HEART-RATE-VARIABILITY IN THE EARLY HOURS OF AN ACUTE MYOCARDIAL-INFARCTION

The occurrence of an autonomic disturbance early in acute myocardial i nfarction (AMI) has been reported: signs of sympathetic activation wer e mainly observed in relation to an anterior localization, whereas sig ns of vagal overactivity were more frequent in inferior wall AMI. Info rmation is limited in relation to the persistence of these alterations during the early hours of AMI. We studied 33 patients with an AMI wit hin 188 +/- 16 minutes from the onset of symptoms and 1 week after hos pital admission. From a 20-minute Holter recording, we computed with a utoregressive methodology, time and frequency domain indexes of heart rate variability. At admission, patients with an anterior wall AMI exh ibited a smaller RR variance (593 +/- 121 ms(2)) than did those with a n inferior wall AMI (1,122 +/- 191 ms(2)). In both groups the spectral profile was characterized by a predominant (73 +/- 4 and 61 +/- 4 nor malized units) low frequency and by a small (13 +/- 2 and 22 +/- 3 nor malized units) high-frequency component, indicating the presence of a sympathetic excitation and of a diminished vagal modulation. Although signs of sympathetic activation were more evident in patients with ant erior wall AMI, no evidence of a vagal hyperactivity was observed in p atients with inferior wall AMI. In the latter group, we noticed 1 week after the acute event an increase in the low-frequency component, whi ch reached the values observed in patients with anterior wall AMI. Thr ombolysis did not affect heart rate variability parameters. Thus, this study suggests the presence of an autonomic disturbance characterized by signs of sympathetic excitation and of a reduced vagal modulation, which was more evident in patients with an anterior localization earl y after AMI.