A Novel Quantitative Ex-Vivo Model of Functional Mitral Regurgitation
Chetan Pasrija, Rachael Quinn, Mehrdad Ghoreishi, Felino V Cortez, Michael N D'Ambra, James S Gammie
University of Maryland, Baltimore, MD
OBJECTIVES: Durability of mitral valve (MV) repair for functional mitral regurgitation (FMR) remains suboptimal with a recent randomized study reporting a 60% recurrence of moderate MR by 2 years when utilizing conventional annuloplasty techniques. While there is an intense need for improved interventions that result in a durable repair, there remains a limited ability to test and quantify these repair strategies in an ex-vivo setting prior to large animal or clinical studies. We sought to create a highly reproducible, quantitative model of FMR that reproduces the annular and valvular changes seen in patients with significant FMR.
METHODS: MV geometry in FMR patients undergoing 3D ultrasound assessment was used to create the ex-vivo model design. Utilizing fresh swine hearts (478 (IQR:431-504) grams) from a commercial abattoir, a cannula was placed through the aortic valve, and the left ventricle was pressurized with air to maintain a static pressure of 120mmHg. The left atrium was excised and the MV imaged in the normal state. FMR was then created by radially dilating the annulus with 8-10 equally placed annular sutures, and displacing the papillary muscle tips apically and radially in a calibrated fashion. Dilation of the annulus and displacement of the chordae was continued in a stepwise fashion until coaptation was exhausted. Imaging was performed utilizing a 3D structured-light scanner, which records 3D structure, texture, and color of the mitral valve with accuracy approaching 0.05mm. Finite element analysis and dimensional quantification was performed using scan-to-CAD software (Figure 1).
RESULTS: 7 swine hearts were imaged in control and FMR states. Compared to control, the antero-posterior diameter in the FMR model increased 36% (2.5 vs. 3.4cm, p=0.002) while the commissural diameter remained unchanged (3.3 vs. 3.3cm, p=0.516) (Table 1). There was a consequent 35% increase in annular area (p=0.004). While the anterior annular circumference remained fixed, the posterior circumference increased by 23% (p=0.018), indicating an isolated posterior dilation of the valve. Moreover, the annulus became less "saddle-shaped," evidenced by a 46% decrease in the annular height (p=0.035) and 10◦ increase in the nonplanarity angle (p=0.011) (angle between plane of posterior annulus and A2). Assessment of the valve demonstrated a 32% increase in tenting height (8.7 vs. 11.5mm, p=0.013) with a corresponding 79% increase in tenting area (126 vs. 226mm2, p=0.007). While the non-coaptating surface area of the anterior and posterior leaflet increased by 20% (p=0.018) and 67% (p=0.006), respectively, after creating FMR, coaptation surface area decreased by 66% (p=0.012).
CONCLUSIONS:This novel quantitative ex-vivo model provides a simple, reproducible, inexpensive, and accurate benchtop representation of FMR that mimics the geometric changes occurring clinically. Utilizing this model, new FMR surgical repair techniques can be subject to quantitative 3D analysis and optimized prior to large animal and clinical studies.
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