Why is the left ligament block important?

Left bundle branch block (LBBB) is a condition that is seen on an electrocardiogram (ECG) . In particular, this indicates that the electrical impulse of the heart is not distributed to the ventricles of the heart in the usual way.

LBBB is important because it often indicates the presence of some form of underlying heart disease. On the other hand, right bundle branch block does not signify underlying heart disease. Therefore, anyone diagnosed with a left bundle branch block on an ECG should undergo a cardiac examination.

This article explains the symptoms, causes, diagnosis, and treatment of LBBB.

Get Medical Information / Laura Porter

Packet branching function

The bundle branches are part of the electrical wiring of the heart. These are the pathways that evenly distribute the electrical impulse from the heart through the ventricles, providing a coordinated contraction of the two ventricles.

With left bundle branch block, the bundle branch of His, which transmits an electrical impulse to the left ventricle, is totally or partially blocked. This block delays the response of the left ventricle. As a result, the right ventricle is activated and contracts before the left ventricle is activated.

For the heart to beat efficiently, both ventricles must contract at the same time. Therefore, a left bundle branch block can reduce the efficiency of the heartbeat.

For someone whose heart is otherwise healthy, this reduced function may be trivial. However, in people with heart failure and a decrease in the left ventricular ejection fraction to less than 50%, left bundle branch block can lead to a significant decrease in cardiac efficiency.

This decreased effectiveness can accelerate the heart failure flare and make symptoms significantly worse.


LBBB is usually asymptomatic. However, if you have heart conditions other than LBBB, you are more likely to develop symptoms. Symptoms can include:

  • Difficulty breathing
  • Fatigue
  • Fainting (fainting)


The main cause of LBBB is dilated cardiomyopathy , a heart condition in which a weakened heart cannot contract normally. When the heart muscle tries to compensate for this weakness, it stretches and increases in size.

In most cases, doctors cannot determine the cause of dilated cardiomyopathy. However, certain factors can increase your risk of developing the disease, including:

BRI mainly affects the elderly. For example, it occurs in less than 1% of people under the age of 50; In contrast, nearly 6% of 80-year-olds have a left bundle branch block.

LBBB value

  • Left bundle branch block is most often caused by an underlying heart problem. Therefore, when the doctor discovers this, it is very likely that some type of serious heart condition is also present.
  • LBBB itself makes the heart work slightly less efficiently, which is important for people with certain types of heart disease.


Left bundle branch block produces characteristic ECG changes. Therefore, doctors can usually diagnose this condition by looking at the results of these tests.

A standard ECG recording shows 12 different views of the heart's electrical activity. These images are transmitted by ten electrodes (or "wires") attached to the body.

QRS complex

The part of the ECG called the QRS complex is an electrical impulse that travels through the ventricles.

Usually, due to the simultaneous pacing of both ventricles, the QRS complex is relatively narrow, usually between 0.08 and 0.1 seconds. However, the QRS complex is much wider with left bundle branch block, often lasting 0.12 seconds.

Doctors can examine the electrical activity of the heart to locate various heart problems. For example, with a left bundle branch block, a wide QRS complex appears vertical in some leads and downward in others.

Differential diagnosis

Most people with left bundle branch block have some type of underlying heart disease. Therefore, anyone of any age who has LBBB should have a cardiac exam to identify an underlying heart condition.

The most common comorbidities include:

In one study, 47.7% of people with left bundle branch block also had high blood pressure.

During an early historical study in cardiology, 89% of people who developed left bundle branch block were later diagnosed with some form of serious cardiovascular disease.

If you have risk factors for coronary heart disease, your doctor may order additional tests, including:

If, after a complete heart exam, your doctor finds no signs of heart disease, especially if you are under the age of 50, the prognosis is good. In these cases, a left bundle branch block is considered an accidental benign ECG finding.

About a third of people with heart failure also have LBBB.

Watch out

People without heart disease may not need treatment. However, cardiac resynchronization therapy (CRT) or a pacemaker may be options for patients with an underlying medical condition.


People with significant heart failure may be good candidates for cardiac resynchronization therapy (CRT). CRT is a type of pacemaker that coordinates the contraction of the ventricles. It can significantly improve cardiac efficiency in people with LBBB and heart failure.

Unless there is a reason for a CRT pacemaker to change ventricular coordination, most people with LBBB never need a pacemaker. However, in some cases, the presence of LBBB may indicate an underlying heart condition.

Chronic pacemaker therapy

A typical permanent pacemaker stimulates the heart with a pacemaker lead located in the right ventricle. Because the electrical impulse from the pacemaker stimulates the right ventricle versus the left ventricle, people with permanent pacemakers essentially have a pacemaker-induced left bundle branch block.

In recent years, some evidence suggests that people with low left ventricular ejection fraction with permanent pacemakers may be at increased risk of developing heart failure due to pacemaker-induced left bundle branch block.

For this reason, some experts now routinely use CRT pacemakers (which prevent pacemaker-induced left bundle branch block) in people with reduced ejection fraction who are completely dependent on permanent pacemakers.

If you have heart disease, the electrical signal from your heart can be interrupted in a number of ways. When this happens, significant bradycardia (slow heart rate) can develop over time. In this case, you may need a permanent pacemaker. For this reason alone, people with LBBB should have regular checkups.


LBBB is a condition in which the heart's electrical impulses are not evenly distributed. Often, but not always, the presence of LBBB indicates an underlying heart condition. The most common heart disease that leads to LBBB is dilated cardiomyopathy.

Doctors diagnose LBBB with an EKG. If there is no underlying heart disease, treatment may not be necessary. However, if you have heart disease, especially heart failure, you may need a CRT pacemaker or a permanent pacemaker.

Get the word of drug information

If you've been diagnosed with LBBB, be sure to have a cardiac exam to determine the underlying heart condition. Rest assured that not everyone with LBBB has heart disease, but it is important to rule it out.

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