New Estimate of Valvuloarterial Impedance in Aortic Valve Stenosis: A Cardiac Magnetic Resonance Study

Purpose: Valvuloarterial impedance (Z(VA)), estimating left ventricle (LV) afterload, has been proposed in transthoracic echocardiography (TTE) as a predictor of mortality in aortic valve stenosis (AVS). However, its calculation differs from arterial characteristic impedance (Z(C)). Our aim was to apply the concept of Z(C) calculation to estimate Z(VA) from MR with carotid tonometry and to evaluate these indices through their associations with symptoms, LV diastolic function and aortic stiffness. Materials and Methods: In 40 patients with AVS (7613 years), Z(VA-TI) derived from velocity time integral and E/Ea were estimated by TTE. Z(VA-INS), based on Z(C) formula, calculated as the instantaneous pressure gradient to peak flow ratio and aortic compliance were estimated by using MRI at 1.5 Tesla. Results: Both Z(VA) estimates were higher in symptomatic than asymptomatic patients (70722 versus 57953 dyne.s/cm(5), P = 0.031 for Z(VA-INS) and 4.35 +/- 0.16 versus 3.33 +/- 0.38 mmHg.m(2)/mL, P = 0.018 for Z(VA-TI)). Although they were both associated with aortic compliance (r = -0.45; P = 0.006 for Z(VA-INS) and r = -0.43; P = 0.008 for Z(VA-TI)) only Z(VA-INS) was associated with E/Ea (r = 0.50; P < 0.001). In multivariate analysis to identify determinants of E/Ea, a model including age, mean blood pressure, LV ejection fraction, LV mass, and aortic valve area was performed (R-2 = 0.41; P < 0.01). When Z(VA-INS) was added to the model, its overall significance was higher R-2 = 0.56 (P < 0.01) and Z(VA-INS) and LV mass were the only significant determinants. Conclusion: Z(VA-INS) was more strongly associated with diastolic dysfunction than usual parameters quantifying AVS severity. This new Z(VA) estimate could improve LV afterload evaluation.