Severity in myocardial dysfunction contributed to long-term fluctuation of heart rate, rather than short-term...

It is known that heart rate shows complex behavior, long-term fluctuation of heart rate, and short-term fluctuations in heart failure. Analyzing these properties and examining the relationship to the disease, severity may increase the understanding of the background of heart rate variability (HRV).

In 61 patients (mean age 65 +/- 9 years, 32 ischemic heart disease, 29 cardiomyopathy), with myocardial dysfunction, 24-hour ambulatory electrocardiography was performed. After the construction of the time series of R-R intervals, 15 HRV parameters were measured, including mean heart rate, standard deviation of N-N intervals (SDNN), ratio of low frequency/high frequency power (LF/HF), HRV triangular index (TI), and ratio of length/width at the 90% level of all scattered points.

By using the multiple regression analysis, we tested which HRV parameter (HR, SDNN, LF/HF, TI, or length/width) independently correlated with left ventricular ejection fraction (EF) or left ventricular diastolic dimension (EDD). The results demonstrated that TI and SDNN independently correlated with EF (multiple R = 0.59). Moreover, TI and SDNN independently correlated with EDD (multiple R = 0.45).

TI and SDNN were indicators of the disease severity in myocardial dysfunction, while LF/HF, indicators of autonomic tone, did not have such an ability. It was of interest that the disease severity contributed to long-term fluctuations (TI, SDNN) of heart rate, rather than short-term fluctuations (LF/HF).