Electrical Activation and Mechanical Asynchronism in the Cardiac Cycle of the Dog

Abstract

With the technical a.s.ii.ituiice of Willium H. Meyer, Jr., M.U., uud Louix Lmnberg, M.IJ. Right mid left ventricular pressure curves and electrocardiogram were recorded in the dog during sinus rhythm and during mechanically induced right and left ventricular premature systoles. The normal range during sinus rhythm for the relationship between onset of right and left ventricular contraction was determined. At one extreme, right ventricular contraction commenced 0.02 second before the left; at the other extreme, left ventricular contraction started 0.03 second before the right. In most instances, the onsets of ventricular contraction were either temporally identical or one ventricle contracted 0.01 second prior to the other. DISSOCIATION of electrical and mechanical events in the cardiac cycle has been reported by several observers.1 ' 3 Previous studies 4 have suggested that electrical ventricular asynchronism (complete bundle branch block, ventricular premature beats, WolffParkiiison-White Syndrome, and complete heart block with idioventricular rhythm) does not necessarily lead to mechanical ventricular asynchronism in onset of ventricular contraction. However, divergent data have been presented. 5 The literature pertaining to this subject has recently been summarized.' Supported in part by a grant from the V.S. Public Health Service and the National Heart Institute (H-2735) and a grant from the Florida Heart Association.Presented in part at the eightieth annual meeting of the American Physiology Society, Philadelphia, April, 1958.Dr. Litwak is an Investigator, Howard Hughes Medical Institute.Dr. Meyer is a Trainee, Xational Heart Institute. Received for publication October 22, 1958. evidence only. In two studies in man direct recording of right and left ventricular pressure curves was performed. Brannwald and Morrow 7 performed simultaneous right and left heart catheterization in 15 patients with complete bundle branch block (5 with left bundle branch block, and 10 with right bundle branch block). Asynchronous contraction of the two ventricles was absent in all 5 patients with left bundle branch block and 6 with right bundle branch block. Samet et al. 6 have recorded right and left ventricular curves during 100 ventricular premature beats obtained in the course of simultaneous right and left heart catheterization. Mechanical asynchronism in onset of ventricular isometric contraction was found in only 28 of 100 ventricular premature systoles with widened aberrant QRS complexes.The present study was designed to extend to the dog these observations on the mechanics of ventricular contraction during ventricular premature complexes. The presence of catheters within the lumen of the right and left ventricle in the study of man could theoretically obscure mechanical asynchronism by endocardia] stimulation near the interventricular septum. METHODSSimultaneous right and left ventricular pressure curves were registered in 31 dogs under barbiturate anesthesia (pentobarbital sodium, 30 mg./Kg.,

Influence of the Cardiac Sympathetics on Synchrony of Ventricular Contraction.

“…In spite of the early appearance of epicardial potentials on the anterior wall of the right ventricle, and despite the relatively smaller muscle mass to be excited in the right ventricle, the initial ventricular pressure rise was invariably observed in the left ventricle under control conditions of these experiments. This consistency in the earlier pressure rise in LV contrasts with that reported by Samet et aZ (8) and Di Bartolo et aZ (9) who observed the initial rise in pressure to occur simultaneously or either in right or left ventricle. In both reports, however, illustrative traces and speed of recording would seem to make precise measurements difficult.…”

Alterations in Cardiac Synchrony Induced by the Cardiac Sympathetic Nerves

“…While measuring pressures simultaneously within the two ventricles of the dog heart, Samet et al 2 and Di Bartolo et al 3 reaffirmed observations of Katz 4 that the initial pressure rise during systole may occur first in either the right or left ventricle, or that it may appear in both simultaneously. Similar conclusions have been drawn concerning ventricular synchronism in man.…”