Background: Myocardial opacification during echocardiography has been demonstrated after left (LA) and right (RA) atrial injections of contrast, and microvascular damage with reduced blood flow and impaired flow reserve has been documented in necrotic myocardial tissue. Therefore, we hypothesized that because of its ability to depict capillary perfusion, myocardial contrast echocardiography (MCE) can be used to define risk area during coronary occlusion and infarct size after reperfusion with LA and RA injections of contrast in the presence of pharmacologically induced coronary hyperemia.
Methods and results: Eighteen open-chest anesthetized dogs with 3 to 6 hours of left anterior descending artery occlusion and 15 minutes of reflow were studied in the presence of either dipyridamole (0.56 mg/kg over a period of 4 minutes) or dobutamine (15 micrograms.kg-1.min-1). Technetium autoradiography was performed for risk area assessment; infarct size was measured with triphenyl tetrazolium chloride; and in 11 dogs, myocardial blood flow was measured with radiolabeled microspheres. A close linear relation was noted between the MCE defect size and autoradiographic risk area during coronary occlusion both during LA (y = 0.95x-0.25, r = .97, P < .001) and RA (y = 0.90x+0.98, r = .86, P < .001) injections of contrast. During reperfusion, the contrast defect size on MCE was always less transmural than during occlusion and correlated closely with infarct size during both LA (y = 1.07x-2.37, r = .98, P < .001) and RA (y = 1.02x-0.61, r = .95, P < .001) injections of contrast. In the 11 dogs in whom radiolabeled microsphere-derived blood flow was measured during reperfusion, an inverse relation was noted between infarct size and transmural blood flow (y = -1.12x+121, r = -.95, P = .001), implying that MCE defects after reperfusion indicate necrotic regions with reduced blood flow or impaired microvascular flow reserve. A close linear relation (y = 0.79x-0.001, r = .98, P < .001) was also noted between endocardial/epicardial ratio of background-subtracted peak video intensity on MCE and endocardial/epicardial blood flow ratio in the eight dogs with infarction who underwent this measurement after reperfusion.
Conclusions: MCE performed with LA and RA injections of contrast in the presence of pharmacologically induced coronary hyperemia can be used to determine, in vivo, the risk area during coronary occlusion and infarct size after reperfusion. These results could have important implications in this era of myocardial reperfusion.