Burchell, Howard B.

The spread of the excitatory process in the ventricular septum of the dog's heart has been studied in the isolated organ perfused by the Langendorff technic. It has been possible to remove large portions of the free wall of the right and left ventricles and explore the septal surfaces under direct vision. The mean excitatory pathway in the muscular mass of the dog's ventricular septum has been demonstrated to be from apex to base. The left side of the septum is activated before the right side, and the apical part of the right side is activated before its base.

On isolated perfused canine hearts, studies were made of the electrocardiographic changes which attend injury to the endocardium of the free wall of the left ventricle and of changes which develop following extension of the injury onto the left ventricular aspect of the septal endocardium. In an epicardial lead, the depression of RS-T segment produced by a subendocardial injury of the free wall of the left ventricle disappeared almost completely when that same type of injury was extended onto the septum.

The speed at which the excitatory process spreads through a certain segment of the myocardial syncytium depends upon the orientation of the fibers in that segment to each other and to the point of origin of excitation. Spread down a strip of fibers of which the long axis is parallel to the long axis of the strip is rapid as compared with spread down a strip in which the fibers run at a right angle to the long axis of the strip. Endocardial activation is rapid, not because of the presence of Purkinje fibers, but because the subendocardial bands of myocardium form a network through which excitation can move rapidly along the long axis of the fibers. Spread across the septum in bundle-branch block and across the free wall of the left ventricle in the normally activated heart is slow because excitation is moving through fibers the long axis of which is prependicular to the advancing wave of excitation.

Two cases of mitral insufficiency are reported. In 1 case the lesion was produced by rupture of the chordae tendineae of the posterior leaflet of the mitral valve. In the other case it was produced by fibrous adhesion of the posterior leaflet of the mitral valve to the underlying left ventricular wall, which occurred during healing of subacute bacterial endocarditis. Changes occurred in the pulmonary vascular bed which are essentially identical with those found in mitral stenosis.

Persistent pericardial effusion in the absence of obvious preceding or concurrent disease presents a baffling problem. In such cases chylopericardium, cholesterol pericarditis, lupus erythematosus, malignant disease, myxedema, severe anemia, and scleroderma, must be considered. Six cases are reported with large effusions present for from 1 to 11 years. The diagnostic measures to be used, the results of histologic examination, and the effects of surgery on the clinical course are discussed.

The present studies are concerned with the effect of high oxygen inhalation on patients with atrial septal defects. The problem of the amount of pulmonary vascular resistance and the relative contribution of irreversible structural changes and vascular tone may be of important prognostic significance in evaluation of such patients for cardiac surgery.

The relative importance of organic changes and vasoconstrictive influences in the production of increased pulmonary vascular resistance in congenital heart disease is problematic. With use of a grading system previously described, a study was made of the relation between each of the grades of hypertensive pulmonary vascular disease associated with ventricular or atrial septal defects and the change of pulmonary artery blood pressure immediately following closure of the abnormal communications. The immediate reversibility of the pulmonary hypertension varies inversely with the severity of the structural changes.

This series of papers constituted the second Symposium on Cardiovascular Sound conducted in association with the Scientific Sessions of the American Heart Association. The symposium took place on Friday, October 25, 1957, at the Hotel Sherman in Chicago. The chairman of the morning sessions was Dr. Hans H. Hecht of Salt Lake City; Dr. J. Willis Hurst of Atlanta was chairman for the afternoon sessions. The first symposium was published in Circulation 16 : 270, and 414, 1957. This publication was made possible by a grant-in-aid front the National Heart Institute, U.S. Public Health Service, and by contributions from Mr. Arthur L. Humphries, The Rena and Walter Burke Foundation, Lakeside Laboratories, Burroughs-Welcome Company, and the Wyeth Laboratories.

The medical problems in the selection of patients for direct-vision reconstructive operations utilizing the pump-oxygenator of the Gibbon type are discussed. The evaluation of the pulmonary vascular changes is one of the most important medical tasks in many cases. The operative risk for such lesions as ventricular septal defect with high pulmonary flow, tetralogy of Fallot, pulmonary stenosis with intact ventricular septum, and atrial septal defect of the partial atrioventricular canal type is constantly decreasing and is 15 per cent or less at the present time. Heart block and cardiac arrhythmias are still, on occasion, serious postoperative complications. During 1 period of 3 months, subacute bacterial endocarditis ( Pseudomonas ) occurred in 4 patients but it has not recurred since.

In a limited number of subjects having hypoxemia related to congenital malformations of the heart, no evidence was obtained of a correlation between the degree of hypoxemia or the extent of the polycythemia and the systemic blood flow. The circulatory response to exercise was characterized by a greater increase in the arteriovenous oxygen difference than in the systemic blood flow. A syncopal reaction in one patient was preceded by a greatly increased systemic blood flow and a small arteriovenous oxygen difference.