Introduction 

When a physician examines an electrocardiogram, also known as an ECG or EKG, the doctor considers other factors beyond just reviewing your heart rate.¹ They also examine the transmission of the electrical signs of the heart. This axis, known as the cardiac axis, can be significant in providing clues about the heart's health. A conduction issue may be identified by one of the hints, namely an axis change called right axis deviation, which helps to identify a conduction abnormality called left posterior fascicular block (LPFB). Even though LPFB is relatively uncommon, identifying the condition is worthwhile, as being aware of it may be an indication of hidden heart disease or the existence of a former heart injury.

The heart’s electrical conduction system

The electrical system synchronises the heart's beating in a regular pattern. It originates in the sinoatrial node, the body's natural pacemaker. The atrioventricular node and bundle of His are then used to pass the signals. The bundle diverges into the right bundle branch and the left bundle branch.^1,2 

The rest of the branches combine with two-minute branches called fascicles. One is the left anterior fascicle, and the other is the left posterior fascicle. The lower back half receives signals in the left ventricle through the left posterior fascicle.² 

When the heart's electrical activity is blocked in the left posterior fascicle, it must take a longer pathway to reach the affected area. This detour alters the timing and direction of electrical transmission in the heart. The operator can detect the difference in an ECG through a doctor.²

Understanding left posterior fascicular block

The left posterior fascicle cannot conduct electrical impulses in Left Posterior Fascicular Block. The impulses are subsequently conveyed via the left anterior fascicle and the heart muscle to the lower back region of the left ventricle. Due to this pathway, the heart's electrical axis shifts towards the right side.¹

Typically, LPFB has no symptoms. However, it may manifest together with other severe diseases, such as coronary artery disease, inferior wall heart attacks, Cardiomyopathy, heart alterations due to high blood pressure, or heart conduction system degenerative disease. It can also develop in cases of infiltrative diseases or post-surgical procedures of the heart.^1,3

Cardiac axis and axis deviation

The cardiac axis is a measurement that indicates the value of the electrical heart impulses. A healthy adult's axis typically ranges between -30 degrees and +90 degrees. When it shifts towards the range of +90 degrees to +180 degrees, it can be referred to as right-axis deviation. When it deviates leftward by 30 degrees through 90 degrees, it is known as left axis deviation ^1,3

In the left posterior fascicle block (LPFB), the electrical signal is directed toward the pathways that lead to the right lower region of the heart, as the left posterior fascicle gets blocked, creating a right-axis deviation.³ This alteration might be one of the significant findings that doctors pay attention to when they diagnose LPFB. Nevertheless, due to other conditions, such as right ventricular enlargement, which also leads to right-axis deviation, they should be excluded before concluding that such a condition exists.

How axis deviation helps identify LPFB

Axis deviation is not only a figure. It is one of the patterns visible on an ECG. In LPFB, deviation with the right axis is apparent-- traditionally, greater than +90 degrees-- and there is no other reason. With this change, there is a tendency for a change in wave pattern in some ECG leads. These patterns show that activation is in a new sequence of the heart muscle.^3,4

LPFB is an infrequently occurring condition; therefore, physicians examine it intimately to eliminate other possible causes of the ECG abnormalities.^1,4 As soon as LPFB is verified, the conclusion becomes a significant addition to the patient's cardiac history and may inform future tests and patient monitoring.

Why LPFB matters for patients

Even though LPFB may not seriously manifest symptoms, it may be a sign of an underlying heart disease that needs care. Doctors may require additional tests upon identifying LPFB, including echocardiography of the heart, stress tests to assess blood flow, and blood tests to check cholesterol and sugar levels. In other cases, an ambulatory ECG can detect irregular heart rhythms.^3,4

LPFB appears in emergency cases; therefore, its detection is also essential. When a patient who has LPFB develops chest pain, the condition may alter the ECG, either mimicking or obscuring a heart attack.^1,4 The awareness of the presence of LPFB assists a doctor in interpreting the ECG more precisely and acting accordingly.

Causes of left posterior fascicular block

Coronary artery disease, particularly following an inferior heart attack, is the most frequent cause of LPFB. Another common cause is degenerative conduction system disease among older adults. Cardiomyopathy, infiltrative diseases such as sarcoidosis or amyloidosis, and some forms of heart surgery can also damage the left posterior fascicle. Aetiology is unidentified in specific individuals, and the results remain unchanged over several decades.^3,4

Symptoms and when to seek medical attention

LPFB is not a prominent symptom in itself. Nevertheless, when it goes hand in hand with other heart issues, one can feel discomfort in the chest, breathlessness, lack of energy, dizziness, fainting, or swollen legs and ankles.^1,3,5 When these symptoms are felt, immediate treatment should be sought, and emergencies such as chest pains or sudden inability to breathe may require faster treatment.

Treatment and follow-up

Overall, LPFB does not provide straightforward treatment for individuals in good health. It revolves around controlling any underlying conditions. This may include medications that help control blood pressure, reduce cholesterol, or other treatments for heart failure, as well as procedural interventions that enhance blood flow in cases of coronary artery disease.^4,5 Lifestyle changes and heart care include eating well, exercising routinely, halting smoking, and managing stress. A pacemaker might be needed when LPFB combines more threatening conduction disturbances.

Living with LPFB

Most patients with LPFB can live active, whole lives, particularly when other heart disease risk factors are adequately controlled. This is possible because early changes in heart rhythm and function are monitored through follow-up visits.^2,4 The most effective way to create long-term well-being is by maintaining a heart-healthy diet and exercise, regularly attending medical examinations, and showing awareness of the condition.

Frequently asked questions

Will LPFB pass away by itself?

LPFB is, in most scenarios, a lasting finding. However, if it is due to a temporary condition, such as an electrolyte imbalance or inflammation, then it may resolve when the underlying issue is addressed.

Does LPFB pose harm?

LPFB is not typically harmful in and of itself. However, it might indicate underlying heart disease, which could be treated and examined.

What distinguishes an LPFB from a bundle branch block?

A bundle branch block affects all of one branch of the heart's conduction system, whereas LPFB causes changes in a small part of the left bundle-branch, the left posterior fascicle.

Does LPFB trigger a heart attack?

LPFB is not related to a heart attack. However, it is present in individuals who have suffered a heart attack before or those with coronary artery disease.

Am I going to need a pacemaker with LPFB?

Isolated LPFB does not usually require a pacemaker. It can only be considered when other issues with the conduction system slow the heartbeats excessively.

Summary

Left Posterior Fascicular Block is an uncommon phenomenon in the heart's electrical system and is most usually detected by the presence of right axis deviation on an electrocardiogram (ECG). Although it seldom produces signs and symptoms, its identification may significantly indicate the presence of already existing heart disease. Emphasis on the identification of LPFB aids in the proper interpretation of ECGs, particularly in emergency cases, and facilitates the early treatment of related heart issues by doctors. Most individuals with LPFB lead normal, active, and productive lives with adequate observation, medical treatment, and a good lifestyle.