Biphasic P Waves–Paying Attention to Details| Biomed Grid

On a rather usual electrocardiogram (ECG) a rather unusual morphology of the P waves provided the chance for my young colleagues and me, the veteran, to sharpen some of our professional skills. The Case: The patient, a 69-year-old man, was transferred for rehabilitation in the following of mitral and aortic valve replacement. The ECG on admission showed sinus rhythm, 98 bpm, and left ventricular strain (Figure 1). On closer inspection (Figure 2), the P wave duration 140 msec is consistent with intra-atrial conduction delay, i.e. inter-atrial block. The P waves are biphasic in the limb leads. The first component of the P waves is positive in leads II, III and aVF, that means that the vector is directed downward toward the atrioventricular node. The late component of the P wave is opposed to the first, engraving a negative spike in leads III and aVF and a positive spike in lead aVL. This late P vector moves away from the atrio-ventricular node and upward to the farer areas of the left atrium. The 150 msec normal PR interval shows that arrival of the depolarization vector to the ventricles is not late. The questions are: where in the atrial walls is the site of the delay and what is the explanation for the to-and-fro atrial depolarization?