Abstract 19155: Pulsatile Load is a More Important Determinant of Peak Fiber Stress than Valve Area in Aortic Stenosis

Abstract

Background: In aortic stenosis (AS), the valve imparts an additional hemodynamic burden on the LV in proportion to the degree of valve narrowing. Yet the relative contributions of valve stenosis and arterial load on LV fiber stress are unknown. Furthermore, it has recently been shown that end-systolic measurements of wall stress are unrepresentative of the time-resolved wall stress patterns. Yet, time-resolved LV fiber stress has never been assessed in AS. Hypothesis: Arterial load is an important determinant of time-resolved wall stress in AS. Methods: We assessed time-resolved LV geometry (using SSFP cine MRI), aortic flow (using phase-contrast MRI) and central aortic pressure (using carotid tonometry) among 40 patients with AS (16 mild, 20 moderate, and 4 severe AS). Arterial load parameters were determined using pressure-flow analyses, including systemic vascular resistance, characteristic impedance of the aorta (Zc), total arterial compliance (pulse-pressure method, TAC), and the amplitudes of the backward (Pb) and forward (Pf) waves. We computed time-resolved ejection-phase myocardial fiber stress using the Arts method. Results: Peak fiber stress occurred at 94.4 msec into systole and was significantly greater than end-systolic fiber stress (847±265 vs. 361±149 kdynes/cm2, P<0.0001). After adjusting for cardiac output, AVA, and end-diastolic mass and volume, Pb, TAC, and SVR were all associated with peak and end-systolic fiber stress (Table). Interestingly, while AVA was associated with peak stress, it was not associated with end-systolic stress in any model. Conclusion: Peak fiber stress occurs early in systole in AS, demonstrating the importance of time-resolved fiber stress assessments. Our findings demonstrate important contributions from the arterial system to LV fiber stress in AS, including resistive load and various measured of pulsatile arterial load.