Heart rate variability as an index of sympathovagal interaction after acute myocardial infarction

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Abstract

By analysis of spectral components of heart rate variability, sympathovagal interaction was assessed in patients after acute myocardial infarction (AMI). At 2 weeks after AMI (n = 70), the low-frequency component was significantly greater (69 ± 2 vs 53 ± 3 normalized units [NU], p < 0.05) and the high-frequency component was significantly smaller (17 ± 1 vs 35 ± 3 NU) than in 26 age-matched control subjects. This difference was likely to reflect an alteration of sympathovagal regulatory outflows with a predominance of sympathetic activity. At 6 (n = 33) and 12 (n = 29) months after AMI, a progressive decrease in the low- (62 ± 2 and 54 ± 3 NU) and an increase in the high-frequency (23 ± 2 and 30 ± 2 NU) spectral components was observed, which suggested a normalization of sympathovagal interaction. An increase in sympathetic efferent activity induced by tilt did not further modify the low-frequency spectral component (78 ± 3 vs 74 ± 3 NU) in a subgroup of 24 patients at 2 weeks after AMI. Instead, 1 year after AMI, this maneuver was accompanied by an increase in the low-frequency component (77 ± 3 vs 53 ± 3 NU, p < 0.05) of a magnitude similar to the one observed in control subjects (78 ± 3 vs 53 ± 3 NU). These data indicate that the sympathetic predominance that is detectable 2 weeks after AMI is followed by recovery of vagal tone and a normalization of sympathovagal interaction, not only during resting conditions, but also in response to a sympathetic stimulus.

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