Combined Analysis of Cardiac Repolarization Entropy and Magnetic Resonance Imaging Enhances Risk Stratification of...

Accurate selection of patients who will benefit from a primary-prevention implantable cardioverter-defibrillator (ICD) remains a challenge. Cardiac magnetic resonance imaging (CMR) of myocardial tissue heterogeneity and EntropyX_QT, a nonlinear electrocardiographic (ECG) measure of cardiac repolarization dynamics, predict ventricular tachyarrhythmias (VTs) and sudden cardiac arrest.

Because CMR and EntropyX_QT are fundamentally distinct structural and electrical measures, we hypothesized that they add major independent prognostic value to conventional clinical predictors of sudden cardiac arrest.

In 230 consecutive patients with a left ventricular ejection fraction ≤35% in sinus rhythm, baseline exposures before primary prevention ICD implantation included demographics, history, medications, laboratory results, conventional ECG indices of heart rate and QT variability, CMR myocardial tissue characterization, and EntropyX_QT. The primary endpoint was ICD shock for VT, and secondary endpoints included all-cause events, including mortality.

Over 6.1 ± 3.3 years of follow-up, 62 patients (27%) received appropriate ICD shocks. In multivariable analyses, EntropyX_QT and CMR gray zone mass yielded adjusted hazard ratios (per SD change) of 1.8 (95% CI: 1.4-2.3) and 1.5 (95% CI: 1.2-1.8), respectively, and improved Harrell's C-statistic from 0.59 to 0.73 in a model composed of conventional clinical predictors, left ventricular end-systolic volume (LVESV) and prescribed diuretics. EntropyX_QT was the strongest predictor in years 1-3, whereas CMR and LVESV were stronger in years >3. Moreover, EntropyX_QT independently predicted the secondary endpoints.

EntropyX_QT and CMR gray zone mass complement each other and conventional risk factors, improving risk stratification for appropriate ICD shock and mortality, and together may enhance the selection of primary prevention ICD recipients. (Prospective Observational Study of the ICD in Sudden Cardiac Death Prevention (PROSe-ICD; NCT00733590).