3-DIMENSIONAL REGIONAL DYNAMICS OF THE NORMAL MITRAL ANULUS DURING LEFT-VENTRICULAR EJECTION

The mitral anulus is a dynamic structure that undergoes alterations in size and shape throughout the cardiac cycle, contracting during systo le, Numerous reports have shown this systolic orifice reduction to be due chiefly to posterior annular contraction, whereas the anterior per imeter was unchanged, Segmental motion of the mitral anulus from true in vivo three-dimensional data, however, has not been described, We us ed radiopaque markers and simultaneous biplane videofluoroscopy to mea sure the lengths of mitral anular segments in seven closed-chest, seda ted dogs, Eight markers were placed equidistant from each other around the mitral anulus, As viewed from the left atrium, segment 1 began at the posteromedial commissure, and the remaining segments were numbere d sequentially clockwise around the anulus (that is, the posterior mit ral anulus encompassed segments 1 to 4 and the anterior anulus encompa ssed segments 5 to 8), Marker image coordinates obtained from two orth ogonal views 7 to 12 days after implantation were merged to construct three-dimensional marker coordinates at end-diastole and end-systole. From end-diastole to end-systole, mean annular area decreased by 11% /- 8% (5.5 +/- 0.9 cm(2) to 4.9 +/- 0.8 cm(2), p = 0.005) and perimete r by 5% +/- 4% (8.8 +/- 0.7 cm to 8.3 +/- 0.7 cm, p < 0.01), Mitral an nular segmental percent systolic shortening (negative values indicate lengthening) were as follows (mean +/- standard deviation): segment 1, 7% +/- 9%; segment 2, 8% +/- 10%; segment 3, 16% +/- 6%; segment 4, 1 0% +/- 7%; segment 5, -4% +/- 5%; segment 6, -7% +/- 7%; segment 7, 3% +/- 2%; and segment 8, 6% +/- 5%, With the exception of segment 1, al l posterior (2 to 4) and two anterior (7 and 8) mitral annular segment s contracted significantly (p less than or equal to 0.05 vs zero, pair ed t test), Two anterior annular segments (5 and 6, regions overlappin g aortic-mitral continuity), however, unexpectedly lengthened during l eft ventricular systole, We conclude that the anterior mitral anulus m ay be a much more dynamic component of the mitral apparatus that previ ously thought, Such heterogeneous dynamic annular motion should be tak en into account when various mitral valve reparative techniques are be ing designed.