Papillary muscle shortening in the intact dog; a cinderadiographic study of tranquilized dogs in the upright position.

Abstract

Shortening of the anterior papillary muscle of the left ventricle was demonstrated in six intact, tranquilized dogs. Two small metal markers that had been surgically implanted 3-50 months earlier were cineradiographically photographed during approximately ten sequential cardiac cycles in each of two orthogonal positions. Distances between markers were plotted for successive frames. The resulting curves were used to obtain maximum velocities of papillary muscle shortening and lengthening: 1.08 ± 0.29 muscle lengths/sec and 1.39 ± 0.48 muscle lengths/sec, respectively. From the two orthogonal planes, the average maximum spatial distance and the average minimum spatial distance between the markers were calculated. The mean percent shortening of 22.8 ± 6.5% was surprisingly large: it approximated the distance from the foot to the peak of the ascending limb of the myocardial lengthtension curve derived from isolated muscle studies. Mechanical studies on isolated papillary muscle have consistently shown reduced shortening with increasing loads. Since the in vivo dog papillary muscle has been reported to be under considerable tension during systole, there appears to be some contradiction between the degree of shortening found in the present study and the shortening observed in isolated papillary muscle studies. KEY WORDSmvocardial shortening length-tension curves cardiac metal markers myocardial velocities electrocardiogram• Papillary muscle has been investigated for two relatively independent reasons: (1) it is an experimentally convenient sample of ventricular myocardium, and (2) it is a clinically important portion of the functioning heart. Papillary muscle is easy to isolate and to remove from the ventricle. Its small diameter in some species and its participation during cardiac growth also contribute to its utility as an experimental material. Most papillary muscle studies have employed the isolated muscle (1-10), although more recently mechanical properties have been studied in the in situ muscle (11)(12)(13)(14). The essentially linear fiber arrangement within the muscle greatly simplifies the interpretation This work was supported in part by U. S. Public Health Service Grant 1 R01 HL-14651-01 from the National Heart and Lung Institute.A preliminary report on some of these results has been previously presented in abstract form (Fed Proc 27:2699, 1968.Received July 2, 1973. Accepted for publication September 6, 1974. Circulation Research, Vol. 36, January 1975 of data from both mechanical and microscopic studies (15).Papillary muscle function in the intact heart has, most often, been deduced indirectly from isolated muscle studies, clinical observations, autopsy reports, and theoretical considerations. Burch et al. (16) and Burch and Depasquale (17) have postulated that during ventricular systole the papillary muscle, by creating tension, acts as a stay to restrict mitral valve motion. When normal tension development does not occur, excessive mitral valve motion results in mitral regurgitation (the p...

Pathology of myxomatous mitral valve disease in the dog

“…74 Shortening of the papillary muscle throughout left ventricular isovolumic relaxation may contribute to mitral valve opening, while elongation of the papillary muscle during late diastole permits closure of the mitral valve leaflets. 75 …”

Assessment of papillary muscle function in the intact heart.

“…Objections to the accuracy of their measurements have rested on the multiple deficiencies inherent in the techniques used. The ultraminiature strain-gauge transducer used in this study has major advantages: (1) an ability to localize pressure measurements at various depths within the myocardial wall, (2) minimal trauma and distortion of the myocardial tissue at the site of measurement because of the small volume occupied by the sensor, (3) a high frequency response and, (4) 19.20 Conversely, elongation of the papillary muscle in the late portion of diastole appeared necessary to permit proper closure of the leaflets and prevent regurgitation. '9 20 Temporal dissociation between pressure and dimensional changes of the papillary muscle: a load-dependent event.…”

“…3 Others, who evaluated metal clips sewn on the surface of the papillary muscle, found a 22.8% shortening during systole. 4 The availability of miniature probes that produce minimal alterations at the site of measurement has made it possible to assess, in vivo, not only the intra- mural pressure generated within the papillary muscle but also its changes in length. The purpose of this investigation was to describe a technique for the assessment of the performance of the papillary muscle in vivo by measuring the pressure within the papillary muscle and its changes in length throughout the cardiac cycle.…”

Papillary Muscle Function Does Not Predict Mitral Regurgitation in Patients with Normal Left Ventricular Systolic Function: A Transesophageal Echocardiographic Study

“…Human investigations of papillary muscle function and relevance have been limited by small number of subjects, as well as the inherent difficulty of obtaining sufficiently clear images of papillary muscles with transthoracic im-Systolic Function: A Transesophageal Echocardiographic Study aging [5,7,12,13]. Using the superior imaging capabilities of transgastric echocardiography, we evaluated the relationship between papillary muscle function and mitral regurgitation in patients with normal LV chamber size and function and mitral regurgitation.…”