Parametric pressure-volume analysis and acoustic radiation force impulse imaging of left ventricular function

Extensive research has been devoted to the quantification of left ventricular (LV) function via an elasticity metric known as elastance. Similar to a stress-strain relation, yielding stiffness, myocardial elastance is measured from the pressure-volume (PV) relation within the left ventricle. ARFI imaging has been shown to be capable of measuring myocardial stiffness changes through the cardiac cycle. As a result, a parametric analysis of ARFI imaging and the PV relation could provide additional insight into LV function and performance. The heart of a canine subject was imaged under an open chest preparation. Co-registered B-mode and M-mode ARFI imaging sequences were acquired while simultaneously recording LV pressures, and the global electrocardiogram (ECG). LV pressures were measured with a Millar Instruments pressure catheter, and LV volumes were extrapolated via semi-automatic segmentation of LV chambers within the acquired two-dimensional B-mode images. The resultant temporally registered plots were examined and compared. A parametric analysis between temporally registered LV pressure, LV volume, and ARFI-induced displacement curves related myocardial stiffness to the four phases of the cardiac cycle. The parametric plots of these data indicated that the changes in myocardial stiffness generally followed the changes in LV pressures, as ARFI-induced displacements fell during isovolumic contraction and rose during isovolumic relaxation. However, the plots also showed that ARFI-induced displacements continued to rise through all of filling, while LV pressures remained relatively constant.