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By Ken Grauer, MD
Clinical Scenario: The ECG shown in the Figure was obtained from a previously healthy 63-year-old woman with atypical chest pain. The answer to the question we raise in the title of this ECG Review (is there lateral infarction?) is no and possibly yes! Can you explain?
Interpretation: There are several unusual findings on this tracing. The first of these becomes evident when assessing the rhythm: P waves are not upright in lead II. Although atrial activity is not readily discernible in lead I, the negative QRS complex and T wave in this lead—in association with the upright QRS complex in right-sided lead aVR (a lead which should normally show complete negativity) strongly suggest either dextrocardia or lead misplacement as the cause of the unusual pattern. Normal R wave progression in the precordial leads rules out the former (since dextrocardia would result in reverse R wave progression). Confirmation of lead misplacement as the cause of this pattern is easily forthcoming by repeating the ECG after verifying that all limb leads are correctly placed. The deep Q waves (QS complexes) in leads I, II, and aVL disappeared, and a normal upright P wave was seen in lead II on repeat ECG.
Precordial leads are unaffected by limb lead misplacement. Thus, the worrisome ST segment sagging depression that is present in leads V4 through V6 of the Figure was unchanged on repeat ECG, suggesting a possible acute coronary syndrome. There is, therefore, no evidence of lateral infarction from inspection of leads I and aVL (because lead misplacement negates the meaning of the findings in these leads)—but ST depression consistent with possible acute infarction is present in the lateral precordial leads.