Functional Assessment of Bioprosthetic Aortic Valves by CMR

Abstract

Objectives: The aim of this study was to evaluate cardiac magnetic resonance (CMR) phase-contrast (PC) measures of a bioprosthetic aortic valve velocity time integral (PC-VTI) to derive the effective orifice area (PC-EOA) and to compare these findings with the clinical standard of Doppler echocardiography.

Background: Bioprosthetic aortic valve function can be assessed with CMR planimetry of the anatomic orifice area and PC measurement of peak transvalvular systolic velocity. However, bioprosthetic valves can create image artifact and data dropout, which makes planimetry measures a challenge for even experienced CMR readers.

Methods: From our institutional database, we identified 38 patients who had undergone 47 paired imaging studies (CMR and Doppler) within 46 days (median 3 days). Transvalvular forward flow volume by CMR was determined by 3 methods: ascending aorta flow, transvalvular flow, and left ventricular stroke volume. PC-EOA was derived as flow divided by PC-VTI, calculated with a semiautomated MATLAB (Mathworks, Natick, Massachusetts) application for integration of the instantaneous peak transvalvular velocity. Doppler EOA was assessed by the continuity method.

Results: PC-EOA by all 3 flow approaches demonstrated a strong correlation with Doppler EOA (r = 0.949, 0.947, and 0.874, respectively; all p < 0.001) and revealed good agreement (bias = 0.03, 0.03, and 0.28 cm(2), respectively). With Doppler-derived EOA as the reference standard, CMR was able to correctly characterize 24 of 26 valves as normal (EOA >1.2 cm(2)), 12 of 14 possibly stenotic valves (0.8 < EOA < 1.2 cm(2)), and 5 of 7 stenotic valves (EOA <0.8 cm(2); k = 0.826).

Conclusions: We describe a new CMR-based method to derive the EOA for bioprosthetic aortic valves. This method compares favorably to traditional Doppler methods and might be an important additional parameter in the evaluation of prosthetic valves by CMR, particularly when Doppler methods are suboptimal or considered discordant with the clinical presentation.

Keywords: Doppler echocardiography; bioprosthetic aortic valve; cardiac magnetic resonance; phase contrast.