Visualization of subendocardial myocardial ischemia with myocardial contrast echocardiography in humans.

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Abstract
Previous studies indicate the degree of myocardial echo contrast enhancement may be related to regional myocardial perfusion. In this study, myocardial contrast echocardiography was used to characterize changes in the transmural myocardial blood flow distribution that were provoked by rapid atrial pacing in 11 patients with one-vessel coronary artery disease. Ten patients without coronary artery disease served as controls. Myocardial contrast echocardiography was performed by intracoronary injection of 2 ml hand-agitated amidotrizoate sodium meglumine (Urografin-76) and by imaging a short-axis view of the left ventricle with two-dimensional echocardiography before and during injection of the contrast agent. The two-dimensional echocardiographic images at end diastole, before and after injection of the contrast agent, were digitized off-line into a 512 x 512 pixel matrix with 256 gray levels/pixel to quantify the degree of the enhancement of the peak gray level after injection. Transmural myocardial blood flow distribution was evaluated by measuring the ratio of the enhanced gray level in the endocardial half (endo) to that in the epicardial half (epi) (endo:epi gray level ratio) in the anteroseptal, posterolateral, and inferior segments before and just after rapid atrial pacing in each patient. In patients without coronary artery disease, there were no differences in the endo:epi gray level ratio between any of the three segments both before and after pacing. Mean values of the three segments were 0.95 +/- 0.08 before pacing and 0.90 +/- 0.13 after pacing, respectively. In contrast, in patients with coronary artery disease, the endo:epi gray level ratio for the segment supplied with stenotic coronary artery decreased after pacing (0.40 +/- 0.21 vs. 0.93 +/- 0.18, p less than 0.01), probably reflecting subendocardial myocardial ischemia, whereas that for the segment supplied with nonstenotic coronary artery remained unchanged (0.88 +/- 0.20 vs. 0.99 +/- 0.23, NS). Thus, changes in transmural myocardial blood flow distribution with rapid pacing, which may be due to transient subendocardial ischemia, are visualized with myocardial contrast echocardiography.

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