Direct Visualization of Regurgitant Orifice by CMR Reveals Differential Asymmetry According to Etiology of Mitral Regurgitation
Can the regurgitant orifice area (ROA) and anatomy of the mitral apparatus in various forms of mitral regurgitation (MR) be characterized using cardiac magnetic resonance imaging (CMR)?
CMR was performed in 74 patients with variable MR severity and variable etiologies. ROA was determined from a combination of long-axis four- and two-chamber views, from which planes parallel to the valvular plane and perpendicular to the regurgitant jet were identified. The ROA was planimetered in systole and a ROA shape index was calculated as the ratio of the length to width of the orifice. Regurgitant volume (RV) and regurgitant fraction (RF) were also calculated. Additional CMR measurements included tenting area of the mitral valve in the three-chamber view.
MR etiology was degenerative in 19, related to prolapse in 15, a flail leaflet in 25, and functional in 15. Left ventricular ejection fraction was 53%, 55%, 54%, and 27% in the four groups (p < 0.001) and end-systolic volumes were 75, 100, 96, and 224 ml (both comparisons p < 0.001). Mild (RF <30%), moderate (RF 30-39%), and moderate to severe (RF 40-49%) or severe (RF ≥50%) MR was present in 29, 20, and 25 patients. ROA correlated significantly with RF and RV (for both r = 0.80, p < 0.001). ROA ranged from 0.25 to 1.0 cm2 in functional MR, and from 0.1 to 1.58 cm2 in prolapse/flail. The ROA geometry was more slit-like in functional MR than degenerative, prolapse, or flail with a ROA shape index of 3.91 (2.79-4.84) for functional MR compared to 1.24, 2.14, and 2.2 for degenerative, prolapse, and flail. Mitral valve tenting area was greater in functional MR (3.55 ± 1.30 cm2) than in degenerative (1.72 ± 0.41), prolapse (2.0 ± 0.57), or flail (2.15 ± 0.08) MR. Mitral annulus area was larger in functional MR (15.26 ± 4.4 cm2) than in the other three subtypes (8.31, 13.04, and 10.39 cm2) (p < 0.001). The ROA was most commonly circular in the degenerative MR and slit-like in functional MR.
CMR reveals highly variable geometry of the ROA and variable degrees of displacement of the mitral apparatus in patients with MR, dependent on its etiology.
The variability of mitral anatomy, including apical displacement of the leaflets resulting in tenting and distinct geometry of the regurgitant orifice in functional MR versus degenerative and flail etiologies, has previously been described with modern echocardiographic techniques. This study utilized the three-dimensional capability of CMR to identify and quantify the actual short axis of the regurgitant orifice in patients with multiple etiologies of MR. Previous echocardiographic studies have relied on a proximal convergence zone (PISA) for calculation of regurgitant volumes, which in early studies assumed circular geometry of the regurgitant orifice. It has been apparent for a number of years that the regurgitant orifice geometry is frequently noncircular and adjustments need to be made, either with orthogonal views, or more recently, real-time three-dimensional imaging of the surface area of PISA or of the actual regurgitant orifice. In this paper, the authors used CMR to similarly identify the broad range of orifice shape, which ranges from circular to slit-like, with ratios of minor to major axis of the orifice of up to nearly five. Previous studies have pointed out the pitfalls of the ‘eyeball’ approach for quantifying MR with echocardiographic techniques, and the American Society of Echocardiography has recommended that more quantitative techniques be employed. Quantitative ability is intrinsic to CMR, which can provide both high resolution and accurate information regarding the mechanism of MR, as well as its severity.
Keywords: Heart Diseases, Imaging, Three-Dimensional, Mitral Valve Prolapse, Ventricular Function, Left, Mitral Valve Insufficiency, Risk Factors, Magnetic Resonance Imaging, United States, Echocardiography
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