In incomplete right bundle branch block, the QRS interval is widened, but is insufficiently prolonged to meet the criteria for right bundle branch block.

• Incomplete RBBB is defined by QRS duration between 110 and 120 ms in adults, between 90 and 100 ms in children between 4 and 16 years of age, and between 86 and 90 ms in children less than 8 years of age.
• Other criteria are the same as for complete RBBB.
• In children, incomplete RBBB may be diagnosed when the terminal rightward deflection is less than 40 ms but greater than or equal to 20 ms.
• The ECG pattern of incomplete RBBB may be present in the absence of heart disease, particularly when the V1 lead is recorded higher than or to the right of normal position and r′ is less than 20 ms.
• The terms rsr′ and normal rsr′ are not recommended to describe such patterns, because their meaning can be variously interpreted. In children, an rsr′ pattern in V1 and V2 with a normal QRS duration is a normal variant.