The 4 orientations of MitraClip application were: (1) no clip (baseline); (2) 4.5-mm posterior leaflet × 4.5-mm anterior leaflet; (3) 4.5-mm posterior leaflet × 1.3-mm anterior leaflet; and (4) 4.5-mm posterior leaflet × edge of anterior leaflet.
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Morgan AE, Wozniak CJ, Gulati S, et al. Association of Uneven MitraClip Application and Leaflet Stress in a Finite Element Model. JAMA Surg. 2017;152(1):111–114. doi:10.1001/jamasurg.2016.3360
The MitraClip (Abbott Laboratories) is a percutaneous device for mitral valve (MV) repair, connecting the anterior and posterior leaflets of the mitral valve to eliminate mitral regurgitation (MR). Durability of MitraClip repair is an issue, with a 44% recurrence rate of grade 3 to 4 or higher MR within 2 years of clipping.1 Uneven MitraClip application is a common occurrence, with more posterior than anterior leaflet tissue grasped by the clip.2 To determine whether uneven clipping plays a role in MR recurrence, we investigated the effect of uneven clipping on leaflet stress, which is implicated in repair failure. Leaflets excised after failed MitraClip show significant tissue damage, including large perforations3; furthermore, in vitro studies have shown that increased leaflet stress alters collagen and proteoglycan synthesis, resulting in leaflet thickening and increased compliance.4,5 Leaflet stress after uneven clip application has not been previously studied. To determine whether uneven clipping contributes to increased stress and, therefore, to repair failure, we simulated a variety of MitraClip grasps, testing the hypothesis that uneven grasp does not increase leaflet stress.
A finite element model was created previously, based on imaging of a single human patient with isolated posterior MV prolapse.6 Using this model and the finite element modeling software LS-Dyna (Livermore Software Technology Corp), we applied a simulated MitraClip consisting of virtual sutures, connecting the anterior and posterior mitral leaflets, in 4 orientations: (1) no clip; (2) 4.5-mm posterior leaflet × 4.5-mm anterior leaflet; (3) 4.5-mm posterior leaflet × 1.3-mm anterior leaflet; and (4) 4.5-mm posterior leaflet × edge of anterior leaflet. Von Mises stress (a measure of stress in the x, y, and z directions that gives a complete picture of stress at a given point in a material) was recorded for the anterior and posterior leaflets as the average over the entire leaflet at end systole, over a range of systolic blood pressures from 100 mm Hg to 200 mm Hg. Leaflet coaptation length at end systole was measured for each clip type to ensure that MR was completely eliminated.
Clip application resulted in stable or decreased leaflet stress, relative to the baseline model with no clip. End–systolic leaflet stress increased linearly with increasing systolic blood pressure for all clip configurations (Figure 1). Anterior leaflet stress was higher than posterior leaflet stress for all configurations. Grasp of less anterior leaflet tissue resulted in lower overall leaflet stress. Stress for all clip configurations was concentrated at the area of clip grasp (Figure 2). All clip types restored leaflet coaptation.
In our single-patient model, uneven MitraClip application resulted in lower anterior and posterior leaflet stress over all blood pressures. All clip configurations resulted in stable or decreased stress relative to the model with leaflet prolapse and no clip. Because all clips restored leaflet coaptation, or the normal close contact of the anterior and posterior leaflets during systole, stress in the clip models was shared across a wider surface and was therefore lower than stress in the baseline regurgitant model.
Despite the lower overall stress relative to baseline, all clip configurations resulted in concentrated high stress at the area of clip grasp, a likely contributor to leaflet perforations seen clinically. However, this peak stress was highest in the evenly clipped model (Figure 2).
Although this experiment is only representative of 1 pattern of MV disease, posterior leaflet prolapse is the most common cause of degenerative MR in the developed world, and the MitraClip is approved in the United States only for degenerative MR. Based on this single-patient model, the common procedural occurrence of uneven MitraClip application does not result in increased leaflet stress and therefore should not increase the incidence of recurrent MR. Further studies are indicated to examine these findings in a variety of MV pathologies, including functional MR. As novel percutaneous MV therapies emerge, finite element modeling as used here can be a powerful tool to examine their effect on the tissues of the heart.
Corresponding Author: Mark B. Ratcliffe, MD, Surgical Service (112), San Francisco Veterans Affairs Medical Center, 4150 Clement St, San Francisco, CA 94121 (Mark.Ratcliffe@va.gov).
Published Online: October 5, 2016. doi:10.1001/jamasurg.2016.3360
Author Contributions: Dr Ratcliffe had full access to all the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.
Concept and design: All Authors.
Acquisition, analysis, or interpretation of data: Morgan, Gulati, Ge, Ratcliffe.
Drafting of the manuscript: Morgan, Wozniak, Gulati, Ge, Weinsaft, Ratcliffe.
Critical revision of the manuscript for important intellectual content: Morgan, Wozniak, Gulati, Grossi, Weinsaft, Ratcliffe.
Statistical analysis: Wozniak, Gulati, Ratcliffe.
Administrative, technical, or material support: Wozniak, Ge, Weinsaft, Ratcliffe.
Study supervision: Wozniak, Ge, Grossi, Weinsaft, Ratcliffe.
Conflict of Interest Disclosures: None reported.
Funding/Support: An National Institutes of Health grant (No. R01 HL128278-01) provided salary support for Dr Morgan, who designed the study in conjunction with Dr Ratcliffe and Dr Wozniak; the grant provided further salary support to Dr Weinsaft, who reviewed the manuscript.
Role of the Funder/Sponsor: The National Institutes of Health had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation, review, or approval of the manuscript; and decision to submit the manuscript for publication.
Previous Presentation: This paper was presented at the 2016 Association of VA Surgeons Annual Meeting; April 10, 2016; Virginia Beach, Virginia.
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