On the characterization of left ventricular function with acoustic radiation force impulse imaging

Extensive research has been dedicated to investigating the assessment of left ventricular (LV) function via myocardial elasticity. Previous research has demonstrated acoustic radiation force impulse (ARFI) imaging to be capable of visualizing variations in myocardial stiffness through the entire cardiac cycle. Accordingly, ARFI imaging across multiple heartbeats may be able to provide additional insight into the beat-to-beat changes in myocardial performance and left ventricular (LV) function. Single-line M-mode ARFI images of the LV free wall of a ovine subject were taken before and after individually varying four determinants of left ventricular function: heart rate, preload, afterload, and contractility. The heart was imaged under an open-chest preparation, with the transducer placed directly on the LV free wall. In each pair of image acquisitions, the ARFI imaging-determined end-systolic stiffness, end-diastolic stiffness and rate of systolic stiffening were compared. With ARFI imaging, the end-systolic stiffness only to vary with a change in contractility. End-diastolic stiffnesses were observed to increase with increased heart rate, and decreased with decreased preload and increased afterload. The rates of systolic stiffening were seen to decrease with increasing heart rate, decreasing preload, and increasing afterload. These results can generally be corroborated by similar PV analysis-based research and the Frank-Starling law of the heart.