Thrombolytic therapy preserves vagal activity early after acute myocardialinfarction

Objective-The purpose of this study was to evaluate the effects of thrombol ytic 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 fulfi lled established criteria for thrombolytic therapy. Thirty-five patients re ceived 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 val ues without any diurnal changes. Six weeks after AMI pNN50 values in contro ls 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, we re 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 be neficial mechanisms responsible for the reduction in mortality after thromb olysis in AMI.