Abstract 4287: Mitral Leaflet Adaptation to Ventricular Remodeling: Prospective Changes in a Model of Ischemic Mitral Regurgitation
Background: Ischemic mitral regurgitation (IMR) is caused by systolic traction on the mitral leaflets related to ventricular distortion. Little is known about how chronic tethering affects leaflet area, in part because it cannot be measured repeatedly in situ. Recently, a new method for 3D echo measurement of mitral leaflet area was developed and validated in vivo against sheep valves, later excised. Clinical studies (n=80) showed that mitral leaflet area increased by >30% in patients with inferior myocardial infarction (IMI) and dilated cardiomyopathy versus normal; greater adaptation independently predicted less MR. This study explored whether mitral valve area changes over time within the same heart with IMR.
Methods: Twelve sheep were studied at baseline and 3 months after IMI by 3D echo and MRI; 6 were untreated and 6 were treated initially with an epicardial patch to limit LV dilatation and MR.
Results: Untreated sheep developed LV dilatation at 3 months with global dysfunction (EF 24±10% vs. 43±11% with patching, p=0.02) and moderate MR (vena contracta 5.0 vs 0.8 mm, p<0.0001). In untreated sheep, total diastolic leaflet area increased from 13.0±1.9 to 18.1±2.5 cm2, p=0.0077. In patched sheep, leaflet area at 3 months was not significantly different from baseline sheep values (12.9±0.9 cm2, p=0.77).
Conclusion: Mitral valve area, independent of systolic stretch, increases over time as the LV remodels after IMI. This increase, however, fails to compensate adequately for tethering to prevent MR. Understanding the mechanism of valve adaptation can potentially suggest new biological and surgical therapeutic targets.