Validation of echocardiographic and Doppler indexes of left ventricular relaxation in adult hypertensive and normotensive rats

This study was performed to validate echocardiographic and Doppler techniques for the assessment of left ventricular (LV) diastolic function in spontaneously hypertensive rats (SHR) and normotensive Wistar rats. In 11 Wistar rats and 20 SHR, we compared 51 sets of invasive and Doppler LV diastolic indexes. Noninvasive indexes of LV relaxation were related to the minimal rate of pressure decline (-dP/dtmin), particularly isovolumic relaxation time (IVRT), the Tei index, the early velocity of the mitral annulus (Em) using Doppler tissue imaging, and early mitral flow propagation velocity using M-mode color (r = 0.28 - 0.56 and P < 0.05 - 0.0001). When the role of systolic load was considered, the correlation between Doppler indexes of LV diastolic function and relaxation rate [(-dP/dt(min))/LV systolic pressure] improved (r = 0.48 - 0.86 and P = 0.004 - 0.0001, respectively). Similarly, Doppler indexes of LV diastolic function and the time constant of isovolumic LV relaxation (tau) correlated well (r = 0.50 - 0.84 and P = 0.0002 - 0.0001, respectively). In addition, eight SHR and eight Wistar rats were compared; their LV end-diastolic diameters were similar, whereas the SHR LV mass was greater. Furthermore, IVRT and Tei index were significantly higher and Em was lower in SHR. Moreover, tau was higher in SHR, demonstrating impaired LV relaxation. In conclusion, LV relaxation can be assessed reliably using echocardiographic and Doppler techniques, and, using these indexes, impaired relaxation was demonstrated in SHR.