ECG Review-A Lead Switch?
The ECG shown in the Figure was obtained from a 60-year-old woman. Is it likely that the leads were reversed?
Interpretation: The rhythm appears to be sinus at a rate of about 75 beats/minute. The most remarkable finding on this tracing is the negative P wave and almost complete negativity of the QRS complex in lead I that occurs in association with a predominantly positive QRS complex in lead aVR. Normally, the P wave and QRS complex are both upright in lead I and negative in right-sided lead aVR, reflecting the predominant direction of ventricular activation toward the left side of the chest. By far, the most common cause of the findings shown in leads I and aVR of this tracing is lead reversal, specifically mixing up the left and right arm electrodes. That said, this is not the cause of these findings in this tracing. Note the complete lack of R wave progression in the precordial leads of this ECG. Regardless of limb lead misplacement, if the heart were contained within the left side of the thorax, one would expect normal R wave progression with increasing QRS amplitude in the lateral precordial leads. The reason for reverse R wave progression and QRS negativity in lead I of this ECG is that the patient has dextrocardia.