Changing P wave polarity. Intermittent posterior internodal conduction

Spontaneous changes of P-wave polarity without change in heart rate were noted on the resting electrocardiogram of a patient admitted because of chest pain. Intracardiac and His bundle electrograms were compatible with a sequence of activation from high to low right atrium with both positive and negative P waves in lead aVR. The decrease in the P-His interval with positive P waves in lead aVR is consistent with selective conduction via the posterior internodal pathway.