[Effect of the location of myocardial infarction on the variability of heart rate: a study during the acute phase].

OBJECTIVES

The influence of the location of acute myocardial infarction on the autonomic tone and its evolution during the first hours post-infarct has not been fully evaluated. The aim of this study was to analyze this effect using a spectral analysis of the heart rate variability.

PATIENTS AND METHODS

Forty-nine consecutive patients with acute myocardial infarction (22 anterior and 27 inferior) in sinus rhythm and free of diseases and drugs which could affect heart rate variability were studied. Five-minute Holter recordings within each hour between 10 and 33 hours after the onset of symptoms were analyzed, calculating the standard deviation of NN intervals and the spectral power of the high and low frequency bands using normalized units.

RESULTS

The standard deviation was higher in inferior infarcts (51.4 +/- 23.4 ms vs. 38.6 +/- 14.8 ms in anterior location; p < 0.05) and gradually decreased over time in both locations. The relative distribution of high- and low-frequency bands did not show significant differences related to the infarct location. An inverse significant correlation between the high-frequency component and time was observed for anterior infarcts (r = -0.98; p < 0.001) as well as in the inferior group (r = -0.75; p = 0.04). Conversely, the low-frequency power gradually increased in anterior infarcts (r = 0.98, p < 0.001) while remaining stable in inferior locations (r = -0.08; NS).

CONCLUSIONS

A gradual reduction of heart rate variability was observed in patients with acute myocardial infarction during the time of monitorization. The spectral analysis suggests that anterior infarcts present a progressive increase of sympathetic activity and a reduction of vagal tone, whereas inferior infarcts show a parallel reduction in both components of the autonomous nervous system.