Tom C. Nguyen1, Akinobu Itoh1, Robert A. Oakes1, Tomasz A. Timek1, Daniel B. Ennis1, David Liang1, George T. Daughters2, Neil B. Ingels2, David C. Miller1; 1Stanford University, Stanford, CA; 2Research Institute of the Palo Alto Medical Foundation, Palo Alto, CA
Objective: Chronic ovine ischemic MR is associated with mitral annular dilatation predominately in the septal-lateral dimension. Whether these perturbations are due to the ischemic insult or the MR per se (or both) is unknown. In an attempt to isolate these two variables, we investigated the effects of "pure" chronic (non-ischemic) MR on annular dynamics.Methods: Eight radiopaque markers were sutured equidistant around the mitral annulus in sheep randomized to control (CTRL, n=5) or experimental (EXP, n=9) groups. In the EXP group, a 2.8mm to 4.8mm hole was created in posterior mitral leaflet to generate moderate-severe mitral regurgitation. 4-D marker coordinates were obtained throughout the cardiac cycle 1 and 12 weeks postoperatively. Mitral annular area (MAA), annular septal-lateral (SL) and commissure-commissure (CC) dimensions, and segmental distances between each annular marker were calculated every 16.7ms.
Results: MR grade was 0.4±0.2 in CTRL and 3.2±0.5 in EXP (p<0.001) at 12 weeks. At 12 weeks, LV mass index (145±10 vs 167±13g/m2), EDVI (107±31 vs 148±44 ml/m2) and ESVI (61±19 vs 92±28 ml/m2) were larger in the EXP group (all p< 0.001). MAA, SL and CC distance at 1 and 12 weeks were compared throughout the cardiac cycle (time 0 = ED, see Figure): Note the significant difference in CC dimension at 12 weeks (bottom right), but no difference in the SL dimension at 12 weeks (bottom center). Fibrous mitral annular perimeter at ED and ES was also larger in the EXP group at 12 weeks (ED 22.3±3.7 vs. 26.5±3.3 mm; ES 23.4±3.6 vs. 27.9±3.8 mm [both p<0.001]); surprisingly, there was no difference in muscular (posterior) mitral annular perimeter.
Conclusion: In contrast to dominant SL dilatation and muscular annular elongation observed with chronic ischemic MR, "pure" chronic (non-ischemic) MR was associated exclusively with an increase in the CC dimension and fibrous annular perimeter. These data suggest that infarction is a more important determinant of SL dilatation than is LV volume overload, which reinforces the need for disease-specific designs of annuloplasty rings.
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