By Ken Grauer, MD
Professor Emeritus in Family Medicine, College of Medicine, University of Florida
The ECG in the figure below was obtained from an older man with new chest pain. There are two principal ECG findings on this tracing. Do you see both?
This is an extremely challenging ECG to interpret. The tendency is to allow your eye to jump to the most abnormal findings, which are the ST elevation with T wave peaking in each inferior lead (II, III, and aVF) and the symmetric T wave inversion in leads aVL, V1, and V2. But even before you see lead II, there is something wrong with the appearance of lead I.
You will virtually never normally see global negativity (i.e., of P wave, QRS complex, and T wave) in lead I. If you do, suspect some form of lead misplacement. The most common form of lead misplacement is to mistakenly interchange the left arm (LA) and right arm (RA) electrodes. When this happens, lead I becomes inverted, leads II and III switch places, and leads aVL and aVR switch places. Lead aVF and all the chest leads remain the same.
What makes this tracing challenging is that in addition to LA-RA lead reversal, there is ongoing acute infero-postero infarction, with acute ST-T wave changes in multiple leads. This is why the ST segment in lead I is elevated instead of showing the T wave inversion that usually is seen when there is LA-RA lead reversal in an otherwise normal tracing.
Despite this ST elevation in lead I, the negative P wave and deep Q wave in lead I simply is not an expected finding in lead I. In addition, the normal upright P wave in lead II that we expect to see with sinus rhythm is not present in the tracing. Although it is possible the patient might be living with some sort of ectopic atrial rhythm, a much more common cause of the unusual QRST appearance in lead I and the lack of an upright P wave in lead II is limb lead reversal. The easy solution is to repeat the ECG after verifying accurate electrode lead placement.
Repeating the ECG confirmed LA-RA lead reversal. Cardiac catheterization revealed complete occlusion of the proximal right coronary artery. For more information about and further discussion of this case, please click here.
The ECG in the figure was obtained from an older man with new chest pain. There are two principal ECG findings on this tracing. Do you see both?
You have reached your article limit for the month. Subscribe now to access this article plus other member-only content.
- Award-winning Medical Content
- Latest Advances & Development in Medicine
- Unbiased Content