An Internal Electrocardiographic Lead.

The increased interest in chest and precordial leads, which are semi-direct leads tapping the cardiac action current from points close to the anterior surface of the heart, prompted the authors to seek an equivalent lead portraying more intimately the electrical phenomena at the posterior surface and base of the heart. A lead taken from the back of the chest fails to do this, for unlike the front, where there is only 1/2 inch of tissue intervening between heart and electrode, there is usually 4 inches of intervening tissue posteriorly. The difficulty was overcome by making use of the fact that the esophagus is closely attached to the posterior pericardium throughout its extent. A non-polarizable German Silver electrode, shaped somewhat like the Rehfuss tip, to which a thin flexible German Silver cable was clamped, served as an internal electrode. The cable was insulated throughout its length by rubber tubing. This electrode was swallowed in turn by 6 normal subjects, very much like the Rehfuss tube, its descent being checked by fluoroscopic examination. The esophageal electrode was connected to the right-arm side of the galvanometer, and the left-arm electrode (a flat 1 inch disc) lead to some point distant from the heart, such as the left leg or right arm of the subject. When the internal or exploring electrode lay at the level of the auricles, the electrocardiogram demonstrated uniformly a peculiar deflection, a very sharp, steep, rapidly moving deflection, which arose from the rounded portion of the P-wave, and which was almost as tall as the QRS deflection, which it resembled. (See Fig. 1.)