Noninvasive Analysis of Myocardial Function Using High-Resolution Doppler Tissue Echocardiography in Rats

Abstract

The widespread use of rodent models of cardiovascular disease has demanded improved methods of assessing myocardial function. Recently, invasive measurement of cardiac function using conductance catheterization has become available for assessing ventricular performance in small animals. 1-3 However, although pressure-volume loop analysis has become the gold standard, it is impractical for longitudinal assessment of disease or interventions. The ideal method under these circumstances would be noninvasive, an accurate index of contractile function, resistant to the influence of load, and reproducibly measurable in small animals. Doppler tissue echocardiography (DTE) is a new modality that has been widely used to assess cardiac function noninvasively. 4,5 Many indices of systolic function have been described but, as might be expected, ejection-phase indices have been shown to be load dependent. This limits their applicability to the assessment of intrinsic myocardial contractility. We have recently demonstrated that myocardial isovolumic acceleration (IVA), derived by DTE, is a relatively load-independent index of systolic ventricular function that is also capable of describing the force-frequency relationships in both the right ventricle and left ventricle (LV) in porcine models and human beings. 6,7 DTE has previously been used to assess cardiac function in rodent models. For example, myocardial systolic and diastolic velocity gradients were shown to be abnormal in a rat model of myocardial hypertrophy. 8 However, interpretation of such data obtained with conventional probes, which are limited in terms of both spatial and temporal resolution, is difficult. Furthermore, as in studies of larger animals and human beings, interpretation of noninvasively acquired data can only be complete when the load dependency of the index is understood. To our knowledge, there are no systematically obtained data regarding the load dependency of systolic indices of function measured by DTE. This study assesses the use of DTE indices in small rodents. Using a high-resolution probe, we investigated IVA, isovolumic velocity (IVV), and systolic wall velocity (SW) of the LV myocardium together with simultaneous conductance catheter recording of pressure and volume. We examined contractile function to determine the influence of alterations in preload and afterload, and measured the response of these indices to inotropic change.