Renin-angiotensin-aldosterone system, RR-interval and blood pressure variability during postural changes after myocardial infarction

Low frequency (LF, 0.04-0.15 Hz) and high frequency (HF, 0.15-0.40 Hz) components of heart rate variability have been used to evaluate the autonomic nervous system. The sympathico-vagal balance as well as the renin-angiotensin-aldosterone (RAA) axis are disturbed in the post-acute phase of acute myocardial infarction (AMI). This study examined the relationship between the RAA-axis and spectral indices of the RR-interval and blood pressure (BP) variabilities during postural manoeuvres in the post-AMI period. Power spectral analysis of the RR-interval and BP variability was computed with non-invasive beat-to-beat BP measurements 10-12 days post-AMI, using Fast-Fourier transforms. Concomitantly, hormonal changes of the RAA-axis were determined and data were further correlated with the left ventricular ejection fraction. When the patient moved from the lying to the supine position all RAA-axis parameters significantly increased. Both LF and HF components of total RR-interval variability decreased on standing, while the LF component of systolic and diastolic BP variability increased and HF components remained constant. In the upright position, plasma renin activity (P<0.01) and angiotensin II (borderline) were inversely related with the LF component of systolic BP. The aldosterone level was dissociated from plasma renin activity and angiotensin II. The left ventricular ejection fraction was inversely correlated (P<0.05) with systolic and diastolic BP variabilities and their LF and HF powers. These results suggest that the renin-angiotensin II system in the post-acute phase of AMI patients treated with aspirin and β-blocking agents is correlated with cardiovascular autoregulation during postural manoeuvres.