Introduction

Have you recently had an electrocardiogram (ECG) and been told that you have something called ‘Left Bundle Branch Block’ (LBBB), even though you feel completely fine? Are you now anxious or confused about what this could mean? The good news is you are not alone, and many others live with a diagnosis of LBBB. 

LBBB is a heart (cardiac) condition that affects the path in which electrical impulses travel across the left side of your heart, causing it to contract and pump blood more slowly than the right side.¹ An ECG is commonly used to detect and monitor the condition. But what happens when you don’t experience any symptoms and feel completely normal? 

In this article, we will explore what the diagnosis of LBBB can mean in the case of someone who does not experience any symptoms (also known as asymptomatic). 

Understanding the pathway of your heart’s electrical impulses

As previously stated, LBBB is a blockage of the electrical impulses on the left side of the heart.² But before we delve into what this really means, we must first understand how these electrical impulses normally travel across the heart. The heart is made up of four chambers split into right and left: the upper two are the atria (further separated into left and right atrium), and the bottom two are known as ventricles (also separated into left and right).³ 

The electrical signal begins in the sinoatrial node (SAN) found in the right atrium.⁴ This then travels down through the upper chambers, which pump blood into the ventricles and reaches the atrioventricular node (AVN). The electrical signal then reaches the bundle of His, where it separates into the right and left bundle branches (LBB).⁵ These bundles are further divided into Purkinje fibres. Imagine these as small, delicate strings woven into the ventricular walls, causing them to contract and pump blood to either the lungs or around the body through the aorta. 

LBBB occurs following a disruption or blockage in the LBB.² This stops the electrical signal from reaching the left ventricle (LV). As the LV is now unable to become electrically excitable and contract, the electrical signal is forced to travel down the right-hand side. After reaching the bundle of His, the electrical signal travels down the right bundle branch and across the interventricular septum (a wall of tissue separating the right and left chambers of the heart) before reaching the LV and finally causing contraction and blood flow through the aorta. 

Although the electrical current eventually reaches its destination, all these steps take a long time. This causes changes to the heart's normal electrical activity and is what’s detected on an ECG by medical professionals and specialists.²

Wouldn't this normally cause symptoms? 

Surprisingly, LBBB doesn't cause noticeable symptoms in everyone, especially in its early stages.¹ Individuals with LBBB may experience nonspecific symptoms like fatigue, shortness of breath or palpitations. However, there is a consensus between researchers and doctors that heart-related diseases (like hypertension and coronary artery disease) cause these symptoms rather than LBBB itself. In a majority of cases, LBBB acts as a clue and suggests an underlying heart condition of structural or degenerative changes.¹

Is LBBB harmless or something to worry about?

Research is quite limited regarding the prognostic significance of asymptomatic patients (whether LBBB might affect your future health and the likelihood of that happening). A study found an association between asymptomatic LBBB and congestive heart failure (CHF), in which your heart is unable to pump enough blood around the body, causing fluid to gather in your lungs and your legs. Even following regular monitoring of the patients involved and adjusting for other potential factors at play, a significant association remained between asymptomatic LBBB and CHF or cardiac-related death.⁶ 

Another group reported the Framingham study, which showed a 50% increase in cardiovascular deaths in people with LBBB within 10 years of receiving their diagnosis. They also commented on a Swedish study of middle-aged people assigned male at birth (AMAB) and noted an increased risk of atrioventricular block (AV block) in those with LBBB than those without.⁷ 

On the other hand, in a study conducted by Delise P et al, a good prognosis was reported in males under the age of 50 with no heart disease, having found no ventricular dysfunction. In the cases of these individuals AMAB, many of them had been practising for competitive sports when their LBBB was picked up incidentally during their pre-participation screening. None of these people experienced any symptoms, but many of them did have a family history of cardiac-related diseases.⁸ 

This then begs the question of whether LBBB is a predictor of cardiac disease or whether said cardiac disease and CHF are caused by asymptomatic LBBB. Unfortunately, further research is required before the relationship between the two can be fully understood.

Management

You might be wondering how you are supposed to manage something that you don't even experience? Or how you are meant to prevent the onset and progression of these associated conditions? Currently, further investigations and imaging can be done to evaluate the degree of LBBB. These include:¹

• ECG (to detect any electrical abnormalities and any worsening of the electrical signals)
• Echocardiography (this creates a moving picture to investigate how well your heart pumps blood)
• Stress imaging (used to assess the volume of blood flow to the heart when at rest and during increased levels of exercise and stress)

Through regular monitoring, doctors and cardiac specialists can protect your heart from worsening over time. However, if the LBBB has worsened and you begin to present with any new symptoms, doctors may consider cardiac resynchronisation therapy (CRT). This is unlikely to be offered to asymptomatic patients.

Living with LBBB

Being told that you have LBBB can be a little unnerving, especially if you haven't experienced any typical symptoms like fatigue or palpitations. It’s important to remember that this doesn't automatically mean that your heart can’t pump blood efficiently or that you have heart disease as of right now. Although caution and caring for your health is advised, there is nothing to stop you from living well.

Doctors may refer you to undergo further investigations to check how well your heart is functioning and closely monitor for any new abnormalities.¹ Even if the disruption to the electrical pathways isn't causing any symptoms, it's important to take care of your heart. You can do this by eating heart-healthy foods and limiting your cholesterol, blood sugar and blood pressure. 

Whilst this might not directly affect the electrical block in your left ventricle, it is a risk factor for further cardiovascular disease. It is also recommended that one be physically active and regularly attend check-ups with doctors and healthcare professionals.

Summary

Left Bundle Branch Block (LBBB) is caused by a blockage or disruption to the heart’s normal electrical pathway on the left side of the heart.¹ This causes a slowed contraction of the LV and leads to symptoms like fatigue and breathlessness.^1,2 However, in some cases, it does not produce any symptoms at all and is detected incidentally on an ECG. Whilst some have claimed no prognostic significance in younger asymptomatic individuals AMAB, others have found a positive correlation between LBBB and cardiac-related conditions or even death.^6-8 

Consequently, further research is needed to definitively conclude the association between LBBB and other heart-related conditions. Generally, advice for those diagnosed with asymptomatic LBBB is to consume heart-healthy foods, undergo physical exercise, and regularly monitor their heart for any changes. 

FAQs

Is LBBB an inherited condition?

No, LBBB isn't considered to be an inherited condition. However, studies have suggested that some genetic mutations can make the onset of bundle branch block more likely.⁷

Will I need a pacemaker?

Most people who are asymptomatic don’t require any treatment. However, if the disease progresses into heart failure and/or worsens over time, it is possible that you may need a pacemaker or cardiac resynchronisation therapy (CRT).¹

Is LBBB considered a type of arrhythmia?

No, an arrhythmia is an abnormality regarding your heart rate or rhythm.⁹  LBBB is caused by a conduction abnormality leading the LV to beat out of sync and slower than the right.^1,2 

Should I wear a heart monitor at home?

No, not usually. Most people with asymptomatic LBBB don’t need continuous monitoring. However, if symptoms like shortness of breath or palpitations develop, doctors and specialists may recommend further testing.