LOSS OF 3-DIMENSIONAL CANINE MITRAL ANNULAR SYSTOLIC CONTRACTION WITHREDUCED LEFT-VENTRICULAR VOLUMES

Background We have recently described an inhomogeneous pattern of syst olic contraction of the mitral annulus (MA) in normovolemic dogs: the posterior annulus shortens, and the anterior annulus lengthens. MA dyn amics, however, have not been studied in volume-depleted hearts. Metho ds and Results Eight radiopaque markers were placed equidistant from e ach other around the MA in seven dogs. As viewed from the left atrium, the segment between markers 1 and 2 (seg(12)) began at the posteromed ial commissure, and remaining segments were numbered sequentially cloc kwise around the MA (ie, posterior MA encompassed seg(12), seg(23), se g(34), and seg(45); anterior MA encompassed seg(56), seg(67), seg(78), and seg(81)). Marker images were obtained in sedated dogs by simultan eous biplane videofluoroscopy 7 to 12 days after marker implantation, and three-dimensional marker coordinates at end diastole (ED) and end systole (ES) were computed. Vena caval occlusion (VCO) was used to red uce left ventricular end-diastolic volume to 70+/-5% of baseline (BL). With VCO, mean MA area did not change from ED to ES (3.4+/-0.8 versus 3.6+/-0.7 cm(2), P=NS) during the cardiac cycle. MA segmental systoli c shortening values (negative values indicate lengthening) were as fol lows for BL and VCO, respectively (mean+/-SD): seg(12), 7+/-9% and 0+/ -13%; seg(23), 8+/-10% and 1+/-11%; seg(34), 16+/-6%* and 4+/-9%; seg (45), 10+/-7% and 2+/-13%; seg(56), -4+/-5%* and -16+/-11%*; seg(67), -7+/-7%: and -14+/-7%*; seg(78), 3+/-2%* and -1+/-6%; and seg(81), 6 +/-5% and -5+/-11% (*P less than or equal to.05 versus zero changes, paired t test). Conclusions With acute volume depletion, the five annu lar segments that shortened at BL no longer changed length; two anteri or segments (seg(56) and seg(67)) that lengthened at BL continued to l engthen significantly, and to a greater extent. These findings indicat e that the anterior MA is a more dynamic structure than previously tho ught. Such dynamic motion may be important for normal mitral valvular function and possibly needs to be taken into account in the design of mitral valve reparative techniques.