Changes in blood pressure and heart period variability in patients with recent acute myocardial infarction.

Abstract

1. A decreased heart period variability and baroreflex sensitivity in patients with acute myocardial infarction have already been documented. Since one of the major determinants of heart period variability is blood pressure variability, it would be important to know the characteristics of blood pressure regulation in this setting. The changes in blood pressure variability during the acute phase of myocardial infarction have not yet been studied. 2. We investigated the blood pressure variability and the heart period variability in 11 patients with acute myocardial infarction 3 to 5 days after their admission. Thirteen age matched patients with no evidence signs of ischaemic heart disease or previous myocardial infarction served as controls. We used the frequency domain indexes of short term measurements of finger blood pressure variability and heart period variability. The spectral powers for both heart period variability and blood pressure variability were divided into three major components: total frequency (0.01-0.4 Hz), low frequency (0.04-0.15 Hz) and high frequency (0.15-0.4 Hz). 3. All of the frequency-domain components of the heart period variability were significantly decreased in patients with recent acute myocardial infarction compared to the controls: Ln(total power): 5.68 +/- 0.24 vs. 7.21 +/- 0.29, Ln(low-frequency power): 4.31 +/- 0.28 vs. 7.05 +/- 0.53, Ln(high-frequency power): 3.50 +/- 0.33 vs. 5.48 +/- 0.32. Acute myocardial infarction patients showed a significantly reduced blood pressure variability in all frequency components compared to the controls: Ln(total power): 4.21 +/- 0.18 vs. 6.79 +/- 0.48, Ln(low-frequency power): 2.40 +/- 0.24 vs. 4.36 +/- 0.21, Ln(high-frequency power): 3.31 +/- 0.25 vs. 5.66 +/- 0.38. 4. We hypothesize that the reduced blood pressure variability in the acute phase of myocardial infarction could be related to a relative invariance of stroke volume. The underlying mechanism is the reduced left ventricular compliance.