Abstract
When an electrode at a distance from the heart is paired with an exploring electrode in contact with the ventricular surface, the curve obtained represents the potential variations of the latter. By comparison the potential variations of the former are so small that they may be neglected. The curve obtained from a given point when the ventricular surface upon which the exploring electrode is placed is exposed to the air is larger but similar in all other respects to that obtained from the same point when the heart is completely surrounded by a conducting medium. When the muscle beneath the exploring electrode is injured, pronounced displacement of the RS-T segment occurs and the ventricular complex often becomes monophasic. If the connections have been made so that relative negativity of the exploring electrode produces an upward deflection, the direction of this displacement is downward. When the subepicardial muscle is injured over a large area and the injury and the exploring electrode are on opposite sides of the heart, the displacement is upward and is less pronounced. At the time when the displacement is maximal the electric field about the heart is similar to the one that would be produced if the surface between the injured and the uninjured muscle were polarized in such a sense as to make the injured muscle positive. A local injury on the epicardial surface does not alter the action current produced by portions of the heart that the injury does not involve. In any lead the deflections that are written before the excitation wave reaches the injured region are of the same form after the injury as before. The RS-T displacement produced by burning the surface of the cold-blooded heart quickly subsides and is not, apparently, followed by T-wave changes of the kind that occur when the mammalian heart is injured by coronary ligation.
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