Comparison of P waves recorded on the standard electrocardiogram, the "Lewis lead," and "saline-filled central venous catheter"-based intracardiac electrocardiogram

The feasibility of recording the intracardiac electrocardiogram (IC-ECG) through a saline-filled central venous catheter has been demonstrated. The importance of identifying P waves for the accurate characterization of arrhythmias has long been emphasized. The "Lewis lead" has been occasionally employed when the standard electrocardiogram (SECG) fails to detect P waves. The objectives of this study were to compare the amplitude of P waves recorded by intracardiac and standard ECGs and the Lewis lead and to explore whether the latter has any advantages over either type of electrocardiography. The amplitudes of P wave (in millimeters) measured on SECG, the Lewis lead, and IC-ECG obtained through a saline-filled central venous catheter were compared; recordings were obtained through the intracardiac electrocardiographic distal, medial, and proximal ports of the central venous catheter in 28 patients who underwent 62 measurements. P waves were larger on the distal port of the IC-ECG than on the medial and proximal ports, on lead V₁, the lead with the tallest P wave on SECG, and the Lewis lead (all p = 0.0005). P waves were also larger on the medial port than on the proximal port of the IC-ECG (p = 0.0005). P waves were larger on the proximal port of the IC-ECG than on lead V ₁, the lead with the tallest P wave on SECG, and the Lewis lead (p = 0.0005 for the 2 leads), and P waves were larger with the Lewis lead than on lead V₁ (p = 0.0005) but did not differ from the lead with the tallest P wave on a SECG (p = 0.124). Augmented P waves can be secured by employment of an intracardiac electrocardiographic lead; the Lewis lead has no advantages over the SECG for detecting P waves. These data are useful when the amplitude of P waves is an issue of concern in clinical practice and research.