Prominent R wave in lead V1: electrocardiographic differential diagnosis.

Tall lead V1 (tall RV1), defined as an R/S ratio equal to or greater than 1, is not an infrequent occurrence in emergency department patients. This electrocardiographic finding exists as a normal variant in only 1% of patients. Physicians should therefore be familiar with the differential diagnosis for this important QRS configuration. The electrocardiographic entities which can present with this finding include right bundle branch block, left ventricular ectopy, right ventricular hypertrophy, acute right ventricular dilation (acute right heart strain), type a Wolff-Parkinson-White syndrome, posterior myocardial infarction, hypertrophic cardiomyopathy, progressive muscular dystrophy, dextrocardia, misplaced precordial leads, and normal variant. Various cases are presented to highlight the different causes of the tall RV1.