Does annular reduction decrease regional circumferential LV radius of curvature in a sheep model of acute ischemic mitral regurgitation?
In an acute sheep model of ischemic mitral regurgitation, undersized mitral annuloplasty decreased end-systolic left ventricular radius of curvature, potentially reducing LV wall stress.
BACKGROUND: Underlying left ventricular (LV) dysfunction contributes to poor survival after operation to correct ischemic mitral regurgitation (IMR). Many surgeons do not appreciate that a key component of the Bolling undersized mitral ring annuloplasty concept is to decrease LV wall stress by altering LV shape, but precise 3-dimensional (3-D) geometric data do not exist substantiating this effect. We tested the hypothesis that annular reduction decreases regional circumferential LV radius of curvature (ROC) in a model of acute IMR. METHODS: Eight adult sheep underwent insertion of an adjustable Paneth-type annuloplasty suture and radiopaque markers on the LV and mitral annulus. The animals were studied with biplane videofluoroscopy during baseline conditions, then before and after tightening the annuloplasty suture during proximal left circumflex occlusion. End-systolic circumferential regional LV ROC and mitral annular area were computed. RESULTS: Acute IMR was eliminated (MR grade 2.1+/-0.4 to 0.4+/-0.4, mean+/-SD, P<0.05) by tightening the Paneth annuloplasty suture. Paneth suture tightening during circumflex occlusion also decreased end-systolic regional circumferential radii of curvature at the basal (anterior, 3.40+/-0.16 to 3.34+/-0.14 cm; posterior, 3.31+/-0.23 to 3.24+/-0.26 cm; P<0.05) and equatorial levels (anterior, 2.99+/-0.21 to 2.89+/-0.29 cm; posterior, 2.86+/-0.38 to 2.81+/-0.41 cm; P<0.05). CONCLUSIONS: Acute proximal circumflex occlusion caused IMR and increased end-systolic LV radii of curvature in this experimental preparation. Annular reduction sufficient to abolish IMR also decreased end-systolic anterior and posterior LV ROC, which would be expected to reduce LV wall stress and oxygen consumption in these regions, both potentially beneficial effects. The long-term effects of undersized annuloplasty on LV remodeling and function, however, will require further study in chronic animal preparations or patients with chronic IMR.
Tibayan et al. (2004) studied this question.