Understanding Bundle Branch Block

• Bundle branch block (BBB) impairs the transmission of electrical impulses due to a block in one of the heart's bundle branches.
• Electrical signals are conducted to the ventricles by these branches, leading to their contraction.
• The block can manifest as right bundle branch block (RBBB) or left bundle branch block (LBBB).
• BBB has various causes, including heart disease, high blood pressure, and certain medications.
• In some instances, the cause of BBB remains unknown.

Right Bundle Branch Block (RBBB)

• RBBB occurs when the electrical impulse is blocked in the right bundle branch.
• The right ventricle depolarizes later than the left ventricle because of RBBB.
• An electrocardiogram (ECG) can detect RBBB by a widened QRS complex (greater than 0.12 seconds) and an RSR' pattern in the right precordial leads (V1 and V2).
• Especially in young, healthy individuals, RBBB may be a normal variant.
• Structural heart disease like pulmonary embolism, right ventricular hypertrophy, or congenital heart defects can be associated with RBBB.
• Pulmonary artery catheterization can cause transient RBBB.
• Isolated RBBB typically doesn't need specific treatment without structural heart disease.
• Management focuses on addressing the primary cardiac issue if RBBB is associated with underlying heart conditions.

Left Bundle Branch Block (LBBB)

• LBBB occurs when the electrical impulse is blocked in the left bundle branch.
• The left ventricle depolarizes later than the right ventricle because of LBBB.
• An ECG can detect LBBB by a widened QRS complex (greater than 0.12 seconds) and broad, notched R waves in the left precordial leads (V5 and V6).
• LBBB also presents with absent Q waves in leads I, V5, and V6, along with prolonged R wave peak time in the left precordial leads.
• LBBB is almost always associated with underlying heart disease, unlike RBBB.
• Ischemic heart disease, hypertension, cardiomyopathy, and valvular heart disease are common causes of LBBB.
• New LBBB in the setting of chest pain is considered a STEMI equivalent, requiring immediate evaluation for myocardial infarction and possible reperfusion therapy.
• Diagnosing myocardial infarction becomes difficult on ECG because LBBB alters the typical ST-segment and T-wave morphology.
• Cardiac resynchronization therapy (CRT) may benefit patients with heart failure and LBBB by improving cardiac function and reducing symptoms.
• Pacing leads are placed in both ventricles during CRT to coordinate their contraction.

Causes of Bundle Branch Block

• Myocardial infarction or angina can damage the bundle branches, leading to a block from ischemic heart disease.
• Chronic high blood pressure can cause structural changes in the heart that affect the conduction system from hypertension.
• Cardiomyopathy disrupts the normal electrical pathways.
• Aortic stenosis or mitral regurgitation can cause hypertrophy and fibrosis, affecting the bundle branches from valvular heart disease.
• Some congenital heart abnormalities can involve or affect the bundle branches.
• A blood clot in the pulmonary artery can cause acute right ventricular strain and RBBB from pulmonary embolism.
• Antiarrhythmics are an example of medications that can sometimes cause or exacerbate BBB.
• Age-related fibrosis and sclerosis can affect the conduction system from degenerative changes.
• Amyloidosis or sarcoidosis can infiltrate the heart and disrupt the normal electrical conduction from infiltrative diseases.

Diagnosis

• An electrocardiogram (ECG) is the primary diagnostic tool for identifying BBB.
• The ECG can show the characteristic QRS complex widening and specific patterns associated with RBBB or LBBB.
• Medical history and physical examination help to identify potential underlying causes or associated conditions.
• An echocardiogram assesses the structure and function of the heart, helping to identify underlying heart disease.
• Stress testing may be used to evaluate for ischemia, particularly in patients with LBBB.
• Cardiac MRI can provide detailed information about the heart structure and identify infiltrative or inflammatory processes.

Treatment

• Isolated RBBB typically does not require treatment unless associated with symptoms or underlying heart disease.
• Treatment focuses on managing the underlying cardiac issue for underlying heart conditions.
• Cardiac resynchronization therapy (CRT) can be used in patients with heart failure and LBBB to improve cardiac function.
• Pacemaker implantation may be necessary in cases of BBB associated with symptomatic bradycardia or high-degree AV block.
• If a medication is suspected to be contributing to BBB, adjusting or discontinuing the medication may be necessary through medication adjustment.
• Managing risk factors such as high blood pressure, high cholesterol, and smoking can help prevent further cardiac damage through lifestyle modifications.

Prognosis

• Isolated RBBB generally has a good prognosis, especially in the absence of structural heart disease.
• LBBB can be associated with a higher risk of adverse cardiovascular events, particularly if associated with underlying heart disease.
• Patients with BBB should be monitored for progression of heart disease and development of complications.
• Prognosis varies depending on the underlying cause and the presence of other cardiac conditions.
• Regular follow-up with a cardiologist is important for monitoring and managing BBB.

Considerations for Specific Populations

• Age-related degenerative changes can increase the risk of BBB in the elderly.
• RBBB can be seen in highly trained athletes and may not indicate underlying heart disease.
• LBBB is common in patients with heart failure and may be an indication for CRT.
• New LBBB in the setting of chest pain requires immediate evaluation for myocardial infarction in patients with acute myocardial infarction.