The Role of Index of Valvular-Arterial Impedance and Systemic Arterial Compliance after Aortic Valve Replacement

Abstract

Mechanical valvular obstruction and reduced arterial compliance combine to increase left ventricular afterload in patinets with aortic stenosis (AS). As a result of the recognition that valvular and arterial abnormalities both play important roles in determining the overall impedance to left ventricular ejection in AS, it is now clear that standard methods of quantifying valvular stenosis, which focus entirely on the valve itself do not adequately characterize the severity, predict the onset, progression, and magnitude of symptoms, or identify the incidence of subsequent adverse event. The valvuloarterial impedance (Zva) provides an estimate of the global left ventricle (LV) hemodynamic load that results from the summation of the valvular and vascular loads, and the concept is very useful because it incorporates stenosis severity, volume flow rate, body size, and systemic vascular resistance. Moreover, Zva can easily be calculated using Doppler echocardiography from 3 simple measurements, that is, the systemic arterial compliance (SAC) in the LV outflow tract, the transvalvular mean gradient, and systolic arterial pressure, it is superior to the standard indexes of AS severity in predicting LV dysfunction. Zva is the best-suited and most relevant parameter to clinically quantify this “global or total” increase in LV hemodynamic load. There is few data regarding effects of surgical aortic valve replacement (AVR) on Zva and SAC. In patients with AS undergoing transcatheter aortic valve implantation (TAVI), acute declines in Zva were reported. Reductions in Zva observed 1 month after TAVI also were shown to persist during a 2-year follow-up, suggesting that pISSN 1975-4612/ eISSN 2005-9655 Copyright © 2016 Korean Society of Echocardiography www.kse-jcu.org http://dx.doi.org/10.4250/jcu.2016.24.3.191