Medically reviewed by Dr Nabila Laskar, Consultant Cardiologist (GMC 7040901). Bundle branch block is an ECG finding indicating that the electrical signal travelling through the heart's conduction system is delayed or blocked in one of the two bundle branches that deliver the impulse to the ventricles. It is a common incidental finding, particularly right bundle branch block, and its significance depends primarily on which branch is affected and whether underlying heart disease is present.
Normally, the electrical impulse from the AV node travels simultaneously down the left and right bundle branches, activating both ventricles in a coordinated, synchronised sequence. When one branch is blocked, the affected ventricle is activated later than normal via a slower alternative route, producing the characteristic widened QRS complex on the ECG and an abnormal activation pattern.
RBBB is the more common of the two and is frequently found as an isolated incidental finding in otherwise healthy individuals with no structural heart disease. In the absence of symptoms or other cardiac pathology, isolated RBBB in a young or middle-aged person generally requires no treatment beyond a baseline echocardiogram to confirm normal cardiac structure. That said, RBBB can also be associated with pulmonary embolism, congenital heart disease, and in older patients, ischaemic heart disease, so clinical context determines how it is investigated.
LBBB carries a more significant clinical implication than RBBB. New LBBB should always prompt further investigation to exclude coronary artery disease, cardiomyopathy, and other structural causes. It can also indicate significant conduction system disease. LBBB also complicates ECG interpretation because it alters the ST segments in a way that mimics and can mask the changes of an acute heart attack. An echocardiogram is essential when LBBB is found, and in selected patients further imaging or stress testing is appropriate.
The most important immediate step is a cardiology consultation with a baseline echocardiogram. In most people with RBBB and no symptoms, this will provide reassurance. In LBBB, or where symptoms such as breathlessness, dizziness, or syncope are present, further assessment is warranted. Bundle branch block does not typically cause symptoms itself but may be a marker of an underlying condition that does.
Isolated RBBB without other cardiac pathology is generally not dangerous. LBBB warrants further investigation as it is more commonly associated with underlying structural heart disease.
Rate-dependent bundle branch block resolves when heart rate returns to a normal range. Fixed bundle branch block does not typically resolve spontaneously, though it may improve if an underlying cause such as hypertension is treated.
Most people with bundle branch block do not require a pacemaker. Pacemakers are considered when there is evidence of more extensive conduction system disease causing significant pauses or heart block requiring treatment.
Book a cardiology consultation and echocardiogram. In most cases this will confirm an entirely normal heart structure and provide clear reassurance. No GP referral is required at The Cardiology Doctors.