DYNAMICS OF NORMAL AND ISCHEMIC CANINE PAPILLARY-MUSCLES

This investigation was designed to elucidate the dynamics of the left ventricular (LV) papillary muscles. Miniature tantalum myocardial mark ers were placed on the tip and base of each papillary muscle in six do gs. Markers were also implanted into the LV myocardium to define two o rthogonal equatorial diameters and the long-axis dimension. Two weeks later, after recovery from thoracotomy, markers were visualized by bip lane fluoroscopy, and video images were recorded during control condit ions, after autonomic blockade, after inotropic stimulation with calci um, after methoxamine infusion (to increase afterload), and after bloo d volume augmentation (to increase preload). Two days later, radiograp hic recordings were made before and after occlusion of the left circum flex coronary artery. Computer-aided analysis of the video recordings was used to determine three-dimensional coordinates of the markers. It was found that before circumflex coronary occlusion, the dynamics of both papillary muscles closely mimicked the dynamics of the LV as a wh ole. The papillary muscles shortened during ejection and lengthened du ring diastole. Their lengths changed minimally during the isovolumic p eriods, and this behavior was not altered by any of the interventions except coronary occlusion. During circumflex coronary artery occlusion , the ischemic posterior papillary muscle lengthened during isovolumic contraction and most of ejection and shortened only when LV pressure began to fall. Hence, we believe that previous studies demonstrating p apillary muscle lengthening during isovolumic contraction and shorteni ng during isovolumic relaxation may have been confounded by coexistent myocardial ischemia or stunning.