Introduction

Left bundle branch block (LBBB) is a conduction abnormality of the electrical impulses in the heart known as the left ventricle.¹ This can be caused by an underlying heart disease, such as heart failure (HF). As indicated by its name, HF is used to describe the decline in heart function, which can reduce the heart’s ability to pump blood to the rest of the body sufficiently.² This condition affects between 1-2% of the population, and can occur after injury to the heart, such as a previous heart attack. HF often progresses acutely or over a long period, and those who have developed LBBB have been found to have an increased risk of cardiac arrest.³ Therefore, appropriate management and early intervention are essential to prevent the disease from progressing and reduce the rates of hospitalisation and mortality. 

Diagnosis of LBBB and Heart Failure

The gold standard investigation for diagnosing LBBB is an electrocardiogram (ECG).⁴ This is a non-invasive test to measure the electrical activity of the heart as it contracts. The electrical trace can be interpreted to diagnose various heart diseases, including LBBB, by examining the heart rate, rhythm, frequency, and wavelengths.⁵ 

Assessment of Heart Failure

Clinical presentation (dyspnea, oedema, fatigue)

The most common symptom reported by HF patients is shortness of breath, particularly when lying down (orthopnea), which is usually accompanied by chest pain, fatigue on exertion, and anorexia.⁶ 

When the heart fails to pump sufficient volumes of blood, this can lead to consequences that can affect the individual. This may cause swelling of the lower limbs (oedema) and congestion in the liver, which is a large contributor to the development of anorexia. 

On examination, patients may have a cough with blood in their sputum due to the blood congestion in the lungs. A clinician may examine the neck for the distention of the jugular vein, which indicates blood congestion in the veins. 

In severe forms of HF, patients may show signs of poor perfusion due to insufficient amounts of blood being pumped through the body. 

These may present as: 

• Low blood pressure 
• Reduced volume of urine 
• Cold extremities 
• Blue fingers or lips (cyanosis) 

Diagnostic Tests

Patients presenting with HF may undergo multiple investigations depending on their presenting symptoms, in order to have a thorough understanding of their prognosis, rule out other underlying diseases, and develop an appropriately tailored management plan.⁶ 

These include, but are not limited to: 

• ECG – may reveal underlying heart abnormalities such as LBBB, arrhythmias, and signs of ventricular dysfunction 
• Chest x-ray – may show signs of blood congestion in the lungs, along with cardiomegaly, the enlargement of the heart 
• Echocardiography – an ultrasound scan of the heart used to assess its function, along with blood flow and volume 
• Computed tomography (CT) – mainly used to investigate causes of HF in younger patients, such as obstruction of the coronary arteries, tumour growth, and cardiac birth defects 
• Blood investigations – liver and kidney profiles, cardiac enzymes (indicate cardiac muscle damage, and full blood count (may indicate underlying cardiac infection) 
• Cardiac magnetic resonance imaging – used to assess the heart in greater detail, particularly in patients with complex heart disease 

Impact of LBBB on Heart Failure

Because LBBB is the delayed conduction of the left ventricular cardiac muscle, there is disrupted synchrony of the contractions of the left and right ventricles, giving rise to the risk of arrhythmias and the reduction in the amount of blood the heart can pump per beat (reduced ejection fraction).^1,7   

Over time, the excessive workload on the left ventricle causes the muscle walls, and sometimes the mitral valve, to remodel (change), and eventually contributing to the development of HF and its associated symptoms. Early management and intervention are imperative to control the progression of the disease and manage the experienced symptoms. 

Medical Management Strategies

Pharmacologic Treatments

First-line management of HF usually involves medications that aim to reduce the load on the heart, control symptoms, and improve the overall heart function. Investigations like echocardiography are used to assess the severity of HF, which allows the clinician to choose the appropriate medications to prescribe.⁸ 

These may include:^6,9,10

• Angiotensin converting enzyme inhibitors (ACEi) and angiotensin receptor blockers (ARBs) – aim to reduce workload on the heart and prevent further remodelling 
• Beta blockers – improve symptoms by slowing down the heart rate, reducing the overall pressure in the heart, and reducing the risk of hospitalisations
• Mineralocorticoid receptor antagonists – block the release of the hormone aldosterone, which causes water retention and raised blood pressure 
• Diuretics – more commonly known as “water tablets” aid with symptoms of oedema and reduce workload on the heart  
• Sodium-glucose transporter 2 (SGLT2) inhibitor – a medication used to control diabetes that has evidence of reducing mortality in patients with HF and diabetes

Those with both LBBB and HF can use similar or other medications in conjunction with the ones mentioned above to specifically target LBBB-related dysfunction, such as:^1,11,12

• ARBs, ACEinhbs and beta blockers – to reduce oxygen demand and workload of the heart and reduce the severity of asynchrony between the ventricles 
• Digoxin is not typically prescribed to treat isolated LBBB, but may be used in patients with arrhythmias and ongoing HF 
• Ivabradine – evidence that this medication can reverse the electrical and mechanical remodelling associated with LBBB and improve disease outcomes 

Device Therapy

Cardiac resynchronisation therapy 

A type of pacemaker that aims to correct the desynchronisation of the ventricles in patients with LBBB and HF and a reduced ejection fraction.¹³

Cardioverter defibrillators 

A device that sits just under the skin to prevent sudden cardiac arrest by monitoring electrical abnormalities in the heart and delivering electrical shocks to restore normal rhythm.¹⁴

Summary

• LBBB is a heart condition where there is a conduction abnormality of the left ventricle 
• Remodelling of the ventricle is caused by loss of synchrony between the left and right ventricles, which can contribute to the development of HF  
• HF is when the heart function declines and is unable to sufficiently pump blood across the body 
• Diagnosis of the two conditions includes ECGs, echocardiograms, and evaluation of symptoms and physical examination 
• Management is mostly pharmacological, with medications aiming to reduce the heart’s workload and improve synchrony between the two sides of the heart 

Other management involves devices that focus on managing the heart rhythm and preventing cardiac arrest