Assessment of nonuniformity of transmural myocardial velocities by color-coded tissue Doppler imaging - Characterization of normal, ischemic, and stunned myocardium

Background-Transmural myocardial contractile performance is nonuniform acro ss the different layers of the left ventricular wall. We evaluated the accu racy of color M-mode tissue Doppler imaging (TBI) to assess the transmural distribution of myocardial velocities and to quantify the severity of dysfu nction induced by acute ischemia and reperfusion in the inner and outer myo cardial layers. Methods and Results-Thirteen open-chest dogs underwent 15 minutes of left a nterior descending coronary artery occlusion followed by 120 minutes of rep erfusion. hi-mode TDI was obtained from an epicardial short-axis view. Syst olic velocities were calculated within endocardium and epicardium of the an terior and posterior walls. Regional myocardial blood flow was assessed by radioactive microspheres. Segment shortening was measured by sonomicrometry in endocardium and epicardium of both the anterior and posterior walls. At baseline, endocardial velocities were higher than epicardial velocities, r esulting in an inner/outer myocardial velocity gradient. Ischemia caused a significant and comparable reduction in endocardial and epicardial systolic velocities in the anterior wall with the disappearance of the velocity gra dient. Systolic velocities significantly correlated with segment shortening in both endocardium and epicardium during ischemia and reperfusion. In the first minutes after reflow, endocardial velocities showed a greater improv ement than epicardial velocities, and the velocity gradient resumed althoug h to a limited extent, indicative of stunning. Conclusions-TDI is an accurate method to assess the nonuniformity of transm ural velocities and may be a premising new tool for quantifying ischemia-in duced regional myocardial dysfunction.