Total Excitation of the Isolated Human Heart

Abstract

SUMMARYTo obtain information conceming the time course and instantaneous distribution of the excitatory process of the normal human healt, studies were made on isolated human hearts from seven individuals who died from various cerebral conditions, but who had no history of cardiac disease. Measurements were made from as many as 870 intramural terminals.In the isolated human hearts three endocardial areas were synchronously excited o to 5 msec after the start of the left ventricular activity potential. These areas increased rapidly in si ze dUl'ing the next 5 to 10 msec and became confluent in 15 to 20 msec. The left ventricular areas Rrst excited were (1) high on the anterior paraseptal wall just below the attachment of the mitral valve; (2) central on the left surface of the interventricular septum and (3) posterior paraseptal about one third of the distance from apex to base. The last part of the left ventricle to be activated usually was the posterobasal area. Endocardial activation of the right ventricle was found to start ne ar the insertion of the anterior papillary muscle 5 to 10 msec af ter onset of the left ventricular cavity potential. Septal activation started in the micldle third of the left side of the interventricular septurn, somewhat anteriorly, and at the lower third at the junction of the septum and posterior wall. The epicardial excitation pattem reflected the movements of the intramural excitation wave. Conduction velo city was determined in one heart by an appropriate stimulation technic. Atrial excitation, explored in two hearts, spread more or less according to concentric isochronic lines. Control studies, carried out on Rve canine hearts, disclosed that the pattem of ventricular excitation did not change af ter isolation and perfusion. However, total excitation was completed earlier in the isolated heart, and conduction velo city increased.Careful mapping illustrations are presented.Additional Indexing W ords:Ventricular excitation Intramural conduction velo city Epicardial excitation Atrial excitation K NOWLEDGE of the time course and instantaneous distribution of the excitatory pro ce ss of the normal human heart would be of value for an understanding of the QRS complex.Studies of this process during surgical intervention for heart disease or pulmonary

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