REGIONAL MYOCARDIAL BLOOD-FLOW IN LEFT-VENTRICULAR HYPERTROPHY - AN EXPERIMENTAL INVESTIGATION IN NEWFOUNDLAND DOGS WITH CONGENITAL SUB-AORTIC STENOSIS

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  • 1 January 1982
    • journal article
    • research article
    • Vol. 84  (6) , 876-885
Abstract
Left ventricular hypertrophy (LVH) may predispose the subendocardium to ischemia. Regional myocardial blood flow in dogs with the fibrous ring form of subvalvular aortic stenosis and concentric LVH was studied. Radioactive microspheres, 9 .+-. 1 .mu.m in diameter, were used. Dogs (11) with LVH (left ventricular/body wt ratio of 6.35 .+-. 0.46 g/kg [mean .+-. SEM] and peak left ventricular outflow gradient of 51 .+-. 7 mm Hg) were compared to normal dogs (12) (left ventricular/body wt ratio of 3.41 .+-. 0.12 g/kg and peak left ventricular outflow gradient of 6 .+-. 3 mm Hg). The 2 groups of dogs were subjected to comparable experimental interventions including tachycardia produced by atrial pacing (221 .+-. 4 beats/min), ascending aortic constriction producing systolic hypertension (212 .+-. 5 mm Hg) and creation of an aorta-right atrial fistula lowering diastolic blood pressure (38 .+-. 3 mm Hg). Basal regional myocardial blood flow was distributed similarly for LVH and normal dogs (endocardial/epicardial ratio = 0.90 .+-. 0.05 and 0.94 .+-. 0.03, respectively). During experimental interventions, regional blood flow remained equal to all myocardial layers in normal dogs; however, the endocardial/epicardial ratio diminished in LVH dogs during atrial tachycardia to 0.61 .+-. 0.08, during systolic hypertension to 0.68 .+-. 0.06, and during diastolic hypotension to 0.50 .+-. 0.09. When the diastolic/systolic pressure time index ratio (DPTI/SPTI) was < 0.8, subendocardial ischemia occurred in dogs with LVH (endocardial/epicardial ratio = 0.66 .+-. 0.04) but not in normal dogs (endocardial/epicardial ratio = 0.92 .+-. 0.03) (P < 0.0001). Animals with infracoronary obstruction and LVH demonstrte greater susceptibility to development of subendocardial ischemia for identical hemodynamic interventions than do normal animals.