Digging Deeper for the Differential Diagnosis of Negative P Waves in Lead I

To the Editor We read with great interest the report by Drs Chang and Jin¹ on a case of mirror-image dextrocardia with right bundle-branch block. Results of the patient’s electrocardiogram (ECG) revealed an abnormal P-wave axis in leads I and aVL (the polarities of P waves, QRS complexes, and T waves were all negative in lead I and aVL) and aVR (positive P waves). An abnormal QRS axis was also noted in leads I, aVL (negative), and aVR (positive QRS), with a progressively smaller left-sided precordial QRS voltage suggesting that the electrodes were moving farther away from a right-sided heart and that the patient had dextrocardia.