beta-blockade improves adjacent regional sympathetic innervation during postinfarction remodeling

The effect of beta-blockade on left ventricular (LV) remodeling, when added to angiotensin-converting enzyme inhibition (ACEI) after anterior myocardi al infarction (MI), is incompletely understood. On day 2 after coronary lig ation-induced anteroapical infarction, 17 sheep were randomized to ramipril (ACEI, n = 8) or ramipril and metoprolol (ACEI-beta, n = 9). Magnetic reso nance imaging was performed before and 8 wk after MI to measure changes in LV end-diastolic, end-systolic, and stroke volume indexes, LV mass index, e jection fraction (EF), and regional percent intramyocardial circumferential shortening. I-123-labeled m-iodobenzylguanidine (MIBG) and fluorescent mic rospheres before and after adenosine were infused before death at 8 wk post -MI for quantitation of sympathetic innervation, blood flow, and blood flow reserve in adjacent and remote noninfarcted regions. Infarct size, regiona l blood flow blood flow reserve, and the increase in LV mass and LV end-dia stolic and end-systolic volume indexes were similar between groups. However , EF fell less over the 8-wk study period in the ACEI-beta group (-13 +/- 1 1 vs. -22 +/- 4% in ACEI, P < 0.05). The ratio of adjacent to remote region I-123-MIBG uptake was greater in ACEI-beta animals than in the ACEI group (0.93 +/- 0.06 vs. 0.86 +/- 0.07, P < 0.04). When added to ACE inhibition a fter transmural anteroapical MI, beta-blockade improves EF and adjacent reg ional sympathetic innervation but does not alter LV size.