Paroxysmal Tachycardia

1.1. Multiple precordial leads were studied in 67 persons. Ten of these had normal hearts and the remainder were suffering with cardiac disease of various kinds. The recent recommendations of the American and the British Heart Associations for routine and multiple precordial leads were followed. Leads IV R, IV F and IV L were taken with the precordial electrode just outside the apex and the indifferent electrode on the right arm, left leg, and left arm, respectively. The galvanometer connections were made in such a way that relative positivity of the electrode nearer the heart was represented by an upward deflection (R-wave). The multiple leads, designated CR, CF, and CL, were taken with the precordial electrode in six different positions extending from the right sternal border to the left midaxillary line (C1, C2, C3, etc.). The normal Lead IV and its variations are discussed.2.2. In medial positions (near the sternum) the initial positive deflection (R-wave) tends to be small, and the following S-wave large. As the precordial electrode is moved laterally, the size of the R-wave tends to increase and that of the S-wave to decrease. In normal hearts this change in the QRS complexes is slight, but, when the heart is enlarged, the shift of the QRS is often striking, and may be quite sudden and marked with only a slight change in position of the precordial electrode. A complete change of the QRS complexes from abnormal in the medial positions to normal in the axillary positions was seen in several of the patients with diseased, enlarged hearts. This was especially evident in those who had previously had anterior myocardial infarcts. There was no relation of this shift to the electrical axis in the limb leads.3.3. The T-waves were usually most satisfactorily recorded with the exploring electrode near the usual apex area (5th intercostal space, left midclavicular line). The P-waves, in most instances, were largest when the electrode was placed in the medial positions, just to the left of the sternum.4.4. All waves tended to be of greater amplitude with Lead CR than with Lead CF or CL. The reasons for preferring Lead CR (and IV R) to Lead CF in cases of pericarditis are given.5.5. For routine work, when only one precordial lead is taken, we believe that Lead IV R (apex and right arm) is the one of choice, provided that the heart is not appreciably enlarged. With moderate or marked cardiac enlargement, it seems preferable to place the precordial electrode medial to the apex and never farther to the left than the anterior axillary line.