REPRODUCIBILITY OF HEART-RATE-VARIABILITY IN THE CHRONIC PHASE OF MYOCARDIAL-INFARCTION

Evaluation of heart rate variability is a common method of assessing a utonomic nervous system function and its effects on heart rate in diff erent conditions. The reproducibility of the technique is not known in the chronic phase of myocardial infarction. The aim of this study was therefore to assess the reproducibility of the measurement in 54 subj ects who were clinically stable with no change in treatment at a dista nce from acute or semi-recent (> 2 years) myocardial infarction, after an interval of one month. The temporal and spectral analysis of heart rate variability included measurement of the standard deviation of th e normal RR intervals (SDNN), on the mean heart rate, the percentage o f RR intervals greater than 50 ms than the adjacent interval (pNN50), the coefficient of variability (CV), the square root of the difference s between successive RR intervals (rMSSD), the power of low frequencie s (LF) and high frequencies (HF) and of the fractional spectral power (LF/HF). No significant changes in these parameters were observed. Ana lysis of individual variations showed that the heart rate was the most stable parameter; for evaluation of vagal tone, the rMSSD showed less variability than the pNN50 and HE The presence of cardiac disease did not influence these results. The authors conclude that parameters of evaluation of heart rate variability in temporal and spectral analysis are globally reproducible in stable subjects. However, individual val ues may change from one measurement to another. Nevertheless, abnormal variability is constantly observed at the second investigation and, s imilarly, normal variability also remains unchanged. These individual variations suggest that, for the demonstration of change in these para meters of variability with treatment, large population groups must be studied.