Left Posterior Fascicular Block

What is a left posterior fascicular block?

Left posterior fascicular block is an issue in the transmission of electrical signals in the left ventricle of your heart.

How are electrical signals transmitted in the heart?

Your heart has four chambers. These include two upper chambers (atria) and two lower chambers (ventricles).

Electrical impulses control your heartbeat and tell your atria and ventricles to contract. The electrical signals follow a specific pathway through your heart. They start in your atria and move to your ventricles. This creates the “lub-dub” noise your heart makes when it beats.

A network of nerves carries these electrical impulses through your heart. Each ventricle has a main bundle of nerves that run down the center of your heart. These are called the right bundle branch and left bundle branch. The left bundle branch splits into two smaller bundles called fascicles:

• Left posterior fascicle, wraps around the back of your left ventricle.
• Left anterior fascicle, wraps around the front of your left ventricle.

Usually, your anterior and posterior fascicles work together to signal your left ventricle to contract.

In left posterior fascicle block, your left posterior fascicle is either partially or completely blocked. Thus, your left anterior fascicle steps in to control contraction of your left ventricle. This changes the direction of the electrical impulse and delays it, leading to an irregular heartbeat (arrhythmia).

Left posterior fascicular block can occur on and off or continuously.

How common is left posterior fascicular block?

Among healthy people, left posterior fascicular block is rare. It’s more common in people with heart conditions.

Left posterior fascicular block may be accompanied by a right bundle branch block, which is a similar condition where electrical signals are blocked on the right side. When these types of blocks occur together, they can be fatal.

What causes left posterior fascicular block?

It occurs when the electricity in your heart becomes damaged. The main causes of this damage are heart diseases and conditions, such as:

• Coronary artery disease: Lack of blood flow to your heart due to clogged arteries can damage your heart. This is the most common underlying condition.
• Cardiomyopathy: A group of conditions in which your heart muscle becomes stiff, thickened or enlarged.
• High blood pressure (hypertension).
• Lenègre disease: An inherited condition that affects the conduction of electrical signals in your heart.
• Lev’s disease: Nerve fibers in your heart become scarred, reducing their ability to transmit electrical signals. This is associated with aging.

What are the symptoms of left posterior fascicular block?

Typically, left posterior fascicular block doesn’t cause symptoms. People may experience symptoms related to the disease that’s causing it.

How is left posterior fascicular block diagnosed?

The main tool for diagnosing left posterior fascicular block is an electrocardiogram (ECG/EKG). This test measures the electrical activity of your heart.

Your healthcare provider may also perform an EKG while you exercise to measure your heart’s activity under stress. This is an exercise stress test. Sometimes, it shows left posterior fascicular blocks that weren’t detected on an initial resting EKG.

The EKG signals of left posterior fascicular block and other conditions, such as a heart attack (myocardial infarction), can interfere with each other. Your healthcare provider will ask about your medical history and perform a physical exam. This helps them make an accurate diagnosis and avoid a delay in treatment for a more serious condition.

How is left posterior fascicular block treated?

Treatment is focused on managing the underlying condition that’s causing the block. For heart diseases, such as coronary artery disease or cardiomyopathy, healthcare providers use a variety of treatments including:

• Lifestyle changes.
• Medications.
• Minimally invasive procedures.
• Surgery.

If you have left posterior fascicular block and right bundle branch block, your healthcare provider may recommend a pacemaker. This implanted device monitors your heart’s electrical activity and sends electrical signals so your ventricles contract together.

If you have left posterior fascicular block without other heart conditions, you won’t need treatment.

How can I prevent left posterior fascicular block?

Prevention depends on preventing the heart conditions that cause it. Routine checkups with your primary care provider are important because early detection of heart problems can prevent serious outcomes.

Healthy habits that can help prevent many types of heart conditions include:

• Consuming a healthy diet.
• Controlling your blood pressure.
• Exercising routinely.
• Limiting alcohol and caffeine.
• Maintaining a healthy weight.
• Managing stress.
• Quitting smoking and smokeless tobacco.

If you have an existing heart condition, follow your healthcare provider’s instructions. This can help prevent further complications, such as a left posterior fascicular block.

What is the prognosis for people with left posterior fascicular block?

Most often, left posterior fascicular block and right bundle branch block occur together. If you have a heart attack, having left posterior fascicular block and right bundle branch block increases your risk of death. Sometimes, a person with both blocks can develop a complete block of electrical impulses in their ventricles. The outlook of this condition is poor.

If you don’t have right bundle branch block or underlying heart disease, your life expectancy doesn’t change with left posterior fascicular block.

When should I contact my healthcare provider?

Talk to your healthcare provider if you have any signs and symptoms of heart disease, including:

• Chest pain.
• Dizziness or fainting.
• Fatigue.
• Heart palpitations, including racing, pounding or skipped heartbeats.
• Lightheadedness.
• Nausea.
• Persistent cough.
• Shortness of breath.
• Swelling in your feet, ankles, legs or abdomen.

A note from Cleveland Clinic

Left posterior fascicular block usually occurs in people who have other types of heart disease. If you have a heart condition, your healthcare provider will recommend a treatment plan and monitor you closely. By following your provider’s advice and attending routine appointments, you can manage your heart condition and prevent a more serious cardiac event.