The Usefulness of the Coefficient of Variation of Electrocardiographic RR Interval as an Index of Cardiovascular Function and its Correlation with Age and Stroke

The coefficient of variation (CV) of the time interval between two consecutive R-waves, also known as the RR interval (RRI), is calculated by dividing the standard deviation of RRI (SDNN) by the mean of RRI. CV of RRI is similar to heart rate variability in terms of individual normalization. The purpose of this study was to evaluate the validity of CV of RRI as an index of cardiovascular function and its correlation with age and stroke. CV of RRI, SDNN, and baroreflex sensitivity (BRS) were evaluated in 31 healthy controls and 25 patients who had suffered ischemic stroke. Resting electrocardiography and arterial blood pressure were recorded for 10 min, once in the supine position in all recruited subjects and once in the head-up tilt position in the controls. BRS was measured using the spontaneous sequence analysis method.In the healthy controls, CV of RRI, SDNN, and BRS recorded in both the supine (r = −0.526, −0.731, and −0.637, respectively; all p ＜ 0.01) and head-up tilt positions (r = −0.785, −0.697, and −0.703, respectively; all p ＜ 0.01) were negatively correlated with age. In contrast, no correlation was found between these indices and age in the stroke patients. Significant correlations were found among CV of RRI, SDNN, and BRS in both the healthy controls and stroke patients (all p ＜ 0.01). In conclusion, CV of RRI measured using simple medical devices may be a potentially useful indicator of cardiovascular function in both healthy individuals and stroke patients. Aging is associated with a decline in SDNN, BRS, and CV of RRI in healthy individuals.