Identification of the Right Bundle Branch Block

Blocks are often a topic of confusion for 12 lead ECG enthusiasts. When screening for the presence of a right bundle branch block (RBBB), it is imperative to first obtain a full 12 lead. The presence of "notching" or "rabbit ears" on the rhythm strip alone is insufficient for diagnosis.

DIAGNOSIS
First, examine lead V1. A supraventricular rhythm must be present. Next, determine the duration of the QRS complex. A complete block is present if the QRS duration exceeds 0.10 seconds. RBBB typically presents as an UPRIGHT complex in lead V1. In addition, there complex contains a terminal R wave. The T wave is also negatively deflected in lead V1. "Slurred" S waves are typically identified in leads 1 and V6.

SIGNIFICANCE
RBBB is typically NOT an ischemic finding. Its prevalence increases with patient age. In the setting of tachycardia and other abnormal vital signs, however, RBBB can indicate right heart strain. A large pulmonary embolism, for example, can cause right heart strain and manifest as tachycardia, RBBB, and right axis deviation. RBBB can be seen in health individuals. RBBB can also occur in the setting of chronic obstructive pulmonary disease and coronary artery disease.

PHYSIOLOGY
RBBB is caused when impulses do not travel to the ventricules by way of the right bundle. The "blocked" impulses cause a delay in right ventricular depolarization. Because conduction through the purkinje fibers is slower than through the right bundle, the QRS complex increases in duration. Simply put, the ventricles no longer receive simultaneous electrical impulses.

12 Lead ECG of Right Bundle Branch Block