Detection of Viable Myocardium by Transvenous Myocardial Contrast Echocardiography Using Harmonic Power Doppler: Canine Model of Acute Coronary Occlusion and Reperfusion

Abstract

To assess whether myocardial contrast echocardiography (MCE) using harmonic power Doppler (HPD) in conjunction with the transvenous contrast agent SHU 563A would be useful in detecting stunned but viable myocardium. Acute coronary occlusion (2 to 3 h) followed by 1 h of reperfusion was created in 10 dogs in an open-chest model. Continuous harmonic B-mode for wall motion analysis and ECG triggered HPD for assessment of myocardial perfusion was employed during coronary occlusion and after reperfusion. Postmortem 2,3,5-triphenyltetrazolium chloride (TTC) staining was performed to verify infarction. Extent of wall motion abnormality (WMA), perfusion defect size, and anatomic infarct size (myocardial infarction [MI]) were analyzed in a 5-segment model. All 10 dogs showed WMA in 23 of 50 segments during coronary occlusion. In eight dogs, HPD detected perfusion defects in 18 of 50 segments. The concordance rate between WMA and perfusion defect was 86%. Mean linearized power (MLP) in segments with WMA was significantly lower compared to normal segments (60.7 +/- 38.9 vs 110.5 +/- 108.8, p < 0.05). After reperfusion, the extent of WMA was larger than the area of perfusion defect (percentage of left ventricular slice area): 30 +/- 13% vs 9 +/- 8%, p < 0.01. Eventual infarct size was 6 +/- 7%. WMAs were seen in 18 of 50 segments. TTC confirmed MI in 7 of 18 segments. MLP in segments with WMA but no MI was significantly higher compared to segments with WMA and MI (84.5 +/- 67.3 vs 13.2 +/- 9.6, p < 0.01). Thus, the extent of WMA after reperfusion was greater than the size of perfusion defect and eventual MI, indicating the presence of stunned but viable myocardium. MCE using HPD and the contrast agent SHU 563A can demonstrate the efficacy of reperfusion, identify necrotic regions, and aid in the recognition of stunned but viable myocardium. This approach could be useful clinically in patients with acute MI undergoing reperfusion therapy.