Identification of P waves after the Cox-maze procedure: significance of right precordial leads V3R through V6R

Background. The maze circuit lengthens the period of atrial depolarization and may lead to small or absent P waves, which may not be readily apparent in a standard 12-lead electrocardiogram. In this prospective study, we investigate if the right precordial leads V3R through V6R can improve detection of P waves and identification of atrial electrical activity. Methods. Standard 12-lead electrocardiograms (with leads I through III, aVR, aVL, aVF, and V1 through V6) and right precordial electrocardiograms (V3R through V6R) were recorded in 30 consecutive patients during the first 5 postoperative days and 1, 3, 6, 12, and 24 months after combined Cox-maze III procedure and mitral valve surgery. The P wave identification as an indication of atrial electrical activity and atrial contraction was proved by transesophageal echocardiographic identification of atrial contractions. Results. Despite echocardiographically identifiable atrial contractions, the P waves were not visible on standard 12-lead electrocardiograms in 7 (23%) patients after 1 and 3 months, and in 4 patients after 6 months. In contrast, right precordial electrocardiograms showed P waves in all of these patients that were best seen in lead V4R. Twelve and 24 months postoperatively, only 2 patients had no visible P waves in the standard leads that were still present in the right precordial leads. However, if P waves were easily identifiable in standard 12-lead electrocardiograms (23 patients at 1 and 3 months after surgery), the right precordial leads showed P waves only in 15 patients. Conclusions. Right precordial electrocardiogram with leads V3R through V6R is a helpful tool for visualizing P waves after the Cox-maze procedure. Standard 12-lead electrocardiogram should be combined with right precordial electrocardiogram in all patients after the Cox-maze procedure.