What are the causes of tall R waves in V1?

In normal individuals there is only a small R wave (r) in V1 which is followed by a deep S wave, indicating left ventricular dominance. Tall R in V1 usually make us suspect right ventricular hypertrophy. But tall R in V1 can occur without heart disease due to misplaced chest leads, rightward shift of the heart (dextroversion) due to acquired or congenital causes and occasionally as a normal variant.

The conventional ‘true posterior’ wall myocardial infarction (lateral wall infarction) can cause tall R in V1, which is equivalent to deep Q waves in posterior leads, seen as a mirror image in anterior leads. Tall R waves in V1 may also occur in Duchenne muscular dystrophy and hypertrophic cardiomyopathy. Right bundle branch block and accessory pathways causing preexcitation of posterior or lateral walls can also manifest tall R waves in V1. In WPW syndrome, it is the anteriorly directed delta wave which appears as tall R wave.