Aortic Regurgitation Quantitation in Continuous-Flow LVAD
Is there an echo/Doppler technique to measure aortic regurgitant (AR) flow throughout the entire cardiac cycle, more accurately describing AR in patients with a continuous-flow left ventricular assist device (LVAD)?
In a prospective study, LVAD patients with varying degrees of AR (n = 20) underwent simultaneous right heart catheterization (RHC) and transthoracic echocardiogram (TTE). Regurgitant fraction across the aortic valve was calculated by subtracting the cardiac output (obtained using the Fick method) from the total systemic flow (measured using the sum of the product of the velocity time integral and cross-sectional area of the LVAD outflow cannula and aortic valve, respectively). The regurgitant fractions were then compared to: a) traditional TTE grading parameters, and b) new TTE parameters unique to LVAD physiology: the diastolic flow acceleration and the systolic-to-diastolic velocity ratio of the LVAD outflow cannula.
Patients without evidence of AR had a regurgitant fraction approaching zero (2.4 ± 4.6%). Patients with trace and mild AR had a regurgitant fraction of 31.0 ± 5.4%, while patients with moderate or severe AR had regurgitant fraction of 45.8 ± 3.6%. Regurgitant fraction correlated better with pulmonary capillary wedge pressure (PCWP) than with vena contracta width (R = 0.73 vs. 0.56). The new TTE parameters (systolic-to-diastolic ratio and diastolic acceleration) highly correlated with regurgitant fraction (R = 0.91 and 0.94, respectively) and more strongly correlated with PCWP than with vena contracta (R = 0.82 and 0.65 vs. 0.56).
Regurgitant fraction measured by simultaneous RHC and TTE better correlates with clinical filling pressures than with traditional TTE parameters, and may identify significant AR that might be underestimated using conventional measures. Novel TTE parameters unique to continuous-flow LVAD physiology better correlate with regurgitant fraction and filling pressures than do conventional TTE measurements of AR.
AR (which spans systolic as well as diastole) is a common clinical problem following continuous-flow LVAD implantation. Current echocardiographic evaluation of AR does not take into account the unique flow properties present in patients with a continuous-flow LVAD. This study suggests that conventional echo/Doppler measures of AR do not correlate well in this population with what is probably the true regurgitant load, but that echo/Doppler assessment of diastolic flow acceleration and the systolic-to-diastolic velocity ratio of the LVAD outflow cannula can be used to better describe AR in patients with a continuous-flow LVAD.
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