End-systolic radius to thickness ratio: An echocardiographic index of regional performance during reversible myocardial ischemia in the conscious dog

Regional myocardial dysfunction induced by ischemia is associated with less thickening and a larger ventricular radius at end-systole. Thus, end-systolic radius to thickness ratio measured by echocardiography may provide an accurate index of regional left ventricular function that is totally independent of cardiac motion. To test this hypothesis, a total of 14 transient (≤10 minutes) coronary artery occlusions (8 left anterior descending, 6 left circumflex) followed by up to 24 hours of reperfusion were performed in six chronically instrumented conscious dogs providing multiple grades of regional ventricular dysfunction. Regional myocardial thickening fraction was determined with epicardial pulsed Doppler probes and served as an independent standard for comparison with simultaneous echocardiographic measurements. End-systolic radius to thickness ratio and radial shortening fraction were derived from the two-dimensional echocardiographic short-axis view along 12 equidistant radii. In the ischemic zone, percent thickening fraction averaged 22 ± 5% during baseline, decreased to -4 ± 4% during occlusion with gradual return to baseline after reperfusion. End-systolic radius to thickness ratio averaged 1.39 ± 0.25 before coronary occlusion and increased to 2.97 ± 0.48 during occlusion with a gradual return to baseline values. A significant correlation was found between Doppler-determined thickening fraction measurements and echocardiographic end-systolic radius to thickness ratio as well as radial shortening fraction for absolute values (r = 0.83 and 0.75, respectively; n = 65) and percent change from baseline (r = -0.86 and 0.78, respectively). Using 95% confidence limits, the sensitivity and specificity of end-systolic radius to thickness ratio for detecting regional thickening abnormalities were 81 and 79%, respectively, and for the radial shortening method were 89 and 71%, respectively. Thus, measurements of end-systolic radius to thickness ratio provide an alternative echocardiographic method for quantitating regional left ventricular function that compares well with an independent standard and, in contrast to existing methods, is not affected by external cardiac motion.