Left anterior fascicular block and right bundle branch block

Q: What is right bundle branch block with LAFB?

RBBB + LAFB is the most common of the two patterns. This is due to a single coronary artery blood supply (LAD) to the anterior fascicle. RBBB + LPFB is less common due to a dual blood supply (right and left circumflex arteries), and this combination may be associated with more extensive underlying cardiac pathology.

Q: Is Fascicular block the same as bundle branch block?

Bundle branch block is partial or complete interruption of impulse conduction in a bundle branch; fascicular block is similar interruption in a hemifascicle of the bundle. The 2 disorders often coexist. There are usually no symptoms, but presence of either suggests a heart disorder. Diagnosis is by electrocardiography.

Q: Is left anterior fascicular block the same as left bundle branch block?

Left anterior fascicular block (LAFB) is an abnormal condition of the left ventricle of the heart, related to, but distinguished from, left bundle branch block (LBBB). It is caused by only the left anterior fascicle – one half of the left bundle branch being defective.

Q: Should I worry about left anterior fascicular block?

A cardiac condition called left anterior fascicular block (LAFB), in which scarring occurs in a section of the left ventricle, may not be as benign as currently thought and could increase the likelihood of heart failure, sudden cardiac death or atrial fibrillation.

Overview

Bundle branch block is a condition in which there's a delay or blockage along the pathway that electrical impulses travel to make the heart beat. It sometimes makes it harder for the heart to pump blood to the rest of the body.

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When to see a doctor
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Left bundle branch block
Right bundle branch block
Risk factors
Complications
Clinical Presentation and Diagnosis
Clinical presentation
Right bundle branch block on ECG ECG An electrocardiogram (ECG) is a graphic representation of the electrical activity of the heart plotted against time. Adhesive electrodes are affixed to the skin surface allowing measurement of cardiac impulses from many angles. The ECG provides 3-dimensional information about the conduction system of the heart, the myocardium, and other cardiac structures. Electrocardiogram (ECG)
LBBB on ECG ECG An electrocardiogram (ECG) is a graphic representation of the electrical activity of the heart plotted against time. Adhesive electrodes are affixed to the skin surface allowing measurement of cardiac impulses from many angles. The ECG provides 3-dimensional information about the conduction system of the heart, the myocardium, and other cardiac structures. Electrocardiogram (ECG)
Incomplete RBBB and LBBB
Left anterior fascicular block on ECG ECG An electrocardiogram (ECG) is a graphic representation of the electrical activity of the heart plotted against time. Adhesive electrodes are affixed to the skin surface allowing measurement of cardiac impulses from many angles. The ECG provides 3-dimensional information about the conduction system of the heart, the myocardium, and other cardiac structures. Electrocardiogram (ECG)
Left posterior fascicular block on ECG ECG An electrocardiogram (ECG) is a graphic representation of the electrical activity of the heart plotted against time. Adhesive electrodes are affixed to the skin surface allowing measurement of cardiac impulses from many angles. The ECG provides 3-dimensional information about the conduction system of the heart, the myocardium, and other cardiac structures. Electrocardiogram (ECG)
Related videos
What is right bundle branch block with LAFB?
Is Fascicular block the same as bundle branch block?
Is left anterior fascicular block the same as left bundle branch block?
Should I worry about left anterior fascicular block?

The delay or blockage can occur on the pathway that sends electrical impulses either to the left or the right side of the bottom chambers (ventricles) of the heart.

Bundle branch block might not need treatment. When it does, treatment involves managing the underlying health condition, such as heart disease, that caused bundle branch block.

Symptoms

In most people, bundle branch block doesn't cause symptoms. Some people with the condition don't know they have bundle branch block.

Rarely, symptoms of bundle branch block may include fainting (syncope) or feeling as if you're going to faint (presyncope).

When to see a doctor

If you've fainted, see a health care provider to rule out serious causes.

If you have heart disease or have been diagnosed with bundle branch block, ask your provider how often you should have follow-up visits.

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Causes

Electrical impulses within the heart muscle cause it to beat (contract). These impulses travel along a pathway, including two branches called the right and the left bundles. If one or both of these branch bundles are damaged — due to a heart attack, for example — the electrical impulses can become blocked. As a result, the heart beats irregularly.

The cause for bundle branch blocks can differ depending on whether the left or the right bundle branch is affected. Sometimes, there is no known cause.

Causes can include:

Left bundle branch block

Heart attack (myocardial infarction)
High blood pressure (hypertension)
Inflammation of the heart muscle (myocarditis)
Thickened, stiffened or weakened heart muscle (cardiomyopathy)

Right bundle branch block

Blood clot in the lungs (pulmonary embolism)
Heart attack (myocardial infarction)
Heart structure problems that are present at birth (congenital heart defects) — such as a hole in the wall separating the upper chambers of the heart (atrial septal defect)
High blood pressure in the pulmonary arteries (pulmonary hypertension)
Inflammation of the heart muscle (myocarditis)

Risk factors

Risk factors for bundle branch block include:

Increasing age. Bundle branch block is more common in older adults than in younger people.
Underlying health problems. Having high blood pressure or heart disease increases the risk of having bundle branch block.

Complications

If both the right and the left bundles are blocked, the main complication is a complete blockage of the electric signaling from the upper to the lower chambers of the heart. The lack of signaling can slow the heart rate. A slowed heart rate may lead to fainting, irregular heart rhythms and other serious complications.

Because bundle branch block affects the electrical activity of the heart, it can sometimes complicate the accurate diagnosis of other heart conditions, especially heart attacks. It may lead to delays in proper management of those heart conditions.

Clinical Presentation and Diagnosis

Clinical presentation

Usually asymptomatic
Most people are unaware.
Rarely, may cause syncope Syncope Syncope is a short-term loss of consciousness and loss of postural stability followed by spontaneous return of consciousness to the previous neurologic baseline without the need for resuscitation. The condition is caused by transient interruption of cerebral blood flow that may be benign or related to a underlying life-threatening condition. Syncope or presyncope Presyncope Syncope (may have associated AV block AV block Atrioventricular (AV) block is a bradyarrhythmia caused by delay, or interruption, in the electrical conduction between the atria and the ventricles. Atrioventricular block occurs due to either anatomic or functional impairment, and is classified into 3 types. Atrioventricular block (AV block))
A split S1 S1 Heart Sounds is common in RBBB.
A split S2 S2 Heart Sounds can also be noted:
- Persistent in RBBB → delayed pulmonic valve closure (due to delayed activation of the right ventricle)
- Paradoxical in LBBB → delayed aortic valve Aortic valve The valve between the left ventricle and the ascending aorta which prevents backflow into the left ventricle. Heart: Anatomy closure (due to delayed activation of the left ventricle)

Audio:

This audio clip is an example of a split S2 S2 Heart Sounds in the setting of an RBBB. The 2 sounds occurring during S2 S2 Heart Sounds result from delayed closure Delayed Closure Gastroschisis of the pulmonic valve in relation to the aortic valve Aortic valve The valve between the left ventricle and the ascending aorta which prevents backflow into the left ventricle. Heart: Anatomy.

Heart sound by The Regents of the University of Michigan. License: CC BY-SA 3.0

A diagram of a paradoxical split in closure of the aortic valve Aortic valve The valve between the left ventricle and the ascending aorta which prevents backflow into the left ventricle. Heart: Anatomy which is delayed:
The name “paradoxical” is due to the fact that the split narrows with inspiration Inspiration Ventilation: Mechanics of Breathing (right). This can be heard in some individuals with a left bundle branch block.

Image by Lecturio.

Right bundle branch block on ECG ECG An electrocardiogram (ECG) is a graphic representation of the electrical activity of the heart plotted against time. Adhesive electrodes are affixed to the skin surface allowing measurement of cardiac impulses from many angles. The ECG provides 3-dimensional information about the conduction system of the heart, the myocardium, and other cardiac structures. Electrocardiogram (ECG)

QRS duration ≥ 120 msec
Leads V1 and V2:
- Rsr′, rsR’ or rSR’ (many variations)
- The R’ or r’ deflection is usually wider than the initial R wave.
- Appears as “rabbit ears”
Leads I and V6 will have an S wave that is:
- Deep
- Of longer duration
- Slurred
T waves tend to be discordant to the terminal QRS vector.

QRS morphology QRS morphology Electrocardiogram (ECG) seen in right bundle branch block:
The RsR’ (and variations of this) give the appearance of “rabbit ears.” The S wave in leads I and V6 will appear broad, deep, and slurred.

Image by Lecturio.

ECG ECG An electrocardiogram (ECG) is a graphic representation of the electrical activity of the heart plotted against time. Adhesive electrodes are affixed to the skin surface allowing measurement of cardiac impulses from many angles. The ECG provides 3-dimensional information about the conduction system of the heart, the myocardium, and other cardiac structures. Electrocardiogram (ECG) demonstrating a right bundle branch block:
The QRS duration is prolonged, at 140 msec. Note the rSR’ and RSr’ in leads V1 and 2, along with the deep and broad S waves in I and V6.

Image by Lecturio.

LBBB on ECG ECG An electrocardiogram (ECG) is a graphic representation of the electrical activity of the heart plotted against time. Adhesive electrodes are affixed to the skin surface allowing measurement of cardiac impulses from many angles. The ECG provides 3-dimensional information about the conduction system of the heart, the myocardium, and other cardiac structures. Electrocardiogram (ECG)

QRS duration > 120 msec in adults
Broad notched (R,R’) or slurred R wave in leads I, aVL, V5, and V6
Absent Q waves in lateral leads
Large S wave in V1 and V2
ST segments and T waves are usually discordant to QRS complex QRS complex Electrocardiogram (ECG).

ECG ECG An electrocardiogram (ECG) is a graphic representation of the electrical activity of the heart plotted against time. Adhesive electrodes are affixed to the skin surface allowing measurement of cardiac impulses from many angles. The ECG provides 3-dimensional information about the conduction system of the heart, the myocardium, and other cardiac structures. Electrocardiogram (ECG) patterns in left bundle branch block:
A large S wave will be seen in V1, while a large, notched R wave occurs in V5 and V6. Note that the ST-segment and T-wave directions are discordant to the QRS.

Image by Lecturio.

ECG ECG An electrocardiogram (ECG) is a graphic representation of the electrical activity of the heart plotted against time. Adhesive electrodes are affixed to the skin surface allowing measurement of cardiac impulses from many angles. The ECG provides 3-dimensional information about the conduction system of the heart, the myocardium, and other cardiac structures. Electrocardiogram (ECG) demonstrating a left bundle branch block:
Note the widened QRS; the large, notched R waves in V5 and V6; and the large, broad S waves in V1 and 2. The ST segments and T waves are also generally discordant to the QRS complex QRS complex Electrocardiogram (ECG).

Image by Lecturio.

Incomplete RBBB and LBBB

A bundle branch block may be considered incomplete if the usual RBBB or LBBB pattern is seen but the QRS duration is 110–119 msec.

Left anterior fascicular block on ECG ECG An electrocardiogram (ECG) is a graphic representation of the electrical activity of the heart plotted against time. Adhesive electrodes are affixed to the skin surface allowing measurement of cardiac impulses from many angles. The ECG provides 3-dimensional information about the conduction system of the heart, the myocardium, and other cardiac structures. Electrocardiogram (ECG)

QRS duration < 120 msec
Left-axis deviation (approximately 45–90 degrees)
R-peak time ≥ 45 msec in lead aVL (measured from the start of the Q wave to the peak of the R wave)
qR complexes in leads I and aVL
rS complexes in leads II, III, and aVF

ECG ECG An electrocardiogram (ECG) is a graphic representation of the electrical activity of the heart plotted against time. Adhesive electrodes are affixed to the skin surface allowing measurement of cardiac impulses from many angles. The ECG provides 3-dimensional information about the conduction system of the heart, the myocardium, and other cardiac structures. Electrocardiogram (ECG) demonstrating left anterior fascicular block:
Here, the axis Axis The second cervical vertebra. Vertebral Column: Anatomy is deviated to –60 degrees and a small Q wave is noted in aVL. The QRS is slightly prolonged, but still < 120 msec.

Image by Lecturio.

Left posterior fascicular block on ECG ECG An electrocardiogram (ECG) is a graphic representation of the electrical activity of the heart plotted against time. Adhesive electrodes are affixed to the skin surface allowing measurement of cardiac impulses from many angles. The ECG provides 3-dimensional information about the conduction system of the heart, the myocardium, and other cardiac structures. Electrocardiogram (ECG)

QRS duration < 120 msec
Right-axis deviation (90–180 degrees)
qR complexes in leads II, III, and aVF
rS complexes in leads I and aVL

ECG ECG An electrocardiogram (ECG) is a graphic representation of the electrical activity of the heart plotted against time. Adhesive electrodes are affixed to the skin surface allowing measurement of cardiac impulses from many angles. The ECG provides 3-dimensional information about the conduction system of the heart, the myocardium, and other cardiac structures. Electrocardiogram (ECG) demonstrating a left posterior fascicular block:
There is right axis Axis The second cervical vertebra. Vertebral Column: Anatomy deviation (+ 100 degrees), small Q waves in II, III, and aVF, rS complexes in I and aVL. The QRS complex QRS complex Electrocardiogram (ECG) duration is also < 120 msec.

Image by Lecturio.

What is right bundle branch block with LAFB?

RBBB + LAFB is the most common of the two patterns. This is due to a single coronary artery blood supply (LAD) to the anterior fascicle. RBBB + LPFB is less common due to a dual blood supply (right and left circumflex arteries), and this combination may be associated with more extensive underlying cardiac pathology.

Is Fascicular block the same as bundle branch block?

Bundle branch block is partial or complete interruption of impulse conduction in a bundle branch; fascicular block is similar interruption in a hemifascicle of the bundle. The 2 disorders often coexist. There are usually no symptoms, but presence of either suggests a heart disorder. Diagnosis is by electrocardiography.

Is left anterior fascicular block the same as left bundle branch block?

Left anterior fascicular block (LAFB) is an abnormal condition of the left ventricle of the heart, related to, but distinguished from, left bundle branch block (LBBB). It is caused by only the left anterior fascicle – one half of the left bundle branch being defective.

Should I worry about left anterior fascicular block?

A cardiac condition called left anterior fascicular block (LAFB), in which scarring occurs in a section of the left ventricle, may not be as benign as currently thought and could increase the likelihood of heart failure, sudden cardiac death or atrial fibrillation.