Shape of the human cardiac ventricles

Previous studies suggest that intramural myocardial architecture is arranged to maximize the efficiency of contraction. To examine the topography of the cardiac ventricles for a possible similar functional economy, measurements were made of the heart weight and ventricular wall curvature, thickness, chamber volumes and axial diameters in 80 hearts, with and without ventricular dilatation or hypertrophy, or both, that had normal coronary arteries and no myocardial lesions. Hearts in various positions of contraction were studied after postmortem arteriography and fixation in distension. Indexes of curvature-thickness were calculated from the measurements using the Laplace relation. The ventricles consist of three mutually intersecting curved partitions, right and left free walls and interventricular septum, which are segments of prolate spheroids. The septum usually curves so as to function as part of the left ventricle but is thinner and flatter than the free wall. Indexes of curvature-thickness showed that in the distended position ventricles are more globular and thin-walled; in the contracted position they are more cylindrical and thicker. The left ventricular free wall index showed greater change between distension and contraction than the other components. The results suggest that ventricular configuration is a compromise between a spherical shape that would need the least energy for diastolic ventricular filling and a tubular shape that would permit maximal conversion of systolic myocardial muscle cell tension into cavitary pressure increase. Ventricular topography probably develops as that geometry that requires the minimal energy expenditure in the overall economy of the circulation. Clinical determination of curvature-thickness indexes, similar to the postmortem indexes studied here, may find practical implementation in the assessment of cardiac diseases with two dimensional echocardiography and radionuclide imaging.