The 12 Leads of Christmas: Lead I

This article is the first in our latest series, The 12 Leads of Christmas, where each day we examine a new finding particular to an individual electrocardiographic lead.

The Lead I Sign

This patient has COPD.

Lead I Sign


So does this patient.

Lead I Sign


Also, this patient.

08 - 1031 - 66yo M - 02


How do I know that? Well, I met the patients and they told me, but there’s also a very specific (but not very common) sign of COPD present on both tracings: the “lead I sign.” This manifests as nearly isoelectric complexes in lead I with barely any visible P, QRS, or T-waves.

Often termed “Schamroth’s sign” or “Schamroth’s pattern,” it should not be confused with Schamroth’s window test for identifying clubbing of the fingers.

Schamroth Clubbing

Schamroth’s window test.1


Also known as the “isoelectric lead I sign,” as far as my research can tell it was first identified and termed the “lead I sign” in 1965 by N.O. Fowler et al. in a series of 15 patients with severe emphysema and cor pulmonale.² The term was popularized, however, by Dr. Leo Schamroth, cardiologist and Chief of Medicine at Baragwanath Hospital in South Africa, and likely bears his name thanks to the efforts of Dr. Bill Nelson through his use of the eponym.

Though there is mention of strict voltage criteria in the Fowler paper (isoelectric P-wave, total QRS < 1.5 mm, T-wave <0.5 mm), Dr. Schamroth himself never used those numbers and simply described his sign as: “absent or very low amplitude P, QRS, T wave complexes giving the appearance of a minimally disturbed baseline.”³

Here’s another example of the sign in a patient with severe COPD:

Lead I Sign

Lead I sign.


It is important to note that all three main complexes—the P, QRS, and T-wave—must be tiny in lead I for the sign to be positive. Here’s a case of a 33-year-old male with a small QRS in lead I but very visible T-wave. It would be easy to confuse this with the lead I sign but really this is a normal ECG for a tall, thin male.

Normal ECG

Normal ECG.


The main reason we see the lead I sign is that COPD can produce a rightward deviation of all three complexes, sometimes resulting a P, QRS, and T-axes all pointing right around 90 degrees. Since lead I is located at 0 degrees—perpendicular to all three of those vectors—it cannot “see” any of them very well and registers almost no deflection.

90-Degree Axis

The other key to utilizing the lead I sign is that you have to be aware of the company it keeps. If there are no other signs of pulmonary disease on the EKG (as in the case of the 33yo M above), then you probably shouldn’t cite the sign. On the other hand, if there are multiple stigmata of pulmonary disease and “cor pulmonale” on the ECG, then you’re on the right track.

In the case below the complexes in lead I might be just a little too large to strictly cite this as a case of Schamroth’s sign, but when you look at the rest of the ECG you’ll note there are huge P-waves as evidence of right atrial abnormality, true right axis deviation, and a tall terminal R-wave in V1. These all point to pulmonary hypertension and overload of the right side of the heart, giving us a bit more leeway in our use of the sign than the original rigid criteria would allow.

Lead I Sign

Borderline lead I sign in a patient with severe COPD.

I have to imagine that is how Dr. Schamroth would have wanted us to use the sign.


Further Reading


  1. Schamroth L. “Personal Experience.” S Afr Med J. 1976 Feb 28;50(9):297-300. [PDF]
  2. Fowler, NO, Daniels, C, Scott, RC, Faustino, BN, Gueron, M. The Electrocardiogram in cor pulmonale with and without emphysema. Am J Cardiol. 1965;16:500-505. [Abstract]
  3. Schamroth L. The 12 Lead Electrocardiogram. 18th ed. Oxford: Blackwell Scientific Publications; 1989.

I hope you’re enjoying our 12 Leads of Christmas series. You can check out the rest of the posts below (updated as new posts come out):

12 Leads of Christmas: Lead II
12 Leads of Christmas: Lead II
12 Leads of Christmas: aVR
12 Leads of Christmas: aVL
12 Leads of Christmas: aVF
12 Leads of Christmas: V1
12 Leads of Christmas: V2
12 Leads of Christmas: V3
12 Leads of Christmas: V4
12 Leads of Christmas: V5
12 Leads of Christmas: V6


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