Left Bundle Branch Block (LBBB): Causes, Symptoms, and Treatment

left bundle branch blockLeft bundle branch block or LBBB is essentially a blockage of electrical impulses to the heart’s left ventricle, which is the lower-left part of the heart. Knowing how the heart works is the first step to understanding the underlying causes of LBBB and how to go about treating it.

The best way to explain left bundle branch block is to describe how the heart works. Left bundle branch block takes place when electrical impulses conducted by heart tissue experience a block at the left or right branch of the “bundle of His.” The bundle of His is an area of the heart that normally conducts impulses to the left and right ventricles.


When the heart beats properly, its tissue conducts electrical impulses throughout the muscle in a pattern. When an area is blocked, this means the electrical impulse has to travel longer to reach its endpoint. In other words, it’s harder for the heart to pump blood through the body.

The upper chambers of the heart are the atria and the lower chambers are the ventricles. If you have a healthy heart, the electrical signal to start your heartbeat starts in the upper chamber before traveling to the lower chamber. While the signal travels, it triggers parts of the heart to contract. With LBBB, the left ventricle contracts a little later than it should, leading to uncoordinated contractions.

What Is Incomplete Left Bundle Branch Block?

There is a condition called incomplete left bundle branch block. It means that the electrical impulse is diminished but eventually does pass the block. On an electrocardiogram (ECG), a QRS complex is the name of the three graphical deflections recorded.

Some people call it the “main spike” on the test line. QRS complex with incomplete left bundle branch block resembles complete left bundle branch block, which is typically about 0.12 seconds. Unfortunately, incomplete left bundle branch block often progresses to complete left bundle branch block.

What Are the Causes of Left Bundle Branch Block?

Left bundle branch block causes are often due to a heart condition of some sort. Sometimes, LBBB can happen when the structure of the heart is normal, so researchers are still looking into what causes left bundle branch block.

Here are some heart conditions that could result in LBBB:

  • Heart attack
  • Coronary artery disease
  • High blood pressure
  • Cardiomyopathy – enlarged or weakened heart muscle
  • Myocarditis – heart infection
  • Heart valve disease
  • Congenital heart defects
  • Certain heart rhythm medicines
  • Aortic valve problems

Symptoms of Left Bundle Branch Block

Left bundle branch block symptoms do not appear in every case – some people just don’t experience any signs. The main symptom, if any, is syncope. Syncope is fainting that occurs as a result of unusual heart rhythms that impact blood pressure. Some individuals may also report having pre-syncope, which means that they feel like they are going to faint but never do.

Some research suggests that left bundle branch block increases the risk of getting heart disease, which comes with another setup signs and symptoms, including chest discomfort.

Why You Should Be Worried about LBBB

You may be wondering, is left bundle branch block dangerous? A diagnosis of left bundle branch block is significant because it’s usually brought on due to an underlying heart problem.
Additionally, LBBB itself can cause the heart to work less efficiently in some people who suffer from heart diseases.

There are left bundle branch block risks. LBBB has been linked to hypertension, ventricular hypertrophy, valvular heart disease, myocarditis, ischemic heart disease, heart failure, as well as cardiomyopathies. The Framingham Heart Study indicated that LBBB was associated with seven times as great a risk of heart failure.

Left Ventricular Hypertrophy and Incomplete LBBB

When someone is experiencing left ventricular hypertrophy, the mass of their left ventricle has likely increased. The word “hypertrophy” literally means thickening. Left ventricle hypertrophy forces the heart to work harder. The enlargement of the left ventricle can lead to an increased QRS duration but not 0.12 seconds or longer, as can be seen sometimes with a left bundle branch block ECG. With left ventricular hypertrophy, the QRS complex can have large amplitude though.

Left ventricular hypertrophy is seen more in people who have uncontrolled high blood pressure. This condition puts you at a higher risk of having a heart attack or a stroke.

Left Bundle Branch Block and Cardiac Efficiency

In cases of left bundle branch block, the left ventricle is stimulated after the right ventricle is stimulated. This lack of coordination between the two ventricles decreases the efficiency of the heartbeat, forcing the heart to have to work harder to achieve normal pumping capacity.

In relatively healthy individuals, the drop in cardiac efficiency doesn’t cause that much of a problem; however, if a person has heart issues, such as heart failure and a left ventricular ejection fraction less than 35 percent, the reduced efficiency can further heart deterioration. Left ventricular ejection fraction (LVEF) is the percentage of blood in the left ventricle being pumped out with each heartbeat. A normal LVEF range is from 55 percent to 70 percent.

How Is Left Bundle Branch Block Diagnosed?

Left bundle branch block diagnosis is normally determined by analyzing an ECG. The QRS complex is the part of the ECG that represents electrical impulse distributed across the right and left ventricles. Under normal conditions, both ventricles are stimulated at the same time so the QRS is rather narrow – for example, 0.08 and 0.1 seconds long.

However, with left bundle branch block, the QRS is much wider. The ECG also shows twelve different views of electrical activity in the heart. Doctors can look at these views in order to get a better sense of various heart problems. In people with left bundle branch block, the QRS complex often appears upright in certain views and downward in others. Between the QRS duration and the pattern of various views on an ECG, a doctor can usually determine whether or not LBBB is the problem.

Aside from an ECG, the doctor may also conduct a cardiac stress test to look for coronary artery disease or any other abnormalities. Blood work to test cholesterol levels, as well as other factors, are standard practice.

Treatment for Left Bundle Branch Block

Left bundle branch block treatment is not required in every case. Those who don’t have any serious underlying heart conditions may not need a lot of medical intervention. If you have a heart condition already, treatment for left bundle branch block will probably involve addressing the underlying cause of that condition.

If you have had a heart attack and are then diagnosed with LBBB, you may need a pacemaker. A pacemaker is a device that emits electricity to help your heart stay in a consistent rhythm. Those who have high blood pressure may be treated with medications to keep the pressure at acceptable levels, which can reduce strain on the heart.


It is important to know that treating an underlying condition will not cure the left bundle branch block, but it can lessen the severity and help prevent further damage.

Left bundle branch block sounds frightening but in the majority of cases, it is not as serious as it sounds. In fact, some people don’t even realize that they have LBBB. If you have LBBB with symptoms, a doctor will come up with a plan to address the underlying cause and help you cope better physically and psychologically with the diagnosis.

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