Introduction
Bundle Branch Block refers to a disturbance in the electrical conduction system of the heart, specifically within the bundle branches that transmit impulses from the atrioventricular (AV) node to the ventricles. When conduction is blocked or delayed in one or more branches, the coordinated contraction of the ventricles is affected, resulting in characteristic changes on the electrocardiogram (ECG).
Epidemiology
The prevalence of BBB increases with age and is often encountered in adults, particularly those with underlying cardiovascular disease. Right Bundle Branch Block (RBBB) is more frequently observed than Left Bundle Branch Block (LBBB). While BBB may be asymptomatic and discovered incidentally, its presence can signal underlying cardiac pathology and influence management decisions.
Clinical Significance
BBB is clinically relevant because it may indicate structural heart disease, predispose to arrhythmias, and affect the interpretation of diagnostic tests. LBBB, in particular, can mask or mimic myocardial infarction on ECG, complicate the assessment of ventricular function, and is associated with poorer outcomes in certain populations.
Cardiac Conduction System and Pathophysiology of BBB
The cardiac conduction system is responsible for the orderly propagation of electrical impulses that initiate myocardial contraction. The system comprises the sinoatrial (SA) node, AV node, bundle of His, right and left bundle branches, and Purkinje fibres.
The bundle branches are bifurcations of the bundle of His, dividing into the right bundle branch (RBB) and left bundle branch (LBB). The LBB further subdivides into the anterior and posterior fascicles. Normal conduction ensures synchronous activation of both ventricles. In BBB, a block or delay within one or more branches results in asynchronous ventricular depolarisation, which manifests as widened QRS complexes and specific patterns on ECG.
Pathophysiologically, BBB may result from fibrosis, ischaemia, or structural disruption of the conduction pathways. The consequences depend on whether the block is complete or incomplete and which branch is affected.
Types of Bundle Branch Block
Right Bundle Branch Block (RBBB)
RBBB involves delayed or blocked conduction through the right bundle branch. As a result, the right ventricle is activated later than the left, producing a distinctive rSR’ pattern in lead V1 and broad S waves in leads I and V6 on ECG. RBBB may be benign or associated with conditions such as pulmonary embolism, congenital heart disease, or right ventricular hypertrophy.
Left Bundle Branch Block (LBBB)
LBBB is characterised by impaired conduction through the left bundle branch, with delayed activation of the left ventricle. ECG features include broad, notched or slurred R waves in leads I, V5, and V6, and deep S waves in V1 and V2. LBBB is more often associated with underlying cardiac pathology, including coronary artery disease, hypertension, and cardiomyopathy.
Fascicular Block
Fascicular blocks, also known as hemiblocks, refer to conduction disturbances in the anterior or posterior fascicles of the left bundle branch. Left anterior fascicular block (LAFB) and left posterior fascicular block (LPFB) alter the axis of ventricular depolarisation, resulting in characteristic ECG findings. Fascicular blocks may occur in isolation or in combination with RBBB (bifascicular block) or LBBB (trifascicular block).
Causes and Risk Factors
Congenital Causes
Congenital BBB is rare but may be seen in certain structural heart diseases, such as congenital heart block, ventricular septal defect, or corrected transposition of the great arteries. In these cases, abnormal development or positioning of the conduction system predisposes to bundle branch block.
Acquired Causes
Most cases of BBB are acquired and result from diseases that affect the heart’s conduction system. Major causes include:
- Ischaemic Heart Disease: Infarction or chronic ischaemia may damage the bundle branches.
- Hypertension: Chronic pressure overload leads to ventricular hypertrophy and fibrosis.
- Cardiomyopathy: Dilated, hypertrophic, or infiltrative cardiomyopathies can disrupt conduction pathways.
- Degenerative Disease: Age-related degeneration (Lenègre’s or Lev’s disease) is a common cause in older adults.
- Valvular Heart Disease: Especially aortic stenosis or regurgitation due to proximity to the conduction system.
- Pulmonary Embolism: Can cause acute RBBB due to right ventricular strain.
- Trauma or Cardiac Surgery: Direct injury to the conduction system during procedures.
- Infective or Inflammatory Conditions: Myocarditis, endocarditis, or rheumatic fever.
Comorbidities and Risk Factors
Additional risk factors include advanced age, diabetes mellitus, chronic kidney disease, and a family history of conduction system disease. Lifestyle factors such as smoking, excessive alcohol consumption, and poor control of cardiovascular risk factors may contribute indirectly.
Symptoms and Clinical Presentation
The clinical presentation of BBB varies depending on the type, degree of block, and underlying cardiac status. Many patients are asymptomatic, and BBB is detected incidentally on routine ECG. However, symptomatic presentation may include:
- Palpitations: Sensation of irregular or forceful heartbeat.
- Syncope or Presyncope: Especially if BBB is associated with bradyarrhythmias or higher-degree AV block.
- Dyspnoea: Shortness of breath, particularly in heart failure or pulmonary embolism.
- Chest Pain: May occur if underlying ischaemic heart disease is present.
- Fatigue: Due to reduced cardiac output in cases of severe conduction disturbance.
It is important to note that isolated BBB without structural heart disease rarely causes symptoms. Symptomatic patients should be evaluated for underlying cardiac pathology or progression to higher-grade conduction block.
Diagnostic Methods
Electrocardiogram (ECG)
ECG is the primary tool for diagnosing BBB. The following features are considered diagnostic:
- RBBB: QRS duration ≥ 120 ms, rSR’ in V1, broad S in I and V6.
- LBBB: QRS duration ≥ 120 ms, broad, notched R in I, V5, V6, deep S in V1, V2.
- Fascicular Block: Axis deviation, small Q in I and aVL (LAFB) or II, III, aVF (LPFB).
Imaging Studies
Echocardiography is utilised to assess structural heart disease, ventricular function, and valvular abnormalities. Cardiac MRI may be indicated to evaluate myocardial fibrosis or infiltrative disease. CT coronary angiography assists in the assessment of coronary artery disease, especially in patients with LBBB where exercise stress testing may be unreliable.
Electrophysiological Studies
In selected cases, invasive electrophysiological testing may be necessary to localise conduction block, assess for additional conduction defects, or guide device therapy.
Differential Diagnosis
The differential diagnosis includes other causes of wide QRS, such as ventricular ectopy, pre-excitation syndromes (e.g., Wolff-Parkinson-White syndrome), and non-specific intraventricular conduction delay. A comprehensive clinical and ECG evaluation is essential for accurate diagnosis.
Treatment Options
Medical Management
Isolated BBB without symptoms or underlying heart disease generally does not require specific treatment. Management is directed towards the underlying cause, if present:
- Ischaemic Heart Disease: Antiplatelet agents, statins, beta-blockers, ACE inhibitors.
- Heart Failure: Diuretics, ACE inhibitors, beta-blockers, aldosterone antagonists.
- Hypertension: Lifestyle modification, antihypertensive medications.
- Infective or Inflammatory Conditions: Appropriate antibiotics or immunosuppressive therapy.
Device Therapy
Device therapy may be indicated in patients with BBB and symptomatic bradyarrhythmias, advanced AV block, or heart failure with reduced ejection fraction:
- Permanent Pacemaker: For high-grade AV block or symptomatic bradycardia.
- Cardiac Resynchronisation Therapy (CRT): For patients with LBBB and heart failure (QRS ≥ 130 ms, LVEF ≤ 35%) to improve synchrony, symptoms, and survival.
Lifestyle Modifications
Lifestyle changes are essential for managing cardiovascular risk factors:
- Regular physical activity
- Balanced diet (low salt, low saturated fat, high fibre)
- Smoking cessation
- Moderation of alcohol intake
- Strict control of diabetes, hypertension, and dyslipidaemia
Prognosis and Complications
The prognosis of BBB depends on the type, underlying cardiac pathology, and presence of symptoms. Isolated RBBB in healthy individuals typically carries a benign prognosis. LBBB, particularly in the context of heart failure or ischaemic heart disease, is associated with increased morbidity and mortality.
Complications of BBB may include:
- Progression to Complete Heart Block: Especially in degenerative or ischaemic disease.
- Arrhythmias: Increased risk of ventricular tachyarrhythmias, sudden cardiac death in certain populations.
- Heart Failure: Due to dyssynchronous ventricular contraction, particularly with LBBB.
- Diagnostic Challenges: Difficulties in interpreting ECG, especially for myocardial infarction in LBBB.
Preventive Measures and Patient Education
Prevention
Preventive strategies focus on reducing cardiovascular risk and managing underlying conditions:
- Control of hypertension, diabetes, and dyslipidaemia
- Regular cardiovascular screening for at-risk populations
- Prompt treatment of acute cardiac events (e.g., myocardial infarction)
- Lifestyle modification as outlined above
- Management of comorbid conditions (chronic kidney disease, obesity)
Patient Education
Patient education is crucial for adherence to medical therapy, recognition of symptoms, and timely follow-up. Patients should be informed about:
- When to seek emergency care
- The nature of BBB and its implications
- Warning signs of progression (syncope, palpitations, chest pain)
- The importance of regular follow-up and monitoring
- Benefits of healthy lifestyle choices
Nursing Care of Patient with Bundle Branch Block (BBB)
Patient Education
- Condition Explanation: Educate the patient and family about BBB, its causes, symptoms, and possible complications.
- Warning Signs: Instruct the patient to report symptoms such as chest pain, fainting spells, or severe palpitations immediately.
- Lifestyle Modifications: Advise on healthy lifestyle habits, including a balanced diet, regular exercise (as tolerated), stress management, and avoidance of smoking and excessive alcohol.
- Medication Compliance: Emphasise the importance of adhering to prescribed medications and regular follow-ups.
Medication Administration
- Drug Administration: Administer prescribed medications such as antiarrhythmics, antihypertensives, or other cardiac drugs, observing for side effects.
- Monitoring Response: Assess the patient’s response to therapy and report any adverse reactions to the physician.
Prevention of Complications
- Monitor for Arrhythmias: Be vigilant for the development of more severe arrhythmias or signs of heart failure.
- Emergency Preparedness: Be prepared to initiate emergency interventions such as cardiopulmonary resuscitation (CPR) or defibrillation if required.
- Fluid Balance: Monitor intake and output to prevent fluid overload, especially in patients with compromised cardiac function.
Psychosocial Support
- Emotional Support: Address patient and family anxiety, clarify doubts, and provide reassurance regarding prognosis and treatment.
- Counselling: Arrange for counselling services if needed, especially if the patient experiences significant stress or lifestyle changes due to the diagnosis.
Coordination of Care
- Multidisciplinary Approach: Collaborate with cardiologists, dieticians, physiotherapists, and other members of the healthcare team for comprehensive care.
- Follow-Up: Ensure timely follow-up appointments and investigations as advised by the physician.
REFERENCES
- Alventosa-Zaidin M, Font LG, Camps MB, et al. Right bundle branch block: Prevalence, incidence, and cardiovascular morbidity and mortality in the general population. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6713172/ Eur J Gen Pract 2019;25(3):109-115.
- American Heart Association. Heart Conduction Disorders. https://www.heart.org/en/health-topics/arrhythmia/about-arrhythmia/conduction-disorders.
- Harkness WT, Hicks M. Right Bundle Branch Block. https://www.ncbi.nlm.nih.gov/books/NBK507872/. [Updated 2021 Aug 13]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-.
- Koley, T.K. (2024). Bundle Branch Block. In: Rapid Review of ECG. Springer, Singapore. https://doi.org/10.1007/978-981-99-9116-7_14
- Scherbak D, Hicks GJ. Left Bundle Branch Block https://www.ncbi.nlm.nih.gov/books/NBK482167/. [Updated 2021 Aug 1]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-.
- Timóteo AT, Mendonça T, Rosa SA, et al. Prognostic impact of bundle branch block after acute coronary syndrome. Does it matter if it is left or right?. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6279709/ Int J Cardiol Heart Vasc 2019 Mar;22:31-34.
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