Regional ventricular segmental dynamics in normal conscious dogs

Left ventricular (LV) subendocardial segmental behavior was analyzed during the whole cardiac cycle for different loading and inotropic conditions in six conscious dogs that were instrumented with ultrasonic crystals in the basal (B) and apical (A) LV regions, a LV micromanometer, and an aortic cuff occluder. There were large variations of A and B segmental behavior during isovolumic contraction and relaxation. In contrast, a linear relationship between A and B was observed during ejection but segmental shortening was larger during control in A than in B, whether it was expressed as a percentage of systolic shortening (34.6 +/- 1.1 and 25.0 +/- 1.2%, respectively; P less than 0.005), or whether segments were normalized for passive resting length. This linear relationship during ejection with a slope of 1.49 was not significantly modified by alterations of loading conditions or inotropic state. The larger A than B shortening, independent of the normalization procedure, is attributed to the regional stress distribution in the LV. The absence of regional and cycle invariance particularly during isovolumic phases prevents the inference of ventricular volume from a limited number of dimensions.