Lead V1 is primarily used to identify a right bundle branch block (RBBB) because it is positioned at the right side of the chest, providing a view of the heart's electrical activity as it travels through the right bundle branch. In the case of RBBB, the impulse is delayed in reaching the right ventricle, leading to characteristic changes in the QRS morphology in lead V1.
When RBBB occurs, the ECG typically shows a "rabbit ears" pattern, or a wide, notched R wave, in lead V1. This abnormality is due to the delayed activation of the right ventricle compared to the left. The distinct changes observed in lead V1 are crucial for diagnosing RBBB, making it the key lead for this purpose. Other leads may also provide helpful information regarding overall cardiac function or conditions, but lead V1 is the most definitive for identifying this specific anomaly.