Assessment of autonomic control of the heart during transient myocardial ischemia

IntroductionIn the presence of coronary artery obstruction, complex cardiovascular reflexes may lead to changes in heart rate and even to the precipitation of malignant arrhythmias. The autonomic nervous system (ANS) has traditionally been considered to be “balanced” between continuously interacting sympathetic and parasympathetic outflows. The purpose of this study was to assess ANS control of the heart during prolonged coronary balloon occlusion procedures of one of the major coronary arteries.MethodsR-R intervals were obtained from continuous electrocardiographic data of 90 patients undergoing selective percutaneous coronary interventions (PCI) with balloon inflation periods ranging from 3 to 10 minutes (4.7 ± 1.1 minutes). Three 3-minute stages were chosen: (1) preinflation (baseline), (2) from the start of occlusion (PCI), and (3) immediately post deflation. The dynamics of the ANS was evaluated by heart rate variability analysis using standard time and frequency domain indices and the short-term fractal-like index (α1).ResultsDuring PCI, time and frequency domain measures related to vagal control decreased significantly with respect to baseline (significantly in left anterior descending [LAD] artery occlusions). During the postdeflation stage, heart rate variability and high-frequency power increased (P < .01) in the group with right coronary artery occlusions, whereas a marked sympathetic increase, as assessed by an increase (P < .01) of normalized low-frequency power and the low/high-frequency ratio was observed in the LAD group after balloon deflation. Fractal index α1 decreased during the PCI period but increased significantly after balloon deflation.ConclusionsSignificant changes in autonomic control of heart rate that were a function of the affected artery occurred during and after coronary artery occlusions. Occlusion of the LAD resulted in a significant reduction of vagal activity and a decrease of the short-term fractal index during PCI and a marked sympathetic response after postdeflation. However, a marked increment of vagal activity between the occlusion stage and postdeflation period was found in the right coronary artery group. These results may relate the site of the occlusion and lack of blood supply to different parts of the left ventricle.