Correlation of myocardial echo contrast disappearance rate (“Washout”) and severity of experimental coronary stenosis

The relation between experimental coronary stenosis and myocardial contrast echo disappearance rate (“washout”) was investigated in anesthetized closed chest dogs. Of 13 dogs, 8 had serial contrast echographic studies with two successive degrees of coronary stenosis (50 and 70%) produced by threading stenotic plugs into the proximal left circumflex coronary artery. Studies were repeated with complete coronary occlusion achieved by inflation of an intracoronary balloon immediately proximal to the plugs. Myocardial contrast echograms were recorded in short-axis cross sections of the left ventricle after intracoronary injection of 2 ml hand-agitated sa-line-Renografin solution through a catheter placed in the coronary artery. An echo contrast washout index (t ½) was measured by digital processing computer analysis of successive end-diastolic images obtained by two-dimensional echocardiography during myocardial contrast agent injection. The injection to injection correlation coefficient of these t ½ measurements was satisfactory (r = 0.87, standard error of estimate 4.8 seconds). Involved segment t ½ measurements were found to be significantly altered by intracoronary stenosis and occlusion, ranging from 23 ± 6 seconds (mean ± standard deviation) in the control state, 29 ± 9 and 44 ± 10 seconds for 50 and 70% stenosis, respectively, and 104 ± 35 seconds for total occlusion. It was concluded that myocardial contrast two-dimensional echocardiographic measurement of t ½ appears to be a useful index of the degree of coronary stenosis.