Real-time Myocardial Contrast Echocardiography reveals Microvessel Recruitment Soon after Coronary Occlusion

Background and Aim: Collateral flow at the micro-vessel level is important to salvage the myocardium after acute coronary obstruction, although larger collateral vessels are observed by coronary angiography. The aim of this study was to elucidate the presence of micro-collateral channel by real-time myocardial contrast echocardiography (MCE). Methods: Short axis view of the left ventricle was recorded using real -time imaging by Sequoia 512 during infusion of 0.1 ml/min of Optison( in 17 open-chest dogs. All bubbles were destroyed by one-second exposur e of high acoustic power just after LCx occlusion. The territory of LCx was divided into 3 areas (1 Core and 2 Border zones), and the systolic wall thickening (s-WT) and contrast echo video intensity (VI) were evaluated in each zone just before and 20 seconds after LCx occlusion. It was defined that the collateral channels were good when the mean VI of core and border zones were over 20/256 gray level despite complete occlusion of LCx. The flow volume of left anterior descending coronary artery (LAD) was measured by an ultrasonic flowmeter. Results: It was determined that 7 cases had good collateral channels and other 10 cases had not. The area of risk was gradually but definitely opacified in Good group. Total VI of 3zones was significantly higher in Good group than those in Poor group (69.8+40.3 vs 12.3+6.4, p<0.001). Even in Good group, the VI of core zone was significantly lower than that of border zone (11.3+11.2 vs. 35.3+17.4, p<0.001). Mean s-WT of 3 zones was significantly higher in Good group than those in Poor group (18.8+8.6 vs. 5.5+3.3, p<0.001). S-WT correlated well with VI in all zones of all cases (r=0.916, p<0.001). The LAD flow volume increased 26.2+13.6% during LCx occlusion in Good group, while 10.5+5.3 % in Poor group. Conclusion: It is revealed that real-time MCE demonstrates the recruitment of a fine and thin collateral channel appearing soon after coronary occlusion. This finding has not been elucidated so far by other modalities. Real-time MCE can elucidate the mechanism of myocardial salvage after acute coronary obstruction in both clinical and experimental aspect.