Regional differences in shortening and relaxation characteristics of the left ventricular wall of normal subjects as studied by biplane coronary cineangiograms.

The coordinates of the ramifying points of the left coronary artery were measured using biplane coronary cineangiograms in 19 patients who were later diagnosed as normal. The spatial distances (segment length) between any two of these points were calculated and one cardiac cycle was plotted frame by frame in order to investigate shortening and relaxation characteristics of the segments. In most instances, the segments evidenced shortenings during systole and prolongations during diastole. The extent of shortening, as a percentage of maximum length ranged from 7.8 to 18.0%. The segments measured at the apex started shortening 77 msec sooner than those at the base, in other words, 90.3 +/- 6.2 msec before the R wave peak on the electrocardiograms. This indicates that the initial shortening at the apex contributes to the build up of left ventricular pressure. While at the base, since it begins to shorten after the completion of the build up in left ventricular pressure, it contributes more to the ejection of blood from the left ventricle. On the other hand, there is little systolic shortening at the atrioventricular groove and in some instances there is systolic expansion, suggesting that in comparison to the other portions of the left ventricle it is assigned an entirely different role.