What does "rSR'" in V1 or V2 indicate?

The presence of "rSR'" in leads V1 or V2 on an electrocardiogram (EKG) typically indicates a right bundle branch block (RBBB). This pattern is characterized by an initial R wave (r) followed by a small downward deflection (S) and then a subsequent R wave (R') returning toward the baseline. This occurs because the electrical impulse takes longer to travel through the right bundle branch due to a block, causing a delay in ventricular depolarization.

In a right bundle branch block pattern, this rSR' configuration is most commonly observed in the right precordial leads, such as V1 and V2, and signifies that the electrical impulse is not traveling efficiently through the right side of the heart. It's important to understand that this finding helps differentiate RBBB from other conditions such as left bundle branch block, which would have a different morphology on the EKG.

Overall, recognizing the rSR' pattern is crucial for healthcare professionals when interpreting EKGs, as it provides insight into the conduction status of the heart.