Overview

Left bundle branch block (LBBB) can occur when there's damage to the heart's electrical system or as an indication of diseases of the heart muscle.¹

In healthy adults, including athletes, LBBB is rare, affecting about 0.1% to 0.8% of people (0.43% in men and 0.28% in women). It becomes more common with age, rising from under 1% at age 50 to 6% by age 80, and is very uncommon in people under 35. Each year, about 3 to 4 out of every 10,000 people in the general population develop LBBB.²

What is the left bundle branch block(LBBB)?

Your heart sends electrical signals to its lower chambers, known as ventricles, to cause them to contract. Usually, both ventricles beat simultaneously in a coordinated rhythm, creating the heartbeat. If you have any underlying heart problems, these electrical signals can be disrupted or blocked from reaching the ventricles, leading to an abnormal heart rhythm. These electrical impulses are transmitted to the right and left ventricles by the right and left bundle branches of the Bundle of HIS, respectively.

In the case of LBBB, the left bundle branch is either partially or completely blocked due to existing health conditions, causing the right ventricle to contract before the left ventricle. This results in the heart being less efficient in pumping an adequate amount of oxygenated blood into the entire circulation in the body.³

What are the causes of LBBB?

Ischaemia

Ischaemia of the heart is caused by narrowing of the heart vessels and is also called coronary artery disease(CAD). This leads to an insufficient supply of blood and oxygen to the heart muscles, giving rise to heart attacks.⁴ Because of decreased blood flow and oxygen supply, the part of the heart responsible for electrical conduction- the left bundle branch of the ‘Bundle of His'- becomes impaired, leading to a disruption in the heart, leading to LBBB. Most of the time, LBBB is associated with reduced blood flow to the heart, typically due to blocked arteries, small vessel disease, or coronary spasms. When LBBB appears on an ECG in a patient with heart-related symptoms, doctors usually check for coronary artery disease or even a heart attack. According to the European Society of Cardiology, a new LBBB, along with raised heart damage markers, confirms a diagnosis of a heart attack.⁵

Several studies have shown that LBBB is a strong sign of a higher risk of death and heart problems in both long-term and sudden coronary artery disease (CAD).⁶

Hypertension

In high blood pressure (hypertension), the heart requires more oxygen because it must pump harder. This thickens the walls of the left ventricle(LV), leading to LV hypertrophy. This strains the heart as it pumps blood. This imbalance of reduced oxygen supply and increased oxygen demand is especially harmful and helps explain why people with high blood pressure are more likely than those with normal blood pressure to develop angina, suffer a heart attack, experience major heart events, and are at a higher risk of death. 

The association of hypertension with the left bundle branch block is a strong indicator for diagnosing coronary artery disease, even in asymptomatic patients. The link between left bundle branch block and preventable risk factors, such as high blood pressure, highlights the importance of managing multiple heart disease risks. Doing so can have a significant impact on public health.⁷

Cardiomyopathy

It can be LBBB-induced cardiomyopathy or LBBB-associated cardiomyopathy. Dilated cardiomyopathy (DCM) occurs when the left side, or both sides, of the heart become enlarged and weakened, without the presence of blocked coronary arteries or other conditions that place excess strain on the heart.⁸  Left bundle branch block (LBBB) is frequently observed in patients with heart failure, especially those with dilated cardiomyopathy (DCM). Traditionally considered a result of DCM, LBBB is now increasingly recognised as a possible cause of DCM, particularly when patients show full recovery of heart function after cardiac resynchronisation therapy (CRT).⁹ This condition is known as LBBB-induced dilated cardiomyopathy (LBBB-iDCM).In LBBB-associated cardiomyopathy, the heart problem is caused by an abnormal electrical signal, making it a potentially reversible condition. ¹⁰

Summary

Although the left bundle branch block (LBBB) has been widely studied, many aspects of its development and associated diseases remain unknown. LBBB is usually not harmless—it is often connected to conditions like high blood pressure, thickened heart muscle, cardiomyopathy, valve disease, heart failure, or coronary artery disease. However, LBBB can also appear in young people with no heart disease and usually has a good outlook in those cases. In older adults with other health problems, LBBB is a known risk factor for serious heart issues.⁵

Recognising LBBB early, especially in specific clinical situations, is essential for choosing the best treatment approach.²

FAQs

How can I reduce my risk of a left bundle branch block?³

While you might not be able to prevent left bundle branch block, adopting simple lifestyle changes can help you manage the condition effectively.

 These include:

• Eat a heart-healthy diet.
• Get regular exercise.
• Monitor your blood pressure regularly.
• Maintain a healthy weight.
• Manage your cholesterol.
• Quit smoking and tobacco use.

When should I schedule an appointment with my healthcare provider?³

Visit your healthcare provider if you have developed any new symptoms or your condition has worsened. 

Symptoms to watch for include:

• Chest pain/discomfort or tightness in your chest.
• Extreme fatigue/tiredness
• Loss of consciousness
• Shortness of breath or difficulty breathing.

How is the left bundle branch block diagnosed?³

The left bundle branch block is diagnosed by your healthcare provider with the help of an electrocardiogram (ECG). ECG graphs can assist in diagnosing LBBB and other cardiovascular conditions. 

The following tests are recommended:

• Blood pressure readings for checking out high or low blood pressure
• Blood test to check cholesterol levels
• An Echocardiogram examines the blood flow in your heart and identifies any underlying heart disease
• A nuclear cardiac stress test to look for coronary artery disease