Dissimilar length-tension relations of canine ventricular muscle and false tendon: Electrophysiologic alterations accompanying deformation

Abstract

Length-passive tension (strain-stress) relations were determined in right ventricular trabeculae and right and left ventricular false tendons removed from dog hearts. Preparations were isolated in tissue bath (1 Hz; 36°C) and resting length was progressively increased. False tendons are more compliant than ventricular muscle, requiring a greater increase in length to reach a specified resting tension. The difference in compliance was significant ( P < 0.05) at extensions of 40% or more. Right ventricular false tendons are slightly more compliant than left ventricular false tendons; the differences become significant ( P < 0.05) at an extension of 40%. The apex of the length-active force relation occurred at greater extensions in false tendon. Scanning electron microscopy demonstrates that extensions of 40 to 50% orient contractile elements uniformly parallel in ventricular muscle while in false tendon undulations remain at these extensions. Stretch caused alterations in resting and action potentials (during stimulation at 1 Hz) of seven false tendons studied with microelectrodes (three of the false tendons demonstrated automatic rhythms) and four of six ventricular muscles. The strains at which the electrical changes occurred were similar in muscle and false tendon (∼65%).