Pruitt, Raymond D.

Potential changes attending excitation of the atrioventricular node, the common bundle, the bundle branches, and initial ramifications of the conducting tissue in the subendocardium of the bovine heart beating in situ have been recorded from unipolar exploring electrodes. Correlations between the form of nodal deflection and the location in the node of the electrode tip have been established. From right bundle branch and subendocardial action potentials, data were derived indicating a rate of transmission through the right branch of 2.02 M/sec. Certain observations on the effects of acute injury and severe hypoxia are recorded. The character of nodal deflections attending retrograde excitation is reviewed. In studies on canine hearts beating in situ , electrograms have been made from the regions in which the atrioventricular node, the common bundle, and bundle branches are believed to lie. Deflections comparable to those recorded in bovine experiments were encountered and, by analogy with those bovine studies, certain morphologic correlations postulated. In general, canine nodal deflections are smaller than their bovine counterparts and lack the variety of form ascribed to potential changes in the several portions of the bovine node. In canine studies, deflections of atrial, atrionodal, and nodal type coexisted in recordings from a single needle electrode suggesting a degree of proximity between the sources of these potential changes not encountered in bovine experiments.

A simple classification of atrioventricular block, criteria for diagnosis, and suggested therapy are discussed. The differences between Mobitz I and II second-degree A-V block are reviewed. Good management of patients who have bundle-branch or other forms of intraventricular block depends on informed judgment which includes consideration of (1) the effect of intraventricular conduction disturbances on the pumping action of the heart, and (2) the likelihood that a specific intraventricular conduction disturbance will be complicated by complete heart block. Evidence suggests that common forms of intraventricular disturbance, unlike ventricular fibrillation, do not alter significantly the pumping action of the heart. The role of intraventricular conduction disturbances in the genesis of ventricular fibrillation is assessed. We concluded that only when right bundle-branch block is combined with block of the anterior or posterior fascicle of the left bundle branch is complete heart block sufficiently imminent to warrant special concern. If bilateral block is associated with symptoms of episodic severe bradycardia, pacemaker therapy is indicated.

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.

Among 24 cases of small subendocardial infarctions included in this report are 10 cases of anteroseptal distribution in which the electrocardiogram was characterized by the presence of deeply inverted T waves in some or all of the precordial leads. Two other types of change encountered among the remaining 14 cases are described. Electrocardiographic changes in this group of 24 cases are compared with changes encountered in 5 cases of large and near circumferential acute subendocardial infarction described in part I of this study.

The electrocardiographic consequences of subendocardial infarction will find their most evident and characteristic expression in the acute has of a large lesion. Five cases of this kind are presented here and the associated electrocardiographic changes are described. At what level in the myocardium between the endocardium and epicardium do the electrocardiographic expressions of subendocardial infarction give way to those of transmural infarction Data in 6 cases of large nontransmural infarction are presented for comparison with findings in the 5 cases of subendocardial infarction.

This conference has been concerned with a case of primary systemic amyloidosis in which death occurred in the course of severe, congestive heart failure. Major emphasis has been attached to the diagnostic problems which were posed by a patient so afflicted. If comments regarding treatment have been of limited extent, so have been the results of treatment when applied.