Difference of the shortening characteristics between left ventricular endocardium and epicardium as measured by radiopaque markers in experimental dogs

: This study was performed to clarify the difference of shortening characteristics between left ventricular epicardium and endocardium. Four to five pairs of radiopaque markers (lead beads, phi 0.3- 0.8 mm) were implanted just beneath the epicardium and endocardium, respectively in eight open-chest dogs. After the pericardium and thorax were closed, biplane cine-roentgenograms were obtained. The spatial distance (segment length) between any two of the markers was calculated using a digitizer-computer-plotter system. Left ventricular wall thickness (Th) was measured as a distance between epicardial and endocardial markers. The maximum left ventricular thickness (Thmax) was 9.4 +/- 3.4 mm (mean +/- SD), the minimum (THmin) 8.4 +/- 3.1 mm, and a percent increase of wall thickness [(Thmax-Thmin)/Thmin] was 12.7 +/- 6.5%. The value of epicardial segment length divided by endocardial segment length as normalized by each length at R wave of ECG was 1.088 +/- 0.071 at the end of systole and 0.979 +/- 0.016 at end diastole, indicating that endocardial segment shortened and distended more than epicardial segment during systole and diastole, respectively. Epicardial segment began to shorten 3 +/- 26 msec earlier and distend 4 +/- 50 msec earlier than endocardial one. This study revealed a small but consistent difference in the amount of shortening and its initiation and termination between the epicardium and endocardium.