Atrial Myocardium Transplanted in Right Ventricle

Abstract

As a corollary to study of the adequacy of atrial grafts as right ventricular roofs in tetralogy of Fallot, physiologic and histologic characteristics of such transplanted myocardium were studied. Atrial grafts were transplanted in 10 6-week-old dogs. Seven surviving animals were sacrificed after 21 months. Strips of myocardium, 1 x 1 x 11 mm., from the autograft, left atrium and right ventricle were compared as to autonomicity, passive length: tension, active length:tension, frequency:force, time to peak tension, time to one half relaxation, electrocardiogram and histologic characteristics. Growth of the graft was also measured. Grafts and atria displayed autonomicity, whereas ventricles did not. Grafts beat autonomously from 21-72 beats/minute. Active and passive length-tension relationships were qualitatively similar in all types of myocardium, with patches having lower active and higher passive tensions than atrium and ventricle. Contractile force in the patch increased as a function of increasing frequency, passed through an optimun and then decreased; in atrium and ventricle force continuously decreased. Time to peak tension and to one half relaxation were similar in all specimens. Electrocardiogram was grossly normal but conduction in the patch was abnormal going from epicardium to endocardium. Grafts displayed histologic alterations generally characterized by invasion of fibrocartilagenous elements between healthy myocardial fibers. These grafts decreased by about 20% in area over the 21 month postoperative period.