Thrombolytic therapy preserves vagal activity early after acute myocardial infarction

The purpose of this study was to evaluate the effects of thrombolytic therapy on vagal tone after acute myocardial infarction (AMI).

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.

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).

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.