HEART-RATE-VARIABILITY DURING THE ACUTE PHASE OF MYOCARDIAL-INFARCTION

Background. After acute myocardial infarction (AMI), several abnormalities of the autonomic control to the heart have been described. Heart rate (HR) variability has been used to explore the neural control to the heart. A low HR variability count measured 7-13 days after AMI is significantly related to a poor outcome. Little information is available on HR variability early after AMI and its relation to clinical and hemodynamic data. Methods and Results. We studied 54 consecutive patients (42 men and 12 women; mean age, 60.4+/-11 years) with evidence of AMI by collecting the 24-hour HR SD from Holter tapes recorded on day 2 or 3. We also measured HR variability in 15 patients with unstable angina and in 35 age-matched normal subjects. HR variability was lower in AMI than in unstable angina patients (57.6+/-21.3 versus 92+/-19 msec; p<0.001) and controls (105+/-12 msec; p<0.001). Also, HR variability was greater in non-Q-wave than in Q-wave AMI (p<0.0001) and in recombinant tissue-type plasminogen activator-treated patients with respect to the rest of the group (p<0.02). No difference was found for infarct site. HR variability was significantly related to mean 24-hour HR, peak creatine kinase-MB, and left ventricular ejection fraction (all p<0.0001). Patients belonging to Killip class >I or who required the use of diuretics or digitalis had lower counts (p<0.004, p<0.001, and p<0.024, respectively). Six patients died within 20 days after admission to the hospital. In these patients, HR variability was lower than in survivors (31.2+/-12 versus 60.9+/-20 msec; p<0.001), and a value <50 msec was significantly associated with mortality (p<0.025). Conclusions. HR variability during the early phase of AMI is decreased and is significantly related to clinical and hemodynamic indexes of severity. The causes for the observed changes in HR variability during AMI may be reduced vagal and/or increased sympathetic outflow to the heart. It is suggested that early measurements of HR variability during AMI way offer important clinical information and contribute to the early risk stratification of patients.