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1 Cardiovascular Division, Department of Medicine, University of Minnesota Medical School, Minneapolis, Minnesota 55455; and 2 Laboratory for Experimental Cardiology, Thoraxcenter, Erasmus University, 3000 DR Rotterdam, The Netherlands
Pressure-overload left ventricular (LV) hypertrophy (LVH) is
associated with increased vulnerability to subendocardial hypoperfusion during exercise. Abnormal perfusion could be the result of failure of
the coronary vessels to grow in proportion to the degree of myocyte
hypertrophy or could be due to increased extravascular forces acting on the intramural coronary vasculature. This
study assessed the contribution of extravascular forces by examining the effect of exercise on the distribution of myocardial blood flow
when coronary vasomotor tone was abolished with a maximal vasodilating
dose of intracoronary adenosine. One year after ascending aortic
banding in six dogs, the LV-to-body weight ratio was 7.80 ± 0.38 g/kg compared with 4.57 ± 0.20 g/kg in nine normal dogs (P < 0.01). Under awake resting
conditions blood flow in LVH hearts increased from 1.17 ± 0.27 ml · min
1 · g
1
during basal conditions to 5.78 ± 1.06 ml · min
1 · g
1
during adenosine (at a coronary pressure of 100 ± 6 mmHg), whereas in normal dogs blood flow increased from 1.22 ± 0.17 to 5.26 ± 0.71 ml · min
1 · g
1
(at a coronary pressure of 62 ± 4 mmHg). At rest the transmural distribution of blood flow during adenosine was not different between
hypertrophied and normal hearts, with subendocardial-to-subepicardial (Endo-to-Epi) blood flow ratios of 1.01 ± 0.09 and
1.14 ± 0.13, respectively (P = not
significant). During adenosine infusion, treadmill exercise to produce
heart rates of 200-220 beats/min caused redistribution of blood
flow away from the subendocardium that was much more marked in LVH
(Endo-to-Epi blood flow ratio = 0.35 ± 0.04) than in normal hearts
(Endo-to-Epi blood flow ratio = 0.76 ± 0.09, P < 0.05 vs. LVH). In comparison
with normal, the exaggerated decrease in subendocardial blood flow
produced by exercise in LVH hearts resulted from abnormally increased
extravascular compressive forces, including a greater decrease in
diastolic duration and an increase in LV end-diastolic pressure.
coronary artery; extravascular compressive forces; adenosine; diastole; subendocardium
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