From the Guidelines
Right bundle branch block (RBBB) is a condition where the electrical conduction through the right bundle branch is delayed or completely blocked, resulting in asynchronous ventricular contraction and characteristic ECG changes. The pathophysiology of RBBB involves a delay or block in the electrical conduction through the right bundle branch, forcing the electrical impulse to travel through the left bundle branch and then spread to the right ventricle through the myocardium rather than the specialized conduction system 1. This abnormal conduction pathway causes the right ventricle to depolarize after the left ventricle, resulting in asynchronous ventricular contraction.
ECG Changes
On an ECG, RBBB is characterized by:
- A widened QRS complex (≥120 ms)
- A distinctive RSR' pattern (rabbit ear appearance) in the right precordial leads (V1-V3)
- Wide S waves in the lateral leads (I, aVL, V5-V6) The terminal portion of the QRS complex is directed rightward and anteriorly, reflecting the delayed right ventricular activation.
Clinical Significance
RBBB can occur in otherwise healthy individuals but may also indicate underlying cardiac disease such as myocardial infarction, pulmonary embolism, congenital heart disease, or cardiomyopathy 1. The clinical significance of RBBB depends on the presence of associated conditions, as isolated RBBB generally doesn't require specific treatment but warrants evaluation for underlying cardiac pathology.
Diagnosis and Evaluation
According to the 2018 ACC/AHA/HRS guideline, patients with RBBB or intraventricular conduction delay on ECG have an increased risk of left ventricular systolic dysfunction compared with those with completely normal ECGs 1. Echocardiography can identify various structural cardiac abnormalities underlying conduction disturbance, including cardiomyopathy, valvular heart disease, congenital anomalies, tumors, infections, infiltrative processes, immunologically mediated conditions, and diseases of the great vessels and pericardium. The presence of RBBB on ECG should prompt further evaluation, including echocardiography, to rule out underlying cardiac disease.
From the Research
Pathophysiology of Right Bundle Branch Block
The pathophysiology of Right Bundle Branch Block (RBBB) involves an interruption in the normal electrical activity of the His-Purkinje system, resulting in an altered sequence of activation in the heart 2. This alteration leads to a characteristic appearance on the electrocardiogram (ECG), which is often seen in clinical practice.
Effect on ECG
The ECG findings in RBBB include:
- A widened QRS complex
- Changes in the directional vectors of the R and S waves 2 These changes are a result of the delayed activation of the right ventricle, which occurs when the electrical impulse is blocked in the right bundle branch.
Types of Block
Studies have shown that RBBB can be divided into different types based on the location of the block within the right bundle branch 3. These types include:
- Proximal block: characterized by a prolonged time interval from mitral to tricuspid valve closure (MCTC)
- Peripheral block: characterized by a prolonged time interval from tricuspid valve closure to the maximum opening of the pulmonary valve (TCPO)
- Diffuse block: characterized by both MCTC and TCPO prolongation
- Non-specific block: without prolongation of either MCTC or TCPO The most common type of block is peripheral block, which accounts for approximately 80.5% of cases 3.
ECG Findings
The ECG findings in RBBB can vary depending on the type of block, but common features include:
- Prolonged QMC (time interval from the initial deflection of the QRS complex to mitral valve closure)
- Prolonged QTC (time interval from the initial deflection of the QRS complex to tricuspid valve closure)
- Prolonged QPO (time interval from the initial deflection of the QRS complex to the point of full opening of the pulmonary valve) 3