Background: Diminished heart rate variability is associated with less favorable prognosis after myocardial infarction. However, the prognostic value of early (first 48 hours) measurement and the influence of thrombolytic strategies, myocardial infarction location, left ventricular function, ST-segment shift, and infarct-related artery patency on heart rate variability have not been examined comprehensively.
Methods and results: Heart rate variability and ST-segment analysis of 48-hour Holter tapes were performed with the use of a commercial system in 204 patients who were part of an ST-monitoring substudy of the Global Utilization of Streptokinase and TPA for Occluded Arteries (GUSTO-I) trial. Both time-domain measures (SD of the average normal RR interval for all 5-minute segments of a 24-hour ECG recording [SDANN] and percent difference between adjacent normal RR intervals > 50 ms computed over the entire 24-hour ECG recording [pNN50]) and frequency-domain measures (low frequency [LF], high frequency [HF], and LF/HF ratio) were assessed on days 1 and 2 after acute myocardial infarction. Coronary angiography performed within the first 24 hours was also available in 75% of the patients. All heart rate variability measures decreased between day 1 and day 2 (P = .001) except the LF/HF ratio. There was no difference in heart rate variability among groups assigned to one of four different thrombolytic treatment strategies (streptokinase/subcutaneous heparin, streptokinase/intravenous heparin, accelerated tissue plasminogen activator, and combination streptokinase/tissue plasminogen activator). Heart rate variability measures were lower in anterior versus nonanterior infarcts (SDANN, 53 +/- 21 versus 63 +/- 24 ms; P < .005) and increased with TIMI grade 3 flow (LF, 5.3 +/- 1.0 versus 4.8 +/- 1.2 ms2; P < .01) and better ejection fraction (r = .2, P < .03). An inverse correlation between the duration of ST shift and frequency domain measures was observed (LF, r = -.2, P < .009; HF, r = -2, P < .03). Lower LF/HF ratio by 24 hours after myocardial infarction was seen in those who ultimately died at 30 days (1.0 +/- 0.2 versus 1.3 +/- 0.2, P < .001) or at 1 year (1.17 +/- 0.14 versus 1.26 +/- 0.19, P = .05).
Conclusions: Changes in heart rate variability occurred early after thrombolysis and may be of prognostic value. Heart rate variability measures were improved in patients with better ejection fraction and greater angiographic patency. This suggests a possible mechanism for the enhanced survival observed with TIMI grade 3 flow in the GUSTO angiographic substudy. These data indicate that early heart rate variability assessment after myocardial infarction may be useful in noninvasive risk stratification.