The R wave is the first upward deflection after the P wave and part of the QRS complex. The R wave morphology itself is not of great clinical importance but can vary at times.
The R wave should be small in lead V1. Throughout the precordial leads (V1-V6), the R wave becomes larger — to the point that the R wave is larger than the S wave in lead V4. The S wave then becomes quite small in lead V6; this is called “normal R wave progression.” When the R wave remains small in leads V3 to V4 — that is, smaller than the S wave — the term “poor R wave progression” is used.
Both types of wave progression are depicted below.
Recall that the R wave is usually quite small in lead V1; if the R wave is large in V1 — that is, greater in amplitude than the S wave — significant pathology may be present.
The causes for a R/S wave ratio greater than 1 in lead V1 include right bundle branch block, Wolff-Parkinson-White syndrome, an acute posterior myocardial infarction, right ventricular hypertrophy and isolated posterior wall hypertrophy, which can occur in Duchenne muscular dystrophy.
If a right bundle branch block is present, there may be two R waves, resulting in the classic “bunny ear” appearance of the QRS complex. In this setting, the second R wave is termed “R’” or “R prime.”