Autonomic imbalance in the recovery period after myocardial infarction

The aim of the study was to evaluate the responses to autonomic function tests during the healing period of myocardial infarction (AMI). In 24 patients, at 2 and 6 weeks after the acute event, Valsalva manoeuvre, deep breathing at 6 breaths per min, isometric handgrip and cold pressor tests were performed. Responses of arterial blood pressure (BP) and heart rate (HR) were measured. At 2 weeks post AMI a significant decrease in parasympathetic tone was noted: HR reduction during deep breathing: 18.5 ± 5.7 beats. min^-1 for controls vs 9.7 ± 2.6 beats. min^-1 for AMI, P<0.001. Systolic BP response to handgrip and cold pressor test was only slightly (non significantly) increased: 30.6 ± 12.9 mmHg (controls) vs 40.0 ± 20.5 mmHg (AMI) for the handgrip test and 13.8 ± 8.1 mmHg vs 18.0 ± 10.1 mmHg respectively for the cold pressor test. At 6 weeks post AMI, the response to the deep breathing test (15.9 ± 5.6 beats . min^-1) no longer significantly differed from that in controls. In contrast, the sympathetic stressor tests showed a significant increase in systolic BP response: 63.8 ± 21.9 mmHg, P<0.007 and 26.1 ± 14.9 mmHg, P<0.05, respectively for the handgrip and cold pressor tests. It appeared that infarct localization had no effect on autonomic function tests. There is evidence of autonomic imbalance both at 2 and at 6 weeks after AMI, with a rapid but transient decrease in vagal activity and enhancement of orthosympathetic nervous tone; this was markedly more pronounced at 6 weeks post AMI despite treatment with beta-blocking agents in all patients.