Abstract 18391: Cardiac Magnetic Resonance Imaging for the Functional Assessment of Normal Bioprosthetic Mitral Valves: A Comparison Against in vitro Flow Transducer and Doppler Echocardiography Measurements
Introduction: Few studies have evaluated the accuracy of Cardiac Magnetic Resonance (CMR) imaging for the functional assessment of bioprosthetic mitral valves (BMV). This study aimed to compare CMR measurements of flow volume and orifice area against in vitro flow transducer and Doppler Echo measurements.
Methods: A previously described pulsatile, MRI compatible flow loop was used to generate diastolic flow volumes (DFV) across BMVs (sizes 27, 29, and 31 mm) within a “cardiac” imaging chamber. The imaging chamber was placed within a 1.5 Tesla MRI scanner (Siemens) under DFVs of 70, 90 and 110 ml/beat at 70 bpm. Steady state free precession sequences were used to assess BMV morphology and motion. 2D Phase contrast (PC) pulse sequences were used to assess trans-valvular velocity and mean stroke volume. Anatomic orifice area (AOA) and the effective orifice area (PC-EOA) were measured by 2 independent observers. A 1-5MHz ultrasound probe (iE33, Philips) was used to evaluate trans-valvular inflow velocity and Doppler-EOA.
Results: For bioprosthetic valves, PC-CMR techniques accurately measure forward stroke volume across the range of predefined reference flow volumes (N=10; r=0.99, p<0.001, mean difference 3.5±3.4 ml/beat). PC-CMR peak velocity showed good correlation with Doppler derived values (r=0.91, p<0.001, mean difference -14.5±14.1 cm/s). CMR-derived AOA and PC-EOA correlated well with each other (r=0.87, p<0.05, mean difference 0.04±0.1 cm2). However, CMR-derived AOA and PC-EOA correlated poorly with Doppler derived EOA (r=0.6, p=0.0067, mean difference 0.9±0.17 cm2).
Conclusion: PC-CMR is a promising modality for determining DFVs and assessing velocity through competent BMVs directly at the valve itself. This is inherently different than the normal clinical MRI practice of inferring valvular flow volumes from indirect measurements of aortic flow and ventricular dimension changes.This method could prove useful for regurgitant flow measurement.
- © 2013 by American Heart Association, Inc.