Functional assessment of bioprosthetic mitral valves by cardiovascular magnetic resonance: An in vitro validation and comparison to Doppler echocardiography.

BACKGROUND: A comprehensive non-invasive evaluation of bioprosthetic mitral valve (BMV) function can be challenging. We describe a novel method to assess BMV effective orifice area (EOA) based on phase contrast (PC) cardiovascular magnetic resonance (CMR) data. We compare the performance of this new method to Doppler and in vitro reference standards. METHODS: Four sizes of normal BMVs (27, 29, 31, 33 mm) and 4 stenotic BMVs (27 mm and 29 mm, with mild or severe leaflet obstruction) were evaluated using a CMR- compatible flow loop. BMVs were evaluated with PC-CMR and Doppler methods under flow conditions of; 70 mL, 90 mL and 110 mL/beat (n = 24). PC-EOA was calculated as PC-CMR flow volume divided by the PC- time velocity integral (TVI). RESULTS: PC-CMR measurements of the diastolic peak velocity and TVI correlated strongly with Doppler values (r = 0.99, P < 0.001 and r = 0.99, P < 0.001, respectively). Across all conditions tested, the Doppler and PC-CMR measurement of EOA (1.4 ± 0.5 vs 1.5 ± 0.7 cm2, respectively) correlated highly (r = 0.99, P < 0.001), with a minimum bias of 0.13 cm2, and narrow limits of agreement (- 0.2 to 0.5 cm2). CONCLUSION: We describe a novel method to assess BMV function based on PC measures of transvalvular flow volume and velocity integration. PC-CMR methods can be used to accurately measure EOA for both normal and stenotic BMV's and may provide an important new parameter of BMV function when Doppler methods are unobtainable or unreliable.

Functional Assessment of Bioprosthetic Aortic Valves by CMR.

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.

Comparative Assessment of Mitral Regurgitation Severity by Transthoracic Echocardiography and Cardiac Magnetic Resonance Using an Integrative and Quantitative Approach.

Although transthoracic echocardiography (TTE) and cardiac magnetic resonance (CMR) are validated in quantitation of mitral regurgitation (MR), discrepancies may occur. This study assesses the agreement between TTE and CMR in MR and evaluates characteristics and clinical outcome of patients with discrepancy. From our institutional database, 70 subjects with MR underwent both TTE and CMR within 30 days (median 3 days). MR was evaluated semiquantitatively (n = 70) using a 4-grade scale and quantitatively (n = 60) with calculation of regurgitant volume (RVol) and regurgitant fraction (RF). Of the 70 subjects, qualitative assessment by TTE yielded 30 subjects with mild MR, 17 moderate, and 23 moderately severe or severe MR. Exact concordance in MR grade was seen in 50% and increased to 91% when considering concordance within one grade of severity (κ = 0.44). A modest correlation was observed for RVol and RF between both methods (r = 0.59 and 0.54, respectively, p <0.0001). Ten patients had a significant discrepancy in quantitative MR (difference in RF >20%); the frequency of secondary MR was higher (100% vs 46%; p = 0.003) in patients with discrepancy. Although interobserver variability in RF was higher with TTE compared with CMR (-5.5 ± 15% vs 0.1 ± 7.3%), patients with discrepancy were equally distributed by severity and clinical outcome without an overestimation by either method. In conclusion, there is a modest agreement between TTE and CMR in assessing MR severity. In patients with discrepancy, there is a higher prevalence of functional MR, without a consistent overestimation of MR severity by either method.