Ann Thorac Surg 2007;84:101-102
© 2007 The Society of Thoracic Surgeons
Original Articles: Cardiovascular
Invited commentary
Mark B. Ratcliffe, MD
Surgical Service (112), San Francisco Veterans Affairs Medical Center, 4150 Clement St, San Francisco, CA 94121
(Email: mark.ratcliffe{at}med.va.gov).
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Introduction
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In the article by Votta and colleagues [1], the authors extend their previous finite element simulation of dog bone-shaped mitral annuloplasty treatment of functional mitral regurgitation (MR) [2] to include simulation of the GeoForm Ring and Physio Annuloplasty Ring (Carpentier-Edwards, Irvine, CA) [1]. The authors show that the GeoForm (Carpentier-Edwards) shape makes the mitral valve unlikely to develop recurrent MR if further left ventricular (LV) remodeling occurs.
Wu and colleagues [3] previously found no effect of mitral repair on mortality in a group of patients with ejection fraction <30% and patients with severe MR operated on between 1992 and 2004. Using the same group of patients, Spoor and colleagues [4] found that patients who received flexible rings, which were more commonly used before the year 2000, were more likely to have recurrent MR develop (9.4%). Although the incidence of mitral reoperation in patients who received a rigid ring in that study was low (<1%) [4], the obvious hope is that the Geoform valve (Carpentier-Edwards) with its reduced septolateral dimension and rigid titanium core will abolish recurrent MR after mitral repair of functional MR, and that it will allow separation between the mitral repair and medical therapy groups in subsequent clinical studies.
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Value of Finite Element Simulations
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Animal studies using the sheep model of ischemic MR [5] for testing the mitral valve in ex vivo flow loops [6] have added to our understanding of functional MR. The study by Votta and colleagues [1] and the prior study by Maisano and colleagues [2] now show that finite element simulation of the mitral valve is a powerful new tool that has the potential to add significant new knowledge about the mechanics of functional MR and mitral valve repair.
Finite element modeling of the mitral valve has been previously done by Kunzelman and colleagues [7] and by Salgo and colleagues [8], and certainly finite element modeling is the only way to accurately calculate stress in the mitral leaflets and annulus. Hopefully in the future, ventricular contraction [9] can be added to mitral models so that contraction of the annulus and realistic movement of the papillary muscles during systole can be incorporated.
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The Hump
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Perhaps the most controversial aspect of the Geoform ring is the accentuated posterior hump. It should be noted that the planar dog bone annuloplasty shape as tested by Maisano and colleagues [2] was also unlikely to develop recurrent MR with further LV remodeling. Therefore, it is the reduction in septolateral dimension, that makes the Geoform ring insensitive to further remodeling, and the hump probably adds little in this regard.
The posterior hump may have other effects. First, the "saddle" mitral annular shape that the Geoform ring produces may distribute chordal stresses more equally [6]. On the other hand, although the authors did not calculate stress on the annulus, stress in the area of the hump is almost surely increased, and ring dehiscence in this area is possible.
A second stated goal of the Geoform is to alter LV size and shape. Tibayan and colleagues [10] have previously noted that an undersized mitral ring reduces the circumflex radius of curvature at the base and equator of the heart. It remains to be seen whether the mechanical effect of the Geoform ring on the annulus has a significant effect on the left ventricle [11]. It should be noted that early results from a clinical trial to assess the effect of the Geoform annuloplasty ring on LV shape found a reduction in mitral tenting height as well as reductions in LV end-diastolic volume and sphericity 6 months after mitral repair [11]. However it is not clear whether a planar ring would have had a different effect.
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Does Mitral Repair Effect Remodeling?
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Recent studies in sheep by Guy and colleagues [12], in which prophylactic mitral valve repair had no effect on LV remodeling after posterobasal myocardial infarction, and the previous study by Wu and colleagues [3] in humans, in which mitral valve repair failed to improve survival, suggest that mitral valve repair stops but does not reverse the LV remodeling associated with functional MR. The Geoform ring is a creative attempt to effect LV remodeling directly by the effect of the ring on the ventricular wall and by preventing the volume load associated with recurrent MR. However, a randomized trial of medical therapy with and without mitral repair in patients with functional MR will be necessary to determine whether mitral repair has a beneficial effect on LV size and patient survival.
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References
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- Votta E, Maisano F, Bolling SF, Alfieri O, Montevecchi FM, Redaelli A. The Geoform disease-specific annuloplasty system: a finite element study Ann Thorac Surg 2007;84:92-102.[Abstract/Free Full Text]
- Maisano F, et al. An annular prosthesis for the treatment of functional mitral regurgitation: finite element model analysis of a dog bone-shaped ring prosthesis Ann Thorac Surg 2005;79:1268-1275.[Abstract/Free Full Text]
- Wu AH, Aaronson, Bolling, et al. Impact of mitral valve annuloplasty on mortality risk in patients with mitral regurgitation and left ventricular systolic dysfunction J Am Coll Cardiol 2005;45:381-387.[Abstract/Free Full Text]
- Spoor MT, Geltz A, Bolling SF. Flexible versus nonflexible mitral valve rings for congestive heart failure: differential durability of repair Circulation 2006;114(1 Suppl):I67-I71.[Medline]
- Llaneras MR, et al. Large animal model of ischemic mitral regurgitation Ann Thorac Surg 1994;57:432-439.[Abstract]
- Jimenez JH, et al. Effects of a saddle shaped annulus on mitral valve function and chordal force distribution: an in vitro study Ann Biomed Eng 2003;31:1171-1181.[Medline]
- Kunzelman KS, et al. Finite element analysis of the mitral valve J Heart Valve Dis 1993;2:326-340.[Medline]
- Salgo IS, et al. Effect of annular shape on leaflet curvature in reducing mitral leaflet stress Circulation 2002;106:711-717.[Abstract/Free Full Text]
- Guccione JM, McCulloch AD. Mechanics of active contraction in cardiac muscle: part I—constitutive relations for fiber stress that describe deactivation J Biomech Eng 1993;115:72-81.[Medline]
- Tibayan FA, et al. Undersized mitral annuloplasty alters left ventricular shape during acute ischemic mitral regurgitation Circulation 2004;110(11 Suppl 1):II98-II102.[Medline]
- Bolling S, et al. Reforming LV geometry in CHF with MR: a unique valvular solution for a ventricular problem. San Francisco: American Association of Thoracic Surgery; 2005.
- Guy TS, et al. Prevention of ischemic mitral regurgitation does not influence the outcome of remodeling after posterolateral myocardial infarction J Am Coll Cardiol 2004;43:377-383.[Abstract/Free Full Text]
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The Geoform Disease-Specific Annuloplasty System: A Finite Element Study
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Ann. Thorac. Surg. 84: 92-101.
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Introduction
Value of Finite Element...