Myocardial contrast echocardiography and the transmural distribution of flow: A critical appraisal during myocardial ischemia not associated with infarction

AbstractObjectives. This study was undertaken to determine whether myocardial contrast echocardiography can be used to estimate the transmural distribution of flow.Background. Myocardial contrast echocardiography has been shown to reliably measure average transmural blood flow during myocardial ischemia. However, there is controversy regarding its ability to determine the transmural distribution of flow.Methods. The transmural distribution of flow was measured in 21 open chest anesthetized dogs with use of radiolabeled microspheres and sonicated albumin microbubbles (mean size 4.5 μm). In the 11 Group I dogs, myocardial contrast echocardiography was performed at baseline and during left anterior descending artery stenosis. In five of these dogs, it was also performed during left circumflex artery stenosis. In these dogs large (mean 12 μm) hand-agitated bubbles were also used. In the five Group II dogs, myocardial contrast echocardiography was performed before and 45 s after intracoronary injection of 6 mg of papaverine in the presence of a critical left circumflex artery stenosis. The five Group III dogs were studied during cardiopulmonary bypass at baseline and during left anterior descending artery stenosis. Off-line image analysis of the echocardiographic images was performed and timeintensity curves obtained from thess images were correlated with radiolabeled microsphere-derived flows.Results. The ratios of the parameters derived from the endocardium and epicardium during myocardial contrast echocardiography were found to correlate poorly (ranging from R2= 0 to R2= 0.35) with radiolabeled microsphere-derived endocardial/ epicardial flow ratios over a wide range of flow ratios (0.01 to 2.58). These results were not influenced either by the location of the regions of interest (left anterior descending vs. left circumflex artery bed) or by the size of the bubbles (4.5 vs. 12 μm).Conclusions. Myocardial contrast echocardiography cannot be used to assess the transmural distribution of flow during myocardial ischemia not associated with infarction

Assessment of regional myocardial blood flow with myocardial contrast two-dimensional echocardiography

AbstractIt was hypothesized that regional myocardial blood flow could be measured using myocardial contrast echocardiography. Accordingly, arterial blood was perfused into the coronary circulation in 16 dogs. In Group 1 dogs (n = 8), blood flow to the cannulated left circumflex artery was controlled with use of a roller pump, whereas in Group 2 dogs (n = 8) blood flow to the left anterior descending coronary artery was controlled by a hydraulic occluder placed around it. Sonicated microbubbles (mean size 4 μm) were used as the contrast agent. In Group 1 dogs the microbubbles were injected subselectively into the left circumflex artery, whereas in Group 2 dogs they were injected selectively into the left main coronary artery and two-dimensional echocardiography images were recorded. Computer-generated time-intensity curves were derived from these images and variables of these curves correlated with transmural blood flow measured with radiolabeled microspheres.A gamma-variate function (y = Ate−∞tbest described the curves, and 1/2 (a variable of curve width) correlated well with transmural blood flow at different flow rates in all Group 1 and Group 2 dogs (mean r = 0.81 and 0.97, respectively). Other variables of the curve width also correlated well with myocardial blood flow, but peak intensity had a poor correlation with myocardial blood flow in both groups of dogs (r = 0.39 and r = 0.63, respectively). When data from all dogs were pooled, Group 1 dogs still showed good correlation between variables of curve width and myocardial blood flow (r = 0.81); Group 2 dogs did not (r = 0.45). The difference between the two sets of dogs was related to the site of contrast agent injection.It is concluded that measurement of the transit time of microbubbles through the myocardium with two-dimensional echocardiography accurately reflects regional myocardial blood flow. Although injection of contrast agent selectively into the left main coronary artery only allows measurement of relative flow, it may be feasible to measure absolute flow by injecting contrast agent subselectively into a coronary artery. Myocardial contrast echocardiography may, therefore, offer the unique opportunity of simultaneously assessing regional myocardial perfusion and function in vivo