Regional coronary blood flow in ponies

Regional coronary blood flow was measured by injecting radioactive microspheres (15 mum +/- 5 in diameter) into the left atrium of anesthetized ponies with surgically prepared open thorax before and during occlusion of the coronary arteries. The normal blood flow to the myocardium of the interventricular septum and the left ventricular wall were highest, followed in decreasing order by the right ventricular wall, the interatrial septum, the atrial walls, and the valves. Measurement of transmural blood flow in the normal left ventricle yielded a mean endocardial/epicardial flow ratio of 1.36 in the free wall. The left ventricular flow ratio was 1.33 in the septal wall. The percentage of the left ventricular myocardium made ischemic during occlusion of the right coronary artery or of the left coronary artery (cranial descending and circumflex arteries) was approximately equal. Blood flow to the ischemic areas of the left ventricle after occlusion of coronary arteries ranged from 3.8 to 20.6% of the normal flow. A disproportionate decrease in flow to the endocardial regions of the left ventricle was also observed in ischemic areas (mean inner/outer left ventricular wall flow ratio was 68.89% of the normal flow ratio).