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212 MYOCARDIAL PERFUSION DURING EXERCISE IN DOGS WITH LEFT VENTRICULAR OBSTRUCTION ABOVE AND BELOW CORONARY ARTERIES

Strenuous exercise is thought to induce global myocardial ischemia in the presence of left ventricular hypertrophy (LVH) and normal coronary arteries. Myocardial perfusion (MBF) and cardiac index (CI) were measured in dogs with chronic LVH due to outflow tract obstruction. LVH was induced by banding the ascending aorta (Sp) in 7 puppies (LV/body weight = 6.6 ± .4 gm/Kg) and plicating the posterior sinus below the coronary ostia (Sb) in 10 puppies (6.4 ± 1.1). Nine to 13 months after surgery, MBF and CI were measured at rest and during treadmill exercise (Ex) using 15u radioactive microspheres. Mean ± SEM heart rates (HR) in beats/min, CI in cc/min/Kg, and anterior left ventricular (ALV) endocardial/epicardial flow ratios (R) in Sp and Sb dogs are as follows:Inferior LVR were not significantly different in Sp and Sb dogs. These data show a shift in flow away from endocardium in Sp and toward endocardium in Sb suggesting different perfusion patterns. We conclude that regional, rather than global, subendocardial ischemia occurred in Sp dogs.