Lewis Lead Parallax
The following was recorded from a 90 year-old Caucasian man with shortness of breath.
This is very suspicious for second degree block; bigeminal PACs or PJCs with compensatory pauses are also possibilities. There is poor visualization of atrial activity due to background noise and intrinsic low voltage. The 12-lead is referenced for the best lead to visualize:
V1 seems promising; a V1 rhythm strip is acquired:
Worse still. Next, the Lewis lead:
Now the diagnosis is transparent. Before resorting to the placement of Lewis electrodes, the voltage gain can be doubled and noise reduction strategies applied. These were not utilized here.
12-lead under Lewis electrode placement:
There is diminished QRS voltage, new inferior Q-waves and ST-segment abnormalities. This could easily be misinterpreted, but it is an artifact of the lead system.
Switching back to standard placement. Different electrodes were used at this time and the voltage is altered; the background noise has faded but the atria remain quiet:
This patient was ultimately found to be pancytopenic (WBCs 3.1, RBCs 1.17, Hem 4.8, Crit 13.0, Platelets 96, Neu 23, Lym 60, Monos 16) and was worked up for myelodysplastic syndrome. The electrocardiographic findings may be associated with the anemia; they may also be incidental.
Christopher Watford brought the Lewis lead to my attention; he has described its physiology and advantages extensively in his blog post, Highlighting Atrial Activity on an ECG: The S5 Lead, as well as via audio on the EMCrit Podcast with Scott Wiengart.
There are numerous alternative lead systems: Brughada leads, high and low precordial placements for visualizing poorly represented territories, systems designed to emphasize pacemaker activity, etc. Body surface mapping technologies (e.g. The 80-Lead Prime ECG) have also shown promise. Some of these lead systems are described on this site under EKG Resources.
Bakker, A., et al. (2009). The lewis lead: Making recognition of P waves easy during wide QRS tachycardia. Circulation, (2009), 119; e592-e593. [Free Full Text] doi: 10.1161/CIRCULATIONAHA.109.852053
Lewis T. (1931). Auricular fibrillation. Clinical Electrocardiography. 5th ed. London, UK: Shaw and Sons; 1931: 87–100.