When you hear “bundle branch block” on your ECG, you may assume it means a blocked artery. This is one of the most common misconceptions.
In reality, the bundle branches are part of the heart’s electrical system, not blood vessels. A block in this context refers to a delay or interruption in the electrical signal that controls your heartbeat.
Although left bundle branch block (LBBB) can occur in people with coronary artery disease, it doesn’t mean an artery is blocked.
In this article, we explain what LBBB is, how it’s diagnosed, what it may suggest about your heart, and when further tests or treatment may be needed.
What is a Bundle Branch Block?
Your heartbeat is controlled by an internal electrical system. These signals tell your heart muscles when to contract.
The signal travels from the top of the heart (the atria) to the bottom (the ventricles) through specialized pathways.
This electrical pathway splits into two branches, one for each ventricle. The right bundle branch carries the signal to the right side, and the left bundle branch carries it to the left.
A Left Bundle Branch Block means the signal to the left ventricle is slowed or blocked. As a result, the left side of the heart contracts later than the right side.
What Causes LBBB?
LBBB sometimes appears in healthy people. But more often, it relates to underlying heart conditions. These may include:
- High blood pressure (hypertension)
- Coronary artery disease or previous heart attack
- Heart failure or weakened heart muscle (cardiomyopathy)
- Valve disease, especially involving the aortic valve
- Age-related changes in the conduction system
Doctors may find LBBB during an ECG performed for another reason. It can also show up when people report symptoms like chest pain, breathlessness, or palpitations.
What Does LBBB Look Like on an ECG?
LBBB has a distinct pattern on an ECG. It typically shows:
- Widening of the QRS complex (greater than 120 milliseconds)
- Changes in the shape of the QRS in leads V1 and V6
- Absence of the normal small Q wave in the lateral leads
These changes reflect abnormal electrical activation in the left side of the heart. They can also make it harder to detect other problems on the ECG, like a heart attack.
If a new LBBB appears in someone with symptoms such as chest pain or shortness of breath, doctors may treat the situation with extra caution. In this context, the medical team often considers it a possible heart attack until further testing confirms otherwise. This approach ensures that any urgent condition is identified and managed promptly.
Does LBBB Need Treatment?
Treatment depends on your symptoms and whether other heart issues are present.
If LBBB is found in someone with no symptoms and a normal heart, no specific treatment may be required. Regular monitoring may be enough.
However, if LBBB is linked to symptoms or a weakened heart muscle, further testing is usually needed.
Doctors may order echocardiography, cardiac MRI, or stress tests to check heart function and uncover possible causes.
LBBB and Heart Failure
In some people with heart failure and a low ejection fraction, LBBB can make the condition worse. The delay between the left and right sides of the heart can lead to inefficient pumping.
In these cases, a special pacemaker called cardiac resynchronization therapy (CRT) may help. This device improves coordination between the ventricles and can relieve symptoms.
What Should You Do if You’ve Been Told You Have LBBB?
If your ECG shows LBBB, speak with your doctor about what it means in your case. They may suggest more tests to check for underlying problems.
If you have symptoms such as fatigue, breathlessness, or chest discomfort, prompt evaluation is important.
Remember, LBBB is not a disease itself. It is a sign that something in the heart’s electrical or structural system may need attention.
Conclusion
Left bundle branch block is an electrical finding on the ECG. It may or may not relate to structural heart disease.
On its own, LBBB often causes no symptoms. But in some cases, it can point to a more complex heart issue.
With proper assessment and follow-up, most people with LBBB continue to live full, active lives. Staying informed and working closely with your healthcare provider is the best way to manage your heart health.
Peter is an interventional cardiologist and the Founding Editor of Heart Matters, a trusted resource for heart health education. With more than 20 years of clinical experience, he is dedicated to making cardiovascular care more understandable and accessible. His work bridges patient care, research, and public education, empowering individuals to take control of their heart health. Professor Barlis is internationally recognised for his contributions to cardiology, with numerous publications and speaking engagements around the world.
