Towards comprehensive assessment of mitral regurgitation using cardiovascular magnetic resonance

Abstract

Cardiovascular magnetic resonance (CMR) is increasingly used to assess patients with mitral regurgitation. Its advantages include quantitative determination of ventricular volumes and function and the mitral regurgitant fraction, and in ischemic mitral regurgitation, regional myocardial function and viability. In addition to these, identification of leaflet prolapse or restriction is necessary when valve repair is contemplated. We describe a systematic approach to the evaluation of mitral regurgitation using CMR which we have used in 149 patients with varying etiologies and severity of regurgitation over a 15 month period. Following standard ventricular cine acquisitions, including 2, 3 and 4 chamber long axis views and a short axis stack for biventricular function, we image movements of all parts of the mitral leaflets using a contiguous stack of oblique long axis cines aligned orthogonal to the central part of the line of coaptation. The 8-10 slices in the stack, orientated approximately parallel to a 3-chamber view, are acquired sequentially from the superior (antero-lateral) mitral commissure to the inferior (postero-medial) commissure, visualising each apposing pair of anterior and posterior leaflet scallops in turn (A1-P1, A2-P2 and A3-P3). We use balanced steady state free precession imaging at 1.5 Tesla, slice thickness 5 mm, with no inter-slice gaps. Where the para-commissural coaptation lines curve relative to the central region, two further oblique cines are acquired orthogonal to the line of coaptation adjacent to each commissure. To quantify mitral regurgitation, we use phase contrast velocity mapping to measure aortic outflow, subtracting this from the left ventricular stroke volume to calculate the mitral regurgitant volume which, when divided by the left ventricular stroke volume, gives the mitral regurgitant fraction. In patients with ischemic mitral regurgitation, we further assess regional left ventricular function and, with late gadolinium enhancement, myocardial viability. Comprehensive assessment of mitral regurgitation using CMR is feasible and enables determination of mitral regurgitation severity, associated leaflet prolapse or restriction, ventricular function and viability in a single examination and is now routinely performed at our centre. The mitral valve stack of images is particularly useful and easy to acquire.

Figure 1

Anatomy of the mitral valve. CMR short axis view of the mitral valve from a basal short axis slice showing its two leaflets (anterior and posterior) and the three scallops of each leaflet (A1, A2 and A3 in the anterior leaflet, P1, P2 and P3 in the posterior leaflet). The mitral valve is viewed from the LV looking towards the left atrium.

Figure 2

Imaging a thin structure or boundary using a relatively thick slice. Because the voxels that contribute to a CMR cine image are elongated, their length being the thickness of the slice, orthogonal orientation of the slice relative to a thin structure or boundary depicts the structure more clearly than oblique orientation. This principle is fundamental to the strategies described in this paper for the imaging of the mitral leaflets and associated regurgitant jets.

Figure 3

Slices taken across the mitral valve. 5 mm thick slices are taken starting from the superior (antero-lateral) commissure (A1-P1) and moving towards the inferior (postero-medial) commissure (A3-P3) at 5 mm intervals. The orientation of the slice is parallel to the LVOT slice.

Figure 4

Additional imaging slices at each end of the mitral valve. A further pair of slices orthogonal to the coaptation plane of the valve leaflets is taken at the commissures at each end of the mitral valve (A1-P1 and A3-P3) to better visualise these scallops.

Figure 5

Images obtained of each scallop of the mitral valve. Each scallop of both mitral valve leaflets is clearly visualised: (a) A1-P1, (b) A2-P2, (c) A3-P3. Moderate centrally directed mitral regurgitation is seen most marked at (b) A2-P2 due to leaflet restriction following myocardial infarction.

Figure 6

Prolapse of P2 causing mitral regurgitation. (a) A1-P1, (b) A2-P2, (c) A3-P3. Arrowhead shows the posterior leaflet. This can be seen to be prolapsed at (b) P2. The yellow line shows the mitral annular plane. The arrows show the eccentric jet of mitral regurgitation which results from failure of coaptation of A2-P2 and is anteriorly directed along the wall of the left atrium. The white arrow points to a central bright jet core in the A2-P2 bSSFP image, with a dark streak of signal loss beyond (grey arrow). This is in accord with relatively severe regurgitation.