Total heart volume variation throughout the cardiac cycle in humans.

Variations in total heart volume (atria plus ventricles) during a cardiac cycle affect efficiency of cardiac pumping. The goals of this study were to confirm the presence, extent, and contributors of total heart volume variation during the cardiac cycle in healthy volunteers with the use of MRI. Eight healthy volunteers were examined by MRI at rest. Changes in total cardiac volume throughout the cardiac cycle were calculated using the following methods: 1) planimetry derived from gradient-echo cine images and 2) flow-sensitive sequences to quantify flow in all vessels leading to and from the heart. The maximum total heart volume diminished during systole by 8.2 +/- 0.8% (SEM, range 4.8-10.6%) measured by method 1 and 8.8 +/- 1.0% (SEM, range 5.6-11.8%) by method 2 with good agreement between the methods [difference according to Bland-Altman analysis -0.6% +/- 1.0% (SD), intraclass correlation coefficient = 0.999]. This decrease in volume is predominantly explained by variation at the midcardiac level at the widest diameter of the heart with a left-sided predominance. In the short axis of the heart, the change of slice volume was proportional to the end-diastolic slice volume. The present study has confirmed the presence of total heart volume variation that predominantly occurs in the region of atrioventricular plane movement and on the left side. The total heart volume variation may relate to the efficiency of energy use by the heart to minimize displacement of surrounding tissue while accounting for the energy required to draw blood into the atria during ventricular systole.