Assessment of mitral bioprostheses using cardiovascular magnetic resonance

Abstract

Background: The orifice area of mitral bioprostheses provides important information regarding their hemodynamic performance. It is usually calculated by transthoracic echocardiography (TTE), however, accurate and reproducible determination may be challenging. Cardiovascular magnetic resonance (CMR) has been proven as an accurate alternative for assessing aortic bioprostheses. However, whether CMR can be similarly applied for bioprostheses in the mitral position, particularly in the presence of frequently coincident arrhythmias, is unclear. The aim of the study is to test the feasibility of CMR to evaluate the orifice area of mitral bioprostheses.

Methods: CMR planimetry was performed in 18 consecutive patients with mitral bioprostheses (n = 13 Hancock(R), n = 4 Labcore(R), n = 1 Perimount(R); mean time since implantation 4.5 +/- 3.9 years) in an imaging plane perpendicular to the transprosthetic flow using steady-state free-precession cine imaging under breath-hold conditions on a 1.5T MR system. CMR results were compared with pressure half-time derived orifice areas obtained by TTE.

Results: Six subjects were in sinus rhythm, 11 in atrial fibrillation, and 1 exhibited frequent ventricular extrasystoles. CMR image quality was rated as good in 10, moderate in 6, and significantly impaired in 2 subjects. In one prosthetic type (Perimount(R)), strong stent artifacts occurred. Orifice areas by CMR (mean 2.1 +/- 0.3 cm2) and TTE (mean 2.1 +/- 0.3 cm2) correlated significantly (r = 0.94; p < 0.001). Bland-Altman analysis showed a 95% confidence interval from -0.16 to 0.28 cm2 (mean difference 0.06 +/- 0.11 cm2; range -0.1 to 0.3 cm2). Intra- and inter-observer variabilities of CMR planimetry were 4.5 +/- 2.9% and 7.9 +/- 5.2%.

Conclusions: The assessment of mitral bioprostheses using CMR is feasible even in those with arrhythmias, providing orifice areas with close agreement to echocardiography and low observer dependency. Larger samples with a greater variety of prosthetic types and more cases of prosthetic dysfunction are required to confirm these preliminary results.

Figure 1

Slice positioning for prosthetic orifice planimetry. A) and B) 3- and 4-chamber-view showing the mitral bioprosthesis. Planning the next slice in the 4-chamber view along the transprosthetic jet (white line). C) Again planning the next plane centrally through the transprosthetic jet. D) Positioning a stack of slices perpendicular to the jet covering the prosthesis during cardiac motion. E) and F) Cross section of the mitral bioprosthesis in systole and diastole. G) Manual contouring of the largest diastolic orifice area.

Figure 2

Mitral bioprostheses imaged by CMR. A) and B) Hancock^® #29, implanted 1998, imaged during sinus rhythm. C) and D) Labcore^® #29, implanted 2005, imaged during atrial fibrillation. E) and F) Perimount^® #31, implanted 2001, imaged during atrial fibrillation, with strong artifacts caused by the stent.

Figure 3

Comparison of CMR and TTE. Scattergram (left) and Bland-Altman plot (right) comparing the prosthetic orifice areas obtained by CMR and TTE. (Middle dotted line indicates the mean difference; outer dotted lines indicate the limits of 2 standard deviations of the difference).

Figure 4

Comparison of SSFP and FGRE. Hancock^® #31, implanted 2008, imaged during sinus rhythm by SSFP (A and B) and FGRE (C and D).