In Vivo Activity of the Right Ventricular Papillary Muscles 1

Abstract

Summary

Strain gauge recordings of in situ right ventricular papillary muscle behavior demonstrate their active contraction in well programmed coordination with other portions (conus, sinus, and right interventricular septal wall) of the right ventricle. Their activity is not directly associated with contraction of anterior epicardial segments of the left ventricle, but is associated with right ventricular sinus contraction. Electrical excitation of the right stellate ganglion elicits clear and discrete augmentation of the right ventricular papillary muscles while comparable excitation of the left stellate induces significantly lesser responses. Responses to positive inotropic agents (norepinephrine, isoproterenol) are sharp and strong while changes in activity accompanying afterloading (neosynephrine, coarctation of pulmonary artery and the aorta) and preloading (rapid saline infusion) are less intense. Alterations in contractile patterns, particularly those associated with time of onset of contraction, are closely associated with similar events in the sinus region, but are often divorced from simultaneous behavior of the conus. In clear distinction from the left ventricle in which papillary muscle contraction occurred concurrently with elevation in intraventricular pressure, the papillary muscles of the right ventricle contract some 10 to 20 msec before intraventricular pressure begins to rise.