ASSESSMENT OF AUTONOMIC FUNCTION IN PATIENTS WITH ACUTE MYOCARDIAL-INFARCTION BY HEART-RATE SPECTRAL-ANALYSIS

Sympathovagal interaction was assessed by analysis of spectral components of heart rate variability in patients after acute myocardial infarction. The indices of the time and frequency domain of heart rate variability were compared with some prognostic risk variables like radionuclide left ventricular ejection fraction, New York Heart Association functional class, duration of exercise test, ventricular arrhythmias on 24-hour Holter recordings, age and localization of infarction. Forty-eight patients were studied: 24 postinfarction patients aged 56 (+/- 8) years - group 1 - and 24 control subjects aged 52 (+/- 10) years - group 2. Power spectral density was calculated by fast Fourier transform of 512 consecutive sinus beats after 15 min at rest in the supine position. The subjects breathed in synchrony with a metronome at 15 breaths/min. The RR average interval was 732.5 +/- 106.1 and 841.3 +/- 122.6 ms (p < 0.05), and R-R corrected standard deviation was 12.8 +/- 5.5 and 36.8 +/- 8.3 ms (p < 0.001) in groups 1 and 2, respectively. In group 1, the low-frequency spectral component (LF: 0.05-0.15 HzEq) was very decreased (0.03 +/- 0.02 s2) and the high frequency (HF: 0.15-0.50 HzEq) was virtually absent (0.01 +/- 0.01 s2) compared with group 2 (0.16 +/- 0.05 and 0.15 +/- 0.09 s2, respectively), p < 0.001. Nevertheless, the ratio LF/HF was increased in postinfarction patients compared with control subjects (2.66 +/- 0.58 and 1.23 +/- 0.61, respectively), p < 0.05. The indices of heart rate variability had a bad correlation with the prognostic risk variables studied; the strongest correlation was with left ventricular ejection fraction (Pearson r = 0.66). These results suggest that the spectral pattern in postinfarction patients had low LF and HF power density; the decreased heart rate variability in that group is mainly due to diminished parasympathetic activity (HF component) in cardiac regulation. The indices of the time and frequency domain of heart rate variability in the short-term had a bad correlation with some prognostic variables.