Case 137: A 68-Year-Old Man after Bypass Surgery
A 68-year-old man with severe angina underwent bypass surgery to the left anterior descending and circumflex arteries. The following ECG was recorded shortly after the operation, upon transfer to the ICU:
- Sinus bradycardia, 54/min
- Inferior infarct, age undetermined
The inferior infarction had been seen on previous ECG’s over the past year.
The following ECG was recorded at 4:01 AM on the day following surgery. The patient’s condition was stable. Of note, the previous signs of inferior infarction are no longer present – what is your explanation?
- Compared with the previous tracing, criteria for inferior infarct are no longer present
- Suspect lead placement error (left arm-left leg lead reversal)
When there are unexpected/unusual changes in the inferior leads, such as the sudden appearance or disappearance of an inferior infarct, the possibility of lead misplacement – particularly reversal of the left arm and left leg cables – should be considered, and if clinically indicated, a repeat ECG should be obtained.
In this case, the QRS pattern strongly suggests that aVL and aVF have been reversed. An interesting detail is that in this ECG, his P wave in lead II is smaller and “starts later” than in lead I. This is the reverse of what we expect,* and strengthens the suspicion that leads I and II have been reversed.
(*) Normally atrial depolarization starts in the superior region of the right atrium. The right atrial depolarization vector is directed inferiorly, perpendicular to lead I and directed toward lead II. For that reason, in lead II compared to lead I, the P waves usually appear to start earlier and are taller.
The possibility of a lead misplacement was recognized by the Intensive Care Unit staff, and the following ECG was recorded with correct lead placement. It is similar to the initial ECG, which confirms that the sudden disappearance of the signs of the previous inferior infarction had been due to a lead placement error.
Compare the correct and incorrect recordings. Notice that the reversal of the QRS pattern in the unipolar leads aVL and aVF is quite obvious. The Einthoven leads I and II are also reversed, but are less helpful.
ECG ID: E298