3-DIMENSIONAL DYNAMICS OF THE CANINE MITRAL ANNULUS DURING ISCHEMIC MITRAL REGURGITATION

Background. It has been suggested that ischemic mitral regurgitation r esults, at least in part, from generalized end-systolic mitral annulus (MA) dilatation, but the role of the MA is incompletely understood an d the segmental dynamics of the MA during left ventricular ischemia ha ve not been described. Methods. We used radiopaque markers and simulta neous biplane videofluoroscopy to measure three-dimensional in vivo le ngths of eight MA segments in 7 sedated dogs before and after inductio n of ischemic MR (produced by circumflex coronary artery balloon occlu sion and verified by Doppler echocardiography). As viewed from the lef t atrium, the MA segment between markers 1 and 2 (S-12) was defined as starting at the posteromedial commissure, and remaining segments were numbered sequentially clockwise around the MA (ie, the posterior MA e ncompassed S-12, S-23, S-34, S-45; the anterior MA included S-56, S-67 , S-78, S-81). Marker images obtained 7 to 12 days after implantation were used to construct x, y, and z coordinates of each marker at end-d iastole and end-systole. Results. During regional (posterolateral wall s) left ventricular ischemia, the end-systolic MA area increased (4.9 +/- 0.8 cm(2) [control] versus 5.9 +/- 0.6 cm(2); p = 0.005). End-syst olic MA segment lengths were as follows (control, ischemia [mm, mean a standard deviation]): S-12 = 9 +/- 2, 10 +/- 3; S-23 = 10 +/- 2, 12 /- 3; S-34 = 13 +/- 1, 15 +/- 1; S-45 = 8 +/- 2, 9 +/- 2; S-56 = 11 +/ - 2, 11 +/- 2 S-67 = 12 +/- 2, 12 +/- 2; S-78 = 10 +/- 3, 11 +/- 2; an d S-81 = 11 +/- 1, 12 +/- 1. Values for S-12, S-23, S-34, and S-81 wer e significant (p less than or equal to 0.05 for control versus ischemi a by paired t test). Conclusions. During ischemic mitral regurgitation , the MA enlarged at end-systole, but in an asymmetric manner; most po sterior annular segments lengthened, whereas most anterior annular seg ment lengths did not change. These data suggest that alterations in re gional MA mechanics may be important in the pathogenesis of ischemic m itral regurgitation. Further three-dimensional studies of MA dynamics and shape should be conducted so that new knowledge may result in impr oved mitral valve surgical techniques.