ASSESSMENT OF TRANSMURAL DISTRIBUTION OF MYOCARDIAL PERFUSION WITH CONTRAST ECHOCARDIOGRAPHY

Background-We hypothesized that by using our newly defined method of d estroying microbubbles and measuring their rate of tissue replenishmen t, we could assess the transmural distribution of myocardial perfusion . Methods and Results-We studied 12 dogs before and after creation of left anterior descending coronary artery stenoses both at rest and dur ing hyperemia (n=62 stages). Microbubbles were administered as a const ant infusion, and myocardial contrast echocardiography (MCE) was perfo rmed with the use of different pulsing intervals. The video intensity versus pulsing interval plots derived from each myocardial pixel were fitted to an exponential function: y=A(1-e(beta t)), where A reflects microvascular cross-sectional area (or myocardial blood volume), and b eta reflects mean myocardial microbubble velocity. The product A . bet a represents myocardial blood flow (MBF), Average values for these par ameters were derived from the endocardial and epicardial regions of in terest placed over the left anterior descending coronary artery bed. R adiolabeled microsphere-derived MBF was also measured from the same re gions. There was poor correlation between radiolabeled microsphere-der ived MBF and A-endocardial/epicardial ratios (EER) (r=0.46), The corre lation with beta-EER was better (r=0.69, P<0.01). The best correlation with radiolabeled microsphere-derived MBF-EER was noted with A . beta -EER (r=0.88, P<0.01). Conclusions-The transmural distribution of myoc ardial perfusion can be accurately assessed with MCE with the use of o ur newly described method of tissue replenishment of microbubbles afte r their ultrasound-induced destruction. In the model studied, an uncou pling of the transmural distribution of MBF and myocardial blood volum e was observed during reversal of the MBF-EER.