Effects of Undersized Mitral Annuloplasty on Regional Transmural Left Ventricular Wall Strains and Wall Thickening Mechanisms

Abstract

Background-Undersized mitral annuloplasty, widely used for ischemic and functional mitral regurgitation (MR), has been proposed as an "annular solution to a ventricular problem." Beyond relief of MR, it is thought to improve global left ventricular (LV) shape, hence potentially reducing myocardial stress and promoting beneficial reverse LV remodeling. We previously observed that undersized annuloplasty inhibited systolic wall thickening at the LV base near the mitral annulus. In this study, we measured the effects of undersized annuloplasty on regional transmural LV wall fiber and sheet strains and wall thickening mechanisms. Methods and Results-Nine sheep had transmural radiopaque beadsets surgically inserted into anterobasal and lateral equatorial LV regions, with additional markers silhouetting the LV and mitral annulus. 4-Dimensional marker dynamics were studied with biplane videofluoroscopy before and after tightening an adjustable Paneth-type mitral annuloplasty suture. Transmural circumferential, longitudinal, and radial systolic and remodeling strains in the subepicardium (20% depth), midwall (50%), and subendocardium (80%) in both regions were computed. Fiber and sheet angles from quantitative regional histology allowed transformation of these strains into local fiber (f), sheet (s), and sheet-normal (n) coordinates. Further analysis calculated the transmural contributions of sheet extension (E ssc ), sheet thickening (E nnc ), and sheet shear (E snc ) to systolic wall thickening (E 33 ). In the anterobasal region, undersized annuloplasty reduced systolic wall thickening (E 33 ) by Ϸ50% at all transmural depths by inhibiting: (1)

Effect of local annular interventions on annular and left ventricular geometry☆☆☆

“…We observed papillary muscle repositioning with this intervention, and it is not unreasonable to conjecture that such would also be the effect of the Geoform prosthesis consistent with improved coaptation borne out in mathematical modeling studies [13]. Undersized suture annuloplasty with 20% SL diameter reduction, however, has been associated with reduced anterobasal myocardial fiber shortening in experimental animals [21] suggesting a possible deleterious effect on local LV function. Similarly, isolated SL cinching of the central valve diameter reduces LV systolic wall thickening near the mitral annulus [22].…”

Impact of Left Ventricular to Mitral Valve Ring Mismatch on Recurrent Ischemic Mitral Regurgitation After Ring Annuloplasty

“…Experimental studies have demonstrated increased strains on the posterior annulus and leaflet following restrictive annuloplasty which further predisposes to leaflet immobility and tethering. 18, 19, 25, 26 …”

Dynamic 3-Dimensional Echocardiographic Assessment of Mitral Annular Geometry in Patients With Functional Mitral Regurgitation

“…Data from animal studies has been used to improve annuloplasty ring design but technological limitations have precluded the performance of such analyses for routine clinical use 38 . Our performance of these analyses in a timely fashion brings us a step closer to incorporating this information into clinical decision-making and objectively assessing the concept of offering an ‘annular solution to a ventricular problem’ 19 .…”

“…Ideally, geometric distortion of the mitral annulus incurred from annuloplasty devices should also be objectively quantified and followed. But despite recognition of the prognostic value of mitral annular changes in FMR, technological impediments have precluded their clinical application 19 . Demonstration of differences in mitral annular geometry (static and dynamic) between patients with and without FMR in a clinically feasible fashion should be the first step towards achieving this goal.…”