Background: Studies on the physiology of the cardiovascular system suggest that generation of the heart rate (HR) signal is governed by nonlinear dynamics. Linear and nonlinear indices of HR variability (HRV) have been shown to predict outcome in heart failure (HF). Aim of the present study is to assess if a HR-related complexity predicts adverse clinical and cardiovascular events at 1 year in patients implanted with cardiac resynchronization therapy (CRT).
Methods: In sixty patients implanted with CRT (Renewal), 24-hour HR data were retrieved at patient discharge and 1-year follow-up. A set of linear indices of HRV were considered: mean HR, standard deviation of normal beat to normal beat (SDANN), and HR footprint. Two novel nonlinear indices were calculated by means of a specific algorithm (OntoSpace): HR-complexity (HR-Co) and HR-entropy (HR-En). Predictors of adverse clinical outcome (functional class deterioration or major hospitalizations for cardiovascular causes or all-cause mortality) and of HRV recovery were sought by means of multivariate analysis.
Results: HR-Co and HR-En were found to be highly correlated with the other traditional indices of HRV. Lower baseline values of complexity were associated with adverse clinical outcomes (hazard ratio [HR] 0.71; 95% confidence interval [CI] 0.54–0.95; P < 0.02).
Conclusion: Complexity and entropy indices, calculated from 24-hour normal beat to normal beat (RR) intervals well represent patient's autonomic function. In this limited set of data, HF patients with lower baseline complexity-related indices, representing a more compromised autonomic function, present worse clinical outcome at 1-year follow-up.
Ann Noninvasive Electrocardiol 2010;15(4):301–307