ≥ 70%, 30-69%, and < 30%. Shock rates differed between HrSc groups (p < 0.001) for ICD and CRT-D patients. However, the lowest mortality risk HrSc (< 30%) had the highest shock rate. Both highest HrSc (> 70%; p < 0.001) and shocks (p < 0.001) predicted mortality during follow-up. Mortality was unrelated to interactions between HrSc and shocks in ICD patients (p = 0.275) or CRT-D patients (p < 0.079). Comparing HrSc ≥ 70% to HrSc < 30%, HrSc ≥ 70% predicted mortality in CRT-D (HR 1.40; 95% CI 1.29-1.52) and ICD (HR 1.23; 95% CI 1.11-1.36) patients regardless of shocks (P < 0.001 for both).
Conclusions: Patients with ICDs or CRT-Ds having the lowest mortality risk HrSc had the highest shock rate. Shocks and HrSc appear to complement each other as predictors of mortality.