Excitability and Electrical Activity of Human Myocardial Strips from the Left Atrial Appendage in Cases of Rheumatic Mitral Stenosis

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Abstract
In isolated strips of human left atrium, ob tamed during commissurotomy for rheumatic mitral stenosis, recordings of the electrical action phenomena were made and determina tiorms of the resting excital)ility amid of the ex citability cycle were carried out. Two of the four strips did not show any appreciable spontaneous electrical activity and were found to be inexcitable by applied current pulses. These strips were obtained from pa tients in whom permanent or temporary atrial fibrillation existec1 prior to operation, and in whom the left atrial appendage was grossly dilated. In the two other strips, obtained from patients with a sinus rhythm prior to opera tion and with left atrial. appendages of ap proximately normal size, determinations of strength/duration and strength/interval re quirements, together with the recorded com plexes, demonstrated the occurrence of a functional dissociation between various elements in these muscle strips, which increased during the refractory period. This functional dissociation is thought to be related to the development of connective tissue between the muscle fibers, observed by microscopic exam ination, and due to the rheumatic process. Its significance in the genesis of atrial arrhyth mias in cases of mitral stenosis is discussed. Strophanthin in a concentration of 10-8 was found to shorten the refractory period and to cause a lowering of the resting threshold for stimuli with a duration of less than 5 msec., and a rise in the threshold for larger stimuli.

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