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-Blockade improves adjacent regional sympathetic
innervation during postinfarction remodeling
1 Division of Cardiology,
The effect of
-blockade on left ventricular (LV) remodeling, when added to
angiotensin-converting enzyme inhibition (ACEI) after anterior
myocardial infarction (MI), is incompletely understood. On
day 2 after coronary ligation-induced
anteroapical infarction, 17 sheep were randomized to ramipril (ACEI,
n = 8) or ramipril and metoprolol
(ACEI-
, n = 9). Magnetic resonance
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,
ejection fraction (EF), and regional percent intramyocardial
circumferential shortening.
123I-labeled
m-iodobenzylguanidine (MIBG) and
fluorescent microspheres 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, regional blood flow, blood flow reserve, and the
increase in LV mass and LV end-diastolic and end-systolic volume
indexes were similar between groups. However, EF fell less over the
8-wk study period in the ACEI-
group (
13 ± 11 vs.
22 ± 4% in ACEI, P < 0.05). The ratio of adjacent to remote region
123I-MIBG uptake was greater in
ACEI-
animals than in the ACEI group (0.93 ± 0.06 vs. 0.86 ± 0.07, P < 0.04). When added to ACE
inhibition after transmural anteroapical MI,
-blockade improves EF
and adjacent regional sympathetic innervation but does not alter LV size.
magnetic resonance imaging; myocardial infarction; remodeling; myocardial contraction
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