Bundle branch block: what it is, causes, symptoms and treatment

The heart beats because electrical impulses travel through it in a set pathway. The BHF explains that a heart block happens when these impulses are blocked or delayed, and that bundle branch blocks are one kind. In a bundle branch block the impulses that travel through the ventricles, the bottom chambers of the heart, are slower than normal because of a block in the path they follow. NHS inform describes it in the same way.

There are two types, because the pathway splits to the left and right sides of the ventricles. The BHF says in left bundle branch block (LBBB) impulses are delayed or blocked to the left ventricle, and in right bundle branch block (RBBB) to the right ventricle.

The two types have different implications, according to the BHF. The ECG pattern also differs: a Patient.info professional reference notes a prolonged QRS complex in both, with an M-shaped pattern in leads over the right side of the heart (V1 and V2) in RBBB and over the left side (such as V5 and V6) in LBBB.

The BHF says the delay in bundle branch block does not often cause symptoms, and NHS inform says bundle branch block does not usually cause any symptoms. Many people discover it only when an ECG is done for another reason, such as a medical check or a heart condition. Unless you have symptoms, heart block is usually diagnosed during testing for another condition.

Any symptoms you do have more often come from an underlying heart condition, or from a higher-degree heart block. For those, the BHF lists feeling faint or dizzy, tiredness and sometimes confusion, pressure or pain in the chest and shortness of breath, and NHS inform lists fainting or collapse, light-headedness, dizziness, breathlessness, chest pain and a slow heartbeat. Discuss any such symptoms with your doctor.

The BHF says RBBB can happen in people with no heart disease or be caused by an underlying heart condition, and that LBBB can be a sign of an underlying heart condition. For heart block more generally, the BHF lists coronary heart disease, congenital heart disease, cardiomyopathy, ageing of the electrical pathways, thickening of the heart muscle and some medicines among causes, and says it can also happen naturally in people with a normal heart. NHS inform adds that most people with heart block develop it later in life or as a result of another condition.

Because the cause matters, doctors often look for a heart condition when LBBB is found, using tests such as an echocardiogram.

The main test is an electrocardiogram (ECG). The NHS says an ECG records the electrical activity of the heart, including rate and rhythm, and is usually quick and painless; sticky patches (electrodes) are attached to the arms, legs and chest. The BHF says the ECG result can show the type of heart block. Your doctor may also want you to wear a portable ECG monitor to record the electrical activity over a longer period.

The BHF adds that an echocardiogram (a scan of the heart similar to an ultrasound) and cardiac MRI may be used to find any underlying condition. The NHS says you may also have an ECG if you have a diagnosed heart condition or before and while taking certain medicines.

The BHF says some heart blocks do not need any treatment, while others do, and the treatment depends on the cause and your symptoms. For bundle branch block that is not causing symptoms, the usual approach is to look for and treat any underlying heart condition and to keep your heart under review. Your doctor will tell you whether you need follow-up ECGs or other tests.

Pacemakers are used for some other forms of heart block. The BHF says second- or third-degree (complete) heart block may need a pacemaker, and NHS inform says third-degree heart block and Mobitz type 2 second-degree block are usually treated with a pacemaker, which is a small device placed under the skin with wires to the heart. NHS inform says first-degree heart block and Mobitz type 1 do not usually need treatment.

It helps to separate bundle branch block from atrioventricular (AV) heart block, where impulses are delayed or blocked between the upper and lower chambers. The BHF describes first-degree, second-degree and third-degree (complete) AV block. NHS inform notes that first-degree block usually causes no symptoms, Mobitz type 1 is the less serious type of second-degree block, and third-degree block can cause fainting, dizziness and breathlessness. The BHF warns that AV heart blocks might turn into higher-degree blocks if left untreated.

The BHF says that if you are worried about having heart block or any heart condition you should speak to your doctor or healthcare team, and if you are worried about your treatment or have questions, they can help answer them. The NHS says you may also have an ECG if you have been diagnosed with a heart condition, and before and while taking certain medicines.

The BHF says to call 999 for an ambulance if you experience severe or sudden symptoms. NHS inform lists symptoms for which to phone 999, including central chest pain or discomfort that does not go away, which may feel like pressure or tightness and can spread to the arm, neck, jaw or back; unconsciousness, seizures or fitting; difficulty breathing; a rapid, low or undetectable heartbeat; and chest pain with breathlessness, sickness, sweating or coughing up blood.

On the NHS, bundle branch block is usually found on an ECG arranged by a GP or hospital doctor, with referral to cardiology if there are symptoms or signs of underlying heart disease. A private cardiology appointment is another route to an echocardiogram or review. The tests and the importance of identifying any underlying condition are the same either way.