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What Is a Left Anterior Fascicular Block?

By RJ Lawrence
Updated Mar 03, 2024
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A left anterior fascicular block (LAFB) is the medical name given to scarring or other blockage that causes portions of the heart’s left ventricle to shrink or constrict. On its own it isn’t necessarily harmful and people who have this condition may not even realize it. The blockage has been linked to a number of other heart problems like heart attack and congestive heart failure, though, and can also cause trouble when it comes to controlling the flow of blood pumping through the heart. The LAFB isn’t itself a failure, but it can make failures more likely and it does indicate a certain degree of damage. Medical experts aren’t exactly sure why these sorts of blocks happen, but lifestyle choices and genetics are often influential. People who smoke, consume excessive alcohol, and eat diets high in artery-clogging cholesterol are often more at risk. Medical experts often only notice the blocks on heart scans, and there aren’t usually any outward symptoms when the scarring is fresh. There isn’t usually a way to reverse the damage, either, but knowing about the condition can help people make changes that can prevent bigger problems down the line.

Understanding Heart Impulses

The human heart is made up of a series of chambers known as atria and ventricles, and there are two of each on each side: a right and a left. 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. Most of the time this happens because the arteries and channels leading to it are thickened, blocked, or otherwise narrowed.

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. This happens primarily if the failure is centered 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. The result is usually a delayed activation of the anterior portion of the heart's left ventricle. At first this is usually barely noticeable, but can cause heart rhythm issues and other problems if it continues to progress.

Main Reasons Blocks Happen

There are many potential causes of a left anterior fascicular block, including chronic high blood pressure, lung disease, aging, and degenerative fibrotic disease. A lot depends on the individual and his or her age. Sometimes there is no known cause for the scarring and constriction, but many medical experts think that certain lifestyle choices can make the condition more likely. Things that put stress on the heart, like smoking and consuming alcohol, may trigger it, for instance. People with poor diets and those who don’t engage in regular cardiovascular activities like walking or moderate exercise may also be more at risk.

Symptoms and Initial Diagnosis

People who have this sort of blockage in their heart don’t typically notice it at first. Mild scarring is often only detected on an electrocardiogram (ECG) scan or other diagnostic test that measures the heart’s beating pattern. Patients who have this condition often have a slight delay in the pulsations from the left side of the heart, but in mild and early cases this doesn’t usually cause any outward signs. As things progress, though, people may experience intermittent or recurring chest pain and dizziness.

Relationship to Other Heart Conditions

A LAFB is the most common intraventricular conduction defect associated with myocardial infarction, commonly known as a heart attack. This doesn’t mean that the blockage necessarily causes the infarction, but researchers have noticed a pattern of the two going hand-in-hand in many patients. People who have these sorts of blockages also appear to be more prone to congestive heart failure and a condition known as “atrial fibrillation.”

Treatment Options

Medical experts usually recommend that people who have been diagnosed with LAFB take immediate steps to reduce their risk of developing more serious heart complications. There isn’t usually any way to undo the damage, but there are a number of things people can do to make sure that the damage doesn’t get any worse.

A patient might be advised to take certain supplements, such as omega-3 fatty acids, for instance, or he or she may be told to eat a diet that is high in protein and low in carbohydrates and fats. Exercising regularly at a moderate pace that won't provoke cardiac episodes is often recommended, too. LAFB patients are generally 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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