What Is a Left Anterior Fascicular Block?

A left anterior fascicular block occurs when there is an interruption of electrical impulses in the heart.
A left anterior fascicular block is commonly associated with a heart attack.
LAFB patients should not drink or smoke.
A left anterior fascicular block will be easily recognized using an ECG.
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  • Written By: RJ Lawrence
  • Edited By: A. Joseph
  • Last Modified Date: 12 October 2014
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A Left Anterior Fascicular Block (LAFB) is a medical condition that involves the failure or interruption of electrical impulses in the heart. It occurs specifically when the failure happens in the left anterior, or front, portion of an area called the His bundle, which is a group of muscle fibers that are responsible for transmitting electrical impulses from one part of the heart to another. This condition causes a delayed activation of the anterior portion of the heart's left ventricle. Also known as a left anterior hemiblock (LAH), this condition is easily identified through an electrocardiogram (ECG), a test that checks for problems in the electrical activity of the patient's heart.

In a normally functioning heart, electrical impulses activate the left ventricle by passing through the left bundle branch, a part of the heart that consists of an anterior fascicle, or bundle, and a posterior fascicle. A left anterior fascicular block occurs after this transmission has proceeded as usual along the left posterior fascicle but is stopped, interrupted or delayed in the anterior fascicle. If the impulse is blocked or delayed in the left posterior fascicle, it is called a left posterior fascicle block, or left posterior hemiblock, and when both of these conditions occur at the same time, it is called a left bundle branch block.


A LAFB is the most common intraventricular conduction defect associated with myocardial infarction, commonly known as a heart attack. There are many potential causes of a left anterior fascicular block, including chronic high blood pressure, lung disease, aging and degenerative fibrotic disease. Common symptoms include the ventricles beating at different times, intermittent or recurring chest pain and dizziness.

The treatment for left anterior fascicular block depends on the degree of blockage, but it tends to follow a thorough cardiac evaluation, including an ECG, to determine the extent of LAFB. A patient might be advised to take certain supplements, such as omega-3 fatty acids; to eat a diet that is high in protein and low in carbohydrates and fats; and to exercise regularly at a moderate pace that won't provoke cardiac episodes. LAFB patients are discouraged from drinking and smoking, because alcohol and nicotine tend to cause a narrowing of the blood vessels, which can compromise blood circulation and increase the risk of heart problems.


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