By Ken Grauer, MD
Professor Emeritus in Family Medicine, College of Medicine, University of Florida
Dr. Grauer reports no financial relationships relevant to this field of study.
The ECG in the figure below was obtained from a middle-age woman who presented with new dyspnea. Is the T wave inversion in the inferior leads a reflection of right ventricular “strain” from acute pulmonary embolism? If not, what else might cause these ECG findings?
As always, the interpretation should be systematic, beginning with an assessment of the cardiac rhythm. Notice that the P wave in lead II is negative. This means there could be a low atrial or junctional rhythm, there is dextrocardia, or there is some type of lead misplacement. This is because the P wave in lead II always should be upright when the rhythm is sinus, unless there is dextrocardia or lead misplacement. One can quickly rule out dextrocardia in this patient because R wave progression is normal (i.e., the R wave becomes predominantly positive — if not in lead V3, then definitely by lead V4, which is normal).
Several clues suggest that rather than a low atrial or junctional rhythm, the problem is some type of lead misplacement. In addition to the finding of a negative P wave in lead II, lead aVR does not show global negativity (i.e., a negative P wave, QRS complex, and T wave). Instead, lead aVR shows a significantly positive R wave (considering how reduced QRS amplitude is in this lead). The QRS complex and the ST-T wave in each inferior lead looks strikingly similar. Although none of these ECG findings alone is diagnostic of lead misplacement, the combination of the three factors should make this consideration high on the list of possibilities. The most common type of lead reversal is mixing up the left arm (LA) and right arm (RA) electrodes. When this happens, the P wave may become negative in lead II despite a sinus rhythm, there is global negativity (of P wave, QRS complex, and T wave) in lead I, and there is no longer global negativity in lead aVR. The positive P wave, QRS complex, and T wave in lead I in the figure rules out the possibility of LA-RA reversal. As a result, suspect some other type of lead reversal.
Recognizing the specific type of lead reversal is not important. What counts is recognizing that QRST morphology in several leads is highly unusual, and possibly (if not almost certainly in this case) the result of some type of lead misplacement. All the clinician needs to do at this point is repeat the ECG after verifying lead placement. Unfortunately, lead misplacement was not recognized in this patient. That said, one may strongly suspect there was RA-left leg lead reversal, which, when corrected, would have produced a normal ECG.
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