PAPILLARY-MUSCLE - LEFT-VENTRICULAR WALL COMPLEX

Objectives. Mitral valve homografts, despite theoretical advantages, a re not widely used, in part because of lack of basic information about the three-dimensional geometry of the mitral apparatus, Methods: Radi opaque markers were used in the study of eight closed-chest dogs under four conditions: (1) baseline, (2) caval occlusion, (3) tachycardia ( atrial pacing), and (4) nitroprusside infusion, Using a cylindrical co ordinate system, defined with the origin at the midpoint between the a nterior and posterior commissures, and the left ventricular long arris (z-axis), defined by the origin and the left ventricular apex, D-TIP- MA (the z-coordinate [millimeters] of the papillary muscle tip), was m easured at 10 time points throughout the entire cardiac cycle, D-BASE- MA (the z-coordinate of the papillary muscle base) and I-PM (the lengt h of the papillary muscle [millimeters]) were also measured, Results: D-TIP-MA varied slightly with time (p < 0.001 by analysis of variance) , but the magnitude of change was negligible (< 0.9 mm) (e.g., D-TIP-M A of the anterior papillary muscle was 20.7 +/- 2.7/20.8 +/- 2.8 [end- diastolic/end-systolic, mean +/- 1 standard deviation]; D-TIP-MA of th e posterior papillary muscle was 25.8 +/- 4.8/25.5 +/- 4.5), D-TIP-MA was minimally influenced by the above perturbations. D-BASE-MA and I-P M of each papillary muscle, however, changed throughout the cardiac cy cle (p < 0.001 by analysis of variance) by about 3 mm, and both parame ters were dependent on loading conditions, Conclusions. Papillary musc le length changed to keep the D-TIP-MA distance constant such that the papillary muscle and left ventricular wall functioned together as a u nit (''J-shaped complex''), These results provide a physiologic ration ale for measuring D-TIP-MA, define its potential surgical usefulness, and imply that using the entire length of the donor's papillary muscle (i.e., maintaining the entire J-shaped complex) is important in opera tions in which homograft or stentless xenograft mitral valves are used .