Effect of afterload alterations on the functional border zone measured with two-dimensional echocardiography during acute coronary occlusion.

In the setting of acute myocardial infarction, pharmacologic intervention resulting in afterload changes are common but the effect of these changes on regional left ventricular function, and specifically the functional border zone, has not been fully investigated. Accordingly, we studied the effects of afterload manipulation on circumferential flow-function relationships and the functional border zone in 16 open-chest, anesthetized dogs. During left circumflex coronary artery occlusion, eight animals were infused with phenylephrine to increase afterload; eight others received nitroprusside for afterload reduction. Following coronary artery occlusion, subendocardial blood flow and wall thickening decreased in the ischemic zone (p less than 0.001). The circumferential extent of hypoperfusion did not differ when coronary artery occlusion alone was compared to occlusion in combination with phenylephrine or nitroprusside, but in both groups the circumferential extent of the wall thickening abnormality was consistently greater than the extent of hypoperfusion. When blood pressure was decreased by 33%, the extent of the functional border zone did not change relative to that during coronary artery occlusion (22 +/- 11 degrees vs 36 +/- 16 degrees, p = ns). Similarly, when blood pressure was increased by 47%, the extent of the functional border zone did not change (32 +/- 10 degrees vs 37 +/- 10 degrees). Therefore circumferential flow-function relations and the spatial extent of the functional border zone are not altered by changing afterload during acute left circumflex coronary artery occlusion in this model.