Quantification of Transmural Gradient of Blood Flow in Myocardial Ischemia with Real-Time Myocardial Contrast Echocardiography and Dipyridamole Stress Test

Abstract Transmural redistribution of myocardial blood flow (MBF) is the earliest sign of myocardial ischemia. We aimed to evaluate the ability of real-time myocardial contrast echocardiography (MCE) combined with dipyridamole stress to quantify the transmural gradient of MBF during graded coronary stenosis. Real-time MCE was performed in 14 open-chest dogs at seven experimental stages: baseline; hyperemia induced by 6-min infusion of dipyridamole; 50%, 75% and 90% reduction of hyperemic flow after constriction in each stage for 10 min; reperfusion for 10 min; and subtotal occlusion of the left anterior descending coronary artery (LAD) for 90 min. We obtained MCE perfusion parameters from subendocardial (A-endo, β-endo and A × β-endo) and subepicardial (A-epi, β-epi and A × β-epi) layers of the ventricular septum and calculated their transmural gradients (A-EER, β-EER and A × β-EER) and systolic wall thickening (SWT). The sensitivity and specificity of each parameter for predicting 75% reduction of hyperemic flow, which was defined as mild myocardial ischemia, were derived by receiver operating characteristic (ROC) curve analysis. No transmural gradients were found at baseline; during maximal hyperemia and 50% reduction of hyperemic flow. β-endo, A × β-endo, β-EER and A × β-EER decreased significantly when the hyperemic flow was reduced by 75% or more. In contrast, SWT remained unchanged until the hyperemic flow was reduced by 90%. Among all parameters measured, β-EER and A × β-EER had the highest and SWT the lowest sensitivity and specificity in predicting mild myocardial ischemia. In conclusion, real-time MCE combined with dipyridamole stress allows for quantification of the transmural gradient of MBF. β-EER and A × β-EER are more sensitive than SWT and other MCE parameters in detecting mild myocardial ischemia. (E-mail: yaogh@yahoo.com ; yun-zhang@163.com )