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Diagnosis:
a) Lateral wall infarction
b) Dextrocardia
c) Arm lead inversion
d) None of the above
Answer: c) Arm lead inversion
Arm lead inversion (right arm lead placed on left arm and vice versa) can be recognized by inverted P waves, negative QRS and T waves in lead I. The same pattern can be seen in true dextrocardia as well. But in true dextrocardia, the chest electrodes will not show the usual progression of R waves, instead the QRS amplitude will progressively decrease from V1 to V6 as the heart is on the opposite side. Simple option is to get a repeat ECG for verification, if possible under direct supervision. Arm lead inversion or technical dextrocardia is one of the commonest errors in ECG recording.
This ECG also shows narrow Q waves and prominent T waves in lateral leads with mild concave upwards ST segment elevation. The S waves in lead V1 is deep and the R waves in V6 are tall, possibly an evidence of left ventricular hypertrophy by voltage criteria.