Negative P Waves in Lead I in Dextroversion: Differential Diagnosis from Mirror-Image Dextrocardia

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Abstract
The electrocardiographic differentiation of dextroversion from mirror-image dextrocardia has frequently been based on the configuration of the P waves in lead I, the assumption being that P waves are upright in dextroversion and inverted in mirror-image dextrocardia. A patient is presented with inverted P waves in lead I in whom an electrocardiographic diagnosis of dextroversion was made based on the analysis of the unipolar leads. This diagnosis was confirmed at surgery when a ventricular septal defect was successfully repaired. The Sodi-Pallares method of analysis of the precordial leads is valuable in determining whether the left ventricle lies anteriorly and to the left as in dextroversion or posteriorly and to the right as in mirror-image dextrocardia. Because of the frequency of unusual atrial rhythms in patients with right-lying hearts, the configuration of the P waves is often unreliable. When there is a discrepancy between the result of analysis of atrial activation and that of ventricular activation, the latter should be used in determining whether dextroversion or mirror-image dextrocardia is present.