Electrical Effects of Stimulating the Endocardial Surface of the Right Ventricle of the Dog

Abstract

The endocardial surface of the right ventricle in four dogs was stimulated by a unipolar electrode introduced into the cavity of the right ventricle by means of a catheter. Electrical changes at a suprajacent point on the right wall were recorded by the V lead method of Wilson. In every experiment the induced QRS complexes were initiated by a positive electrical change.T HERE is considerable difference of opinion regarding the polarity of the initial electrical change recorded from a point on the thoracic w all when the endocardial surface of the subjacent ventricular wall is stimulated. Lewis and Rothschild' 2 reported that for the free wall of the right ventricle the initial change in potential, relative to a point transversely across the thorax is positive, whereas an initially negative deflection appears when the epicardial surface is stimulated. On the other hand, Nahum and Hoff3 4report that both endocardial and epicardial stimulation produce the same effect, namely, an initially negative deflection at a suprajacent point on the thoracic wall. Of course the thorax, previously opened, had been closed, and the lungs inflated, when the stimuli were applied. Hoff's view is that the endocardial response may contribute to electrical changes, but that the sign of the electrical effect is the same, whether endocardium or epicardium is first stimulated.5In a previous paper, reasons were given for doubting the adequacy of the method employed. The gests slower. electrical recovery of the endocardial than of the epicardial muscle surface, and this indicates that the inner surface has a longer refractory period.For these reasons, we decided to stimulate the endocardial surface of the right ventricle by means of a wire passed through a catheter, the end of which, after the catheter was passed through the jugular vein, was in contact with the inner surface of the free wall of the right ventricle. The tip of the wire was rounded to prevent injury by attaching a small globule of soldering metal to it. The stimulus was unipolar, being delivered from the secondary of an inductorium. The indifferent electrode was a metal plate placed at a distance on the dog's body. The stimulus strength was adjusted so that responses were obtained on the break, but not on the make. This precluded too strong stimulation. Before stimulating, the right vagus was faradized, this being continued for several seconds while the stimuli were being applied to the ventricle. Arresting the heart by vagus stimulation accomplished two things: it assured complete recovery of the muscle from refractoriness before the shock was applied, and it permitted the tip of the catheter and wire to come to rest in contact with ventricular wall. Fluoroscopic examination was used to place the catheter, and a roentgenogram was taken to show the positions of stimulating and recording electrodes. Furthermore, the location of the tip of the catheter was confirmed at autopsy. No The precordial electrode was placed on the right precordium suprajacent to the part of the ri...