Hyperdynamic performance of remote myocardium in acute infarction

Abstract

During and after myocardial infarction (MI), compensatory contractile and structural changes taking place in the remote uninvolved myocardial regions have been well described, in both experimental and clinical settings. However, quantitative information on the changes in perfusion in these regions in relation to their altered contractile function have not been available. This study was designed to assess the in vivo relationship between contractile function and perfusion in remote uninvolved hypercontractile myocardial regions, subtended by angiographically normal coronary arteries in patients with MI and single-vessel coronary artery disease. We utilized two-dimensional echocardiography and 15O-water positron emission tomography imaging to assess regional contractile function and myocardial blood flow, respectively. Measurements were performed in nine patients with single-vessel coronary artery disease and angiographically confirmed recanalization of the infarct-related artery, 1-2 days after MI (group A). Only patients demonstrating severely impaired wall motion of the infarcted area and reactive hypercontractility of the remote uninvolved regions were enrolled. Seven patients with previous non-reperfused MI (6-8 months post-MI) served as a control (group B). Systolic wall thickening and regional myocardial blood flow data sets were created for the remote myocardial segments perfused by angiographically detected patent coronary arteries by assigning regions on the tomograms to equivalent echocardiographic segments. In the remote regions, wall thickening and regional myocardial blood flow were higher in group A patients by 26% (43 +/- 6% vs 34 +/- 4%; P = 0.005) and 20% (1.06 +/- 0.15 vs 0.89 +/- 0.06 ml.g-1 per minute; P = 0.019), respectively. For both groups of patients, a significant correlation (r = 0.67; P = 0.004) between systolic wall thickening and regional myocardial blood flow was obtained. Infarcted regions in both groups showed no systolic wall thickening. In this selected group of patients these data demonstrate: (1) a proportionate increase in contractility and regional myocardial blood flow in uninvolved territories in patients with recent and old MI; (2) the in vivo relationship between contractile function and myocardial perfusion in man in these regions. When infarcted zones in both groups are equally affected, enhanced levels of catecholamines and sympathetic drive as well as different loading conditions may account for the hyperkinetic performance and consequently for the increased perfusion level in uninvolved segments in patients with recent MI.