Abstract 2347: Quantification of Transmural Gradient of Myocardial Blood Flow with Real-time Myocardial Contrast Echocardiography and Dipyridamole Stress Test
Although it has been long recognized that transmural redistribution of myocardial blood flow (MBF) is the earliest sign of myocardial ischemia, an accurate approach to the non-invasive assessment of the transmural gradient of MBF is still lacking. In the present study, we assessed the hypothesis that real-time myocardial contrast echocardiography (MCE) combined with dipyridamole stress test enables quantification of the transmural gradient of MBF during graded coronary stenoses. Real-time MCE was performed in 14 open-chest dogs at 7 states: baseline, maximal hyperemia induced by continuous infusion of dipyridamole, 50%, 75% and 90% reduction of the hyperemic flow, reperfusion and total occlusion of the left anterior descending coronary artery (LAD). MCE perfusion parameters were obtained from the subendocardial (A-endo, β-endo and A×β-endo) and subepicardial (A-epi, β-epi and A×β-epi) layers, and the transmural gradients of these parameters (A-EER, β-EER and A×β-EER) and systolic wall thickening (SWT) were calculated. The sensitivity and specificity of each parameter for predicting mild myocardial ischemia were derived using receiver-operating characteristics (ROC) curve analysis. The results showed that no transmural gradients of A, β and A×β were found at baseline, during maximal hyperemia and 50% reduction of the hyperemic flow. β-endo, A×β-endo, β-EER and A×β-EER decreased significantly when the maximal hyperemic flow was reduced by 75% or more (P < 0.05 ~ 0.01). In contrast, SWT remained unchanged until the maximal hyperemic flow was reduced by 90% or more. After reperfusion, all MCE measurements recovered to the hyperemic level while SWT was only partially restored. Among all parameters measured, β-EER had the highest, while SWT had the lowest, sensitivity and specificity in predicting 75% reduction of the hyperemic flow. In conclusion, real-time MCE combined with dipyridamole stress allows quantification of the transmural gradient of MBF. β-EER is more sensitive than SWT and other MCE parameters in detecting mild myocardial ischemia.