Effect of Direct Cardiac Compression on Left Ventricular Axial Dynamics in Sheep

The HeartPatch direct cardiac compression device consists of two separate, nonsurround patches placed on the left and right ventricular free walls. Although the device has been shown to effectively restore circulatory parameters in acute heart failure sheep, the impact of device inflation on left ventricular geometry is yet to be elucidated. This study used sonomicrometer crystal transducers to examine three orthogonal left ventricular dimensions under various cardiac states and assessed the feasibility of determining stroke volume from these dimensions. Seven sheep (weight, 51 ± 5 kg) were implanted with six sonomicrometer crystals, and a heart patch was placed on each of the ventricles. The crystals were positioned to measure anterior-posterior, septal-lateral, and apex-base (long-axis) dimensions. Sheep were studied under both awake and anesthetized conditions. Septal-lateral shortening was increased with direct cardiac compression assist, whereas anterior-posterior and long-axis dimensions were either unchanged (awake) or decreased (anesthetized). Estimation of stroke volume, using the ellipsoid volume model, correlated well with stroke volume measured from an aortic flow probe; however, absolute stroke volumes were lacking in agreement.