A Device Histogram-Based Simple Predictor of Mortality Risk in ICD and CRT-D Patients: The Heart Rate Score

We hypothesized that survival in implantable cardioverter defibrillator (ICD) and cardiac resynchronization therapy defibrillator (CRT-D) patients is predicted by baseline Heart Rate Score.

Heart Rate Score is determined from the atrial paced and sensed histogram of a DDD ICD or CRT-D, and defined as percent of beats in the histogram in the tallest 10 beats/min range bin. It was calculated at initial remote monitoring for patients enrolled in LATITUDE® without persistent atrial fibrillation, and with pulse generators implanted in 2006-2011. Univariate, multivariate, and Kaplan-Meier analyses determined the impact of Heart Rate Score on survival.

Of 57,893 ICDs and 67,929 CRT-Ds followed for 2.4 ± 1.5 years, each 10% increase in Heart Rate Score was associated with decreased survival (CRT-D hazard ratio [HR] 1.07 95%, confidence interval 1.06-1.07, P < 0.0001; ICD HR 1.05, 95% confidence interval 1.04-1.06, P < 0.0001). Multivariate analysis showed survival decreased with increasing age, atrial fibrillation, presence of a shock in first-year follow-up, and increasing programmed lower pacing rate in ICD and CRT-D patients. Increased percent right ventricular pacing predicted mortality in ICD patients, while male gender and lower percent left ventricular pacing predicted mortality in CRT patients. Heart Rate Score predicted survival independent of those variables. Heart Rate Score correlates with heart rate variability (standard deviation of average R-R intervals [SDANN]) when both are obtainable, but SDANN was only present in 6% of patients with Heart Rate Score >70%.

A simple device histogram measure, Heart Rate Score, predicts survival in ICD and CRT-D patients independent of the available variables, and even when SDANN is unavailable.