Detection of Subendocardial Ischemia in the Left Anterior Descending Coronary Artery Territory With Real-Time Myocardial Contrast Echocardiography During Dobutamine Stress Echocardiography

Abstract

The purpose of this study was to test whether the transmural delineation of myocardial perfusion during dobutamine stress imaging with real-time myocardial contrast echocardiography (RTMCE) might permit visualization of dobutamine-induced subendocardial ischemia. Significant coronary artery disease can be present despite normal transmural wall thickening (WT) responses during dobutamine stress echocardiography (DSE). One potential reason is dobutamine-induced recruitment of epicardial WT in the presence of subendocardial ischemia. Myocardial perfusion and WT were examined with RTMCE during DSE with a continuous infusion of ultrasound contrast in 94 patients with normal resting WT. Fifty-five of the patients had a >50% diameter stenosis in the left anterior descending coronary artery (LAD). The WT was visually assessed by a blinded reviewer at 2 time periods: initially after a high mechanical index impulse before myocardial contrast replenishment (MCR), and again during MCR. Subendocardial %WT was measured during MCR, if a subendocardial perfusion defect was visually evident, whereas transmural WT was quantified on the pre-MCR images. Fifty patients (91%) with LAD stenoses exhibited a myocardial contrast defect at peak stress, with 45 defects being subendocardial. Transmural WT pre-MCR appeared normal in 35 of the 45 patients with subendocardial perfusion defects (78%). However, a subendocardial WT abnormality was apparent during MCR in 18 of these 35 patients, even though transmural WT was not different from the 17 patients with normal subendocardial WT (33 +/- 15% vs. 36 +/- 14%). Quantitative measurements of WT within the subendocardium were significantly less in the patients with visually evident subendocardial WT abnormalities, when compared with those who seemed to have normal WT during MCR (17 +/- 8% vs. 25 +/- 10%, p < 0.01). In patients with significant LAD disease, RTMCE during DSE detects subendocardial ischemia even when transmural WT appears normal. Real-time myocardial contrast echocardiography should be the preferred ultrasound imaging method when using contrast to detect coronary artery disease during DSE.