Introduction

What is left posterior fascicular block and syncope?

The heart has an internal electrical system that facilitates the pumping action that causes the heart to beat. Left posterior fascicular block (LPFB) is a minor cardiac electrical condition where one element of this electrical system called the “left posterior fascicle” is not functioning optimally. Thus, LPFB is an intraventricular conduction delay in which the electrical impulse travelling through the left posterior fascicle is blocked. The heart still beats, however, the electrical signal follows another path.¹ Therefore, there might not be major symptoms, however, it can be detected by investigations like electrocardiogram (ECG) and constant fainting episodes. Fainting is referred to as syncope in medical terms, which is a sudden loss of consciousness due to temporary drop in blood flow to the brain.² Syncope can be caused by a variety of reasons like dehydration, underlying heart condition and orthostatic hypotension, which is the drop in blood pressure when an individual stands up suddenly or changes position.⁴

Clinical importance

If syncope and LPFB occur together, it could indicate an underlying heart condition. LPFB indicates that there is a cardiac impulse conduction issue and it could help to monitor the condition. Syncope indicates that the heart is not pumping blood efficiently, leading to decreased oxygen supply to the brain; this could be caused by irregular heart rhythms, blockage due to atherosclerosis, and structural conditions. If ignored, a combination of LPFB and syncope could cause a sudden cardiac arrest or other serious events. Hence, it is ideal that further testing and monitoring, such as echocardiography, electrophysiological studies, and cardiac monitoring are conducted. 

Understanding LPFB

ECG criteria

In order to diagnose LPFB, it is important to have certain investigations like the electrocardiogram (ECG).³ The ECG helps in detecting the electrical activity of the heart. It is important to take a doctor’s advice for understanding an ECG and not relying on any other information completely; however, certain signs on ECGs could indicate LPFB, such as a right axis deviation or prolonged QRS duration in the absence of any other lung or heart abnormalities. LPFB alone might not be a cause of concern and can be monitored and regulated. 

Aetiology

Typically, problems affecting the electrical conduction system of the heart triggers LPFB. Ischaemic heart disease is another common reason, in which the heart’s tissue, especially the electrical signalling pathways, is damaged by decreased blood flow. Normal conduction can be altered by cardiomyopathies, which are ailments that change the structure or function of the heart muscle. Additionally, the heart’s electrical fibres gradually deteriorate due to degenerative conduction disorder, which is often associated with ageing and raises the risk of conduction blocks, including LPFB.

Clinical significance

LPFB alone is often benign, especially in individuals without symptoms or any underlying heart condition. However, it becomes clinically significant when present with syncope because the combination could suggest an underlying cardiac conduction disorder or structural heart disease.

Evaluation of syncope

Evaluating and assessing syncope begins with thorough physical examination and history taking. It involves looking out for symptoms like nausea or dizziness, triggers like standing up quickly, and time and duration of the episode. Similarly, it is important to note if any triggers cause the symptoms.⁵ Initial investigation includes a comprehensive cardiac history, family history,  an ECG to identify abnormalities like LPFB, measuring blood pressure, and blood tests that include hemoglobin levels and troponin levels. For risk stratification, tools like San Francisco Syncope Rule can aid in identifying patients at higher risk for heart conditions.

Diagnostic tools to evaluate heart condition

Early diagnosis is the key to any disease and treatment to prevent and treat the disorder completely. Early diagnosis could help in early treatment intervention and, thereby, reduce the risk of serious damage and concerns. Ambulatory ECG monitoring is usually the primary step to record heart rhythms over 24/7 to detect cardiac arrhythmias. Individuals with unexplained syncope require constant monitoring to rule out potential cardiac conditions. 

Echocardiography is crucial to assess structural heart disease. 

Management strategies

The key management strategy for managing LPFB is to treat the underlying cause. If ischemic heart disease is identified, management could include antiplatelets, statins, blockers. Structural heart disease could require corrective surgeries and medications for treating heart issues.⁶

Additionally, in terms of intervention versus observation, an asymptomatic LPFB does not require a specific treatment protocol. However, if LPFB is noted in patients with unexplained syncope, especially in the absence of other factors, close monitoring is essential. It could include regular follow-ups, blood work, and ambulatory ECG (Holter) monitoring.⁷ Reviewing individuals medications is crucial as side effects of some drugs taken for other ailments could indirectly slow the conduction rate, thus worsening the situation. Certain drugs that could delay the conduction include beta blockers and calcium channel blockers. 

Moreover, a pacemaker implantation could be considered if LPFB is part of a progressive conduction disorder, especially when accompanied by other blocks such as atrioventricular (AV) block, and associated with syncope. Understanding the symptoms and warning signs could help to provide appropriate treatment at an early stage. Educating people on identifying warning signs and triggers that could exacerbate syncope could be essential for early treatment and improve peoples’ prognosis. It is important to raise awareness of regular body check ups to identify these issues and improve the lifestyle of the individual. 

Summary

Overall, left posterior fascicular block on its own could be asymptomatic; however, if present with syncope, it should be considered for great clinical significance. Timely care is essential for the treatment, thus, early diagnosis, appropriate treatment, follow up, monitoring and awareness among the population is of utmost importance.