Changes in autonomic tone following thrombolytic therapy for acute myocardial infarction: assessment by analysis of heart rate variability.

INTRODUCTION

Little data are available on changes in autonomic tone during the first 24 hours of acute infarction in patients undergoing thrombolytic therapy. Particularly, the association of changes in autonomic tone to reperfusion of the infarct-related artery has not been evaluated in man. Heart rate variability (HRV) is a noninvasive tool to assess cardiac autonomic tone, which carries prognostic information in postinfarction patients.

METHODS AND RESULTS

To assess changes in autonomic tone with angiographically assessed success of thrombolysis in patients with acute infarction, the proportion of adjacent RR intervals different by greater than 50 msec (pNN50) was analyzed from 24-hour Holter monitoring initiated before the start of thrombolytic therapy in 103 consecutive patients. Mean heart rate (HR) and pNN50 were available in 95 of 103 patients and were separately analyzed for the first hour after initiation of thrombolysis (reperfusion phase) and the first 24 hours. As assessed by coronary angiography 90 minutes after start of thrombolysis, 74 patients (78%) had successful coronary artery reperfusion. HR averaged 72 +/- 13/min for the first hour in all 95 patients and 74 +/- 13/min for the first 24 hours. The respective values for pNN50 were 11.2% +/- 11.7% for the first hour and 9.7% +/- 9.2% for the first 24 hours. Patients with inferior myocardial infarction (MI) had a lower mean HR of 72 +/- 12/min versus 76 +/- 13/min (P = 0.11) and a higher pNN50 (11.2% +/- 9.8% versus 7.6% +/- 8.3%, P = 0.01) compared to patients with anterior MI. The mean HR correlated weakly with pNN50 (r = -0.33, P < 0.01). For patients with coronary artery patency after 90 minutes, mean HR was 70 +/- 12/min for the first hour compared to 80 +/- 13/min for patients without (P = 0.003). For the first 24 hours, these values were 72 +/- 12/min compared to 80 +/- 14/min (P = 0.02). For the first hour, pNN50 averaged 12.6% +/- 12.4% for patients with successful reperfusion compared to 6.6% +/- 7.3% for patients without (P = 0.024). For the first 24 hours, these values were 9.2% +/- 8.5% compared to 11.5% +/- 11.3% (P = NS). Patients with in-hospital ventricular fibrillation (n = 8) had a higher mean HR throughout the first 24 hours (88 +/- 16/min vs 73 +/- 12/min, P = 0.008) compared to patients with an uneventful course. Additionally, there was a trend toward a lower HRV in patients with ventricular fibrillation.

CONCLUSION

Thrombolysis-induced reperfusion of the infarct-related artery results in a higher vagal tone during the early hours of MI as compared to failed reperfusion. This finding is independent from infarct location and associated with a trend toward a lower incidence of ventricular fibrillation during the acute phase of infarction.