ECG Review-Confirming Dextrocardia: Technician Error

Clinical Scenario: The ECG shown in the Figure was obtained from a 60-year-old woman with dextrocardia (it is the follow-up tracing to the ECG shown in last month’s ECG Review). In an attempt to confirm the diagnosis of dextrocardia, the tech had been asked to "repeat the ECG with the leads reversed." How should the tech have been instructed to repeat this ECG? What simpler approach could have been used to confirm dextrocardia?

Interpretation: The finding of complete (or almost complete) negativity of the QRS complex in lead I in association with an upright QRS complex in lead aVR is distinctly abnormal and should always prompt consideration of two clinical entities: 1) dextrocardia; and 2) limb lead misplacement. Practically speaking, the latter is much more common. Assessment of R wave progression in the precordial leads will usually distinguish between these two entities: R wave progression should be normal when there is limb lead reversal, whereas R wave progression is reversed when there is dextrocardia (as it was in last month’s ECG Review). Verifying correct placement of limb lead electrodes and then repeating the ECG with precordial leads reversed should confirm what the true diagnosis is, in that R wave progression will normalize for a patient with dextrocardia when precordial leads are placed on the right side of the chest (as they do in the Figure). The error the tech made in this case was to also reverse the limb lead electrodes, which is why the QRS complex is now upright in lead I. The simplest way to confirm dextrocardia is to listen for heart sounds on the right side of the chest.