From the Guidelines
Patients with bundle branch block (BBB) and symptoms such as syncope, or those with a high-risk profile including a wide QRS complex, should receive a pacemaker or cardiac resynchronization therapy (CRT) as indicated, to reduce morbidity and mortality. The management of conduction disorders, including BBB, is guided by the 2018 ACC/AHA/HRS guideline on the evaluation and management of patients with bradycardia and cardiac conduction delay 1.
Key Considerations
- Syncope in the presence of BBB with a His-ventricular (HV) interval >70ms is an indication for permanent pacing (Class I) 1.
- Alternating BBB also warrants permanent pacing (Class I) 1.
- For patients with left ventricular ejection fraction (LVEF) 36-50%, left bundle branch block (LBBB), QRS >150 ms, and Class II or greater heart failure symptoms, cardiac resynchronization therapy (CRT) may be considered (Class IIb) 1.
Diagnostic Approach
- The diagnosis of BBB is typically made on an electrocardiogram (ECG), with specific patterns distinguishing right bundle branch block (RBBB) from left bundle branch block (LBBB).
- Further evaluation, including echocardiography and possibly stress testing or coronary angiography, is crucial for patients with LBBB to assess for underlying structural heart disease.
Treatment Implications
- The decision to implant a pacemaker or CRT should be based on the presence of symptoms, the width of the QRS complex, and the patient's overall heart failure status, as these factors influence the risk of developing complete atrioventricular block or experiencing sudden cardiac death 1.
- For certain conditions like Kearns-Sayre syndrome or Anderson Fabry disease, where there is a high incidence of atrioventricular block and sudden cardiac death, prophylactic pacing may be considered on a case-by-case basis 1.
From the Research
Definition and Causes of Bundle Branch Block
- A bundle branch block is a condition where there is a delay or obstruction in the electrical conduction system of the heart, specifically in the bundle branches that carry electrical impulses to the ventricles 2.
- Left bundle branch block may be due to conduction system degeneration or a reflection of myocardial pathology, and may also develop following aortic valve disease or cardiac procedures 2.
- Right bundle branch block can also occur, and both types of bundle branch block can have significant clinical implications 3.
Clinical Presentation and Outcomes
- Patients with acute myocardial infarction and bundle branch block may have worse prognosis compared to those with isolated ST segment elevation 3.
- Bundle branch block patients are often older and have more pre-existing cardiovascular conditions, and may present with pulmonary oedema and cardiogenic shock 3.
- Mortality rates are higher in patients with left bundle branch block compared to those with right bundle branch block or ST segment elevation, although this may be influenced by underlying clinical characteristics and treatment decisions 3, 4, 5.
Treatment and Management
- Cardiac resynchronization therapy may be beneficial for patients with heart failure and left bundle branch block, although lead placement and other technical considerations are important 2.
- Patients with acute myocardial infarction and bundle branch block may be less likely to receive optimal therapy, including reperfusion therapy and medications such as aspirin and beta-blockers 4, 5.
- Echocardiographic coronary flow assessment may be a useful tool for evaluating coronary artery disease in patients with left bundle branch block, and can help guide clinical decision-making 6.
Trends and Outcomes
- Mortality rates for patients with left bundle branch block have decreased over time, although there may still be room for improvement in treatment and outcomes 5.
- Further research is needed to better understand the clinical implications of bundle branch block and to identify optimal treatment strategies for patients with this condition 3, 5, 6.