Thrombolytic Therapy Preserves Vagal Activity Early after Acute Myocardial Infarction

Abstract

Objective - The purpose of this study was to evaluate the effects of thrombolytic therapy on vagal tone after acute myocardial infarction (AMI). Design - Holter monitoring for 24 h was performed at hospital discharge and 6 weeks after AMI in 74 consecutive male survivors of a first AMI, who fulfilled established criteria for thrombolytic therapy. Thirty-five patients received thrombolyses, while the remaining 39 patients did not (controls). In each Holter recording 24-h heart rate variability was calculated as pNN50, which represents the percentage of successive RR interval differences >50 ms. Alterations in pNN50 are known to reflect changes in vagal tone. Results - The analysis showed that controls early after AMI had low pNN50 values without any diurnal changes. Six weeks after AMI pNN50 values in controls exhibited a circadian rhythm with higher values during night-time. This pattern was similar to the pattern observed in thrombolysed patients early after AMI. In thrombolysed patients pNN50 values, particularly at night, were further improved 6 weeks after AMI (p = 0.037). Conclusion - These observations indicate that thrombolytic therapy, given for a first AMI, preserves vagal activity when compared with patients who are not thrombolysed. The enhanced parasympathetic tone may be a part of the beneficial mechanisms responsible for the reduction in mortality after thrombolysis in AMI.