Evolutionary pattern and prognostic importance of heart rate variability during the early phase of acute myocardial infarction

Aims: To investigate the evolution of time domain heart rate variability in the early phase of acute myocardial infarction (MI) and assess its prognos tic ability. Methods: We analysed several measures of heart rate variabilit y (SDNN, SDANN, SDNN index, RMSSD) in 138 patients at days 0, 1 and 5 +/- 1 after hospital admission for acute MI. Results were correlated with infarc t site, clinical variation and clinical outcome (death, MI, PTCA, CABG surg ery). Results: Measures of heart rate variability (SDNN, SDANN and SDNN ind ex) declined during the first 24 h after acute MI (P < 0.01) and increased to admission levels after about 5 days. SDNN values on day 0, 1 and 5 respe ctively were: 86 <plus/minus> 35, 75 +/- 28 and 87 +/- 27 ms. Patients with anterior infarction had lower heart rate variability than patients with in ferior infarction on all test days but similar evolution patterns. After 3 years of follow-up there were 12 cardiac deaths (8.7%) and six resuscitated arrests and 33 (24%) new MIs, or revascularisation procedures. The evoluti onary pattern of heart rate variability was similar in survivors to those w ho died although values were generally lower. Mortality was significantly h igher in the group with SDNN<50 ms at day 1 (P < 0.01) and 5 (P < 0.05), bu t not at day 0. Conclusions: Our findings show that autonomic imbalance, al ready evident on the day of the acute event, progresses further over the ne xt 24 h and recovers over the next few days. Low heart rate variability as early as 24 h after acute MI may be a useful predictor of cardiac mortality and contribute to the early risk stratification and therapeutic management of patients. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.