Inversion of the P Wave in the Third Lead of Electrocardiograms with a Large Q-3 Wave

In the course of a study of electrocardiograms which show a large Q-3 deflection, we noted what appeared to be a relative frequency of inversion of the P deflection in the third lead of these tracings. This appeared to be consistent with the finding of Carr, Hamilton and Palmer 1 that inversion of P-3 is occasionally associated with the production of a large Q-3 wave in electrocardiograms taken from pregnant women.

We undertook to determine the frequency with which an inverted P-3 wave is found in an indifferent series of electrocardiographic tracings and in a series of electrocardiograms which contain a large Q-3 wave.

No attempt was made in this study to exclude or separate electrocardiograms showing auricular fibrillation, auricular flutter, paroxysmal auricular tachycardia or nodal rhythm. In tracings where extrasystoles were present these were ignored—the P-waves associated with the normal sinus rhythm alone were examined. No attention was paid to diphasic P-waves or to isoelectric P-intervals. Only when the P-wave was wholly inverted was it included in this study. The large Q-3 waves were selected in accordance with Pardee's criteria 2 : 1—the Q was at least 25% as large as the largest deflection of Q-R-S; 2—there was no S-wave; 3—waves of the M and W types were omitted.

Analysis of 2500 consecutive electrocardiograms taken at the Jewish Hospital of Brooklyn revealed 73 with an inverted P-3 wave (3%); one with an inverted P-1 wave (0.04%); and one with an inverted P-2 wave (0.04%). Of the group of 73 with an inverted P-3 wave, 50 (68%) showed deviation of the ventricular electrical axis to the left; 20 (27%) showed normal direction of the ventricular electrical axis, and 3 (5%) showed deviation of the ventricular electrical axis to the right. Eight of the group of 73 showed a large Q-3 wave. The single record with an inverted P-1 showed deviation of the ventricular electrical axis to the left. The single record with an inverted P-2 showed inversion of P-3 as well, and a normal direction of the ventricular electrical axis.