Decreased heart rate variability(HRV) has been shown to be an independent predictor of poor outcome after acute myocardial infarction, Spectral analysis of HRV has recently been shown to be a reliable noninvasive test for quantiative assessment of cardiovascular autonomic regulatory response. We estimated the reproducibility and circadian rhythm of HRV parameters in patients with acute myocardial infarction.

Three consecutive 24-hour ambulatory electrocardiographic recordings were made in 24 patients with acute myocardial infarction, with 10~14 days after the acute attack, and analyzed for HRV parameters of both frequency and time domains. Parameters of frequency domain include low frequency(LF) and high frequency(HF) components. Parameters of time domain include sdRR, SDANN, SD, pNN50, rMSSD, HRV index.

Mean total, low frequency and high frequency amplitude spectral densities were 33msec, 19msec and 11msec, respectively. Mean values of sdRR, SDANN, SD, rMSSD, pNN50 and HRV index were 103msec, 90msec, 47msec, 28msec, 7% and 32, respectively. Coefficients of variation(CV) of total amplitude spectral density, and low and high frequency components were 7%, 9% and 12%, respectively. CV of most HRV parameters of time domain were also around 10% except rMSSD and pNN50. Heart rate increased in the morning to be sustained during the day time and decreased in the night. Heart rate variability of high frequency component decreased in the early morning to be sustained during day time with increase in the night.

We conclude that in the predischarge period of acute myocardial infarction, HRV parameters of frequency and time domains are reproducible and there are some morning fall of cardiac vagal activity.