The Lewis lead describe a different positioning of the limb leads in order to better visualize atrial activity.
The Lewis lead can help better visualize atrial activity. Lead placement is demonstrated here. RA, right arm electrode; LA, left arm electrode; LL, left lower limb electrode; RL, right lower limb electrode.
Lewis lead unmasking atrial tachycardia with 2:1 conduction. Lead I demonstrates clear atrial activity.
Bakker ALM, Nijkerk G, Groenemeijer BE, et al. The lewis lead: Making recognition of p waves easy during wide QRS complex tachycardia. Circulation. 2009;119(24). doi:10.1161/CIRCULATIONAHA.109.852053