Introduction

Left bundle branch block (LBBB) is a heart rhythm that causes a delay in electrical signals travelling to the left side of the heart. This affects how the heart contracts and pumps blood. Coronary artery disease (CAD), on the other hand, occurs when blood vessels supplying the heart become narrowed by a build-up of plaque, limiting blood flow. When LBBB and CAD occur together, they can worsen heart function and make both diagnosis and treatment more challenging.

What is left bundle branch block (LBBB)?

LBBB is a type of heart rhythm problem where the electrical signals that control the heartbeat are delayed or blocked in the left bundle branch of the heart’s conduction system, leading to inefficient pumping. Doctors usually spot LBBB using a heart test called an ECG, where they look for changes, including a longer time for each beat and unusual patterns in some areas of the heart trace.¹

What is coronary artery disease (CAD)?

Coronary artery disease (CAD) is caused by atherosclerosis, a condition where plaque builds up in the walls of the coronary arteries, restricting blood flow and oxygen to the heart muscle. CAD can lead to chest pain (angina), heart attacks, acute coronary syndrome (ACS), or go unnoticed (silent myocardial ischaemia). If left untreated, it increases the risk of heart failure or sudden cardiac death.²

Pathophysiology

LBBB often develops when reduced blood flow (ischaemia) or physical injury damages the left bundle branch, a key part of your heart’s electrical system. Normally, the impulse travels along the left side of the heart’s septum and activates both lower chambers of the heart (ventricles) in sync. However, in LBBB, the signal detours through the right side first, delaying left-ventricular contraction. This mismatch in timing, known as mechanical dyssynchrony, can reduce the amount of blood your heart pumps and may contribute to symptoms of heart failure.

In CAD, the artery lining becomes damaged by risks such as high blood pressure or high cholesterol. This allows LDL ('bad') cholesterol to build up and trigger inflammation. White blood cells called macrophages then collect the LDL, forming foam cells and fatty streaks. Over time, these develop into fibrous plaques. If a plaque breaks open, it can trigger a heart attack.

Relationship between LBBB and CAD

LBBB frequently appears in people with CAD and often signals more extensive damage to the heart, such as from heart attacks.³ The Framingham Heart Study found that CAD patients with LBBB are at higher risk of heart failure, death from heart-related causes, and sudden cardiac death. When LBBB shows up during an acute coronary event, it acts like a major warning sign on par with the classic ‘’ST-elevation’’ pattern seen in serious heart attacks.

Diagnostic approaches

Diagnosing a heart attack in someone with both LBBB and CAD can be tricky because the usual ECG signs can be masked. That’s why doctors use the Sgarbossa criteria, which give weight to specific ECG patterns: 

• ST elevation ≥1mm in the same direction as the QRS wave (5 points)
• ST depression ≥1mm in leads V1-V3 (3 points)
• ST elevation ≥5mm in the direction opposite the QRS wave (2 points)

A total score of 3 or more suggests an acute heart attack. A modified version with ST elevation more than 25% of the negative QRS increases the diagnosis accuracy to 80%.¹ Other tools include:^5,6

Treatment and management strategies

Treatment aims at two goals: improving blood flow in CAD and helping your heart beat more efficiently with LBBB.

• In an emergency, such as a suspected heart attack, you need immediate treatment to open your blocked artery. This may include angioplasty (PCI) or clot-busting drugs (thrombolysis)
• Long-term care, especially if LBBB causes heart failure symptoms, might include cardiac resynchronization therapy (CRT). This involves a special pacemaker that helps the lower chambers of your heart (your left and right ventricles) beat together, improving how effectively your heart pumps blood all around your body⁴ 
• A newer method called left bundle branch area pacing (LBBAP) has shown promise
  • Trials have shown that LBBAP helped reduce risks of death or hospitalisation for heart failure compared with traditional biventricular pacing across all types of LBBB patients, including those with CAD⁷
  • LBBAP is shown to be associated with a mean weighted difference in left ventricular ejection fraction (LVEF) improvement of 5.78%, and a significant reduction in paced QRS duration compared to BVP. It also has higher echocardiographic response rates with shorter procedural and fluoroscopy times, enhancing its feasibility⁸

Implications for clinical practice

For people with CAD and LBBB, LBBAP may be a better option than traditional CRT. It more closely mimics natural heart activation by pacing near the left bundle branch, which could improve how your heart pumps and reduce hospital visits. Early results are promising, but as of mid‑2025, we still need longer-term studies before it becomes a standard treatment for everyone.

• Alongside device therapies, medicines continue to play a key role:
  • Antiplatelets to thin the blood and prevent clots
  • Statins to lower cholesterol
  • Beta‑blockers to slow the heart rate and lower blood pressure
  • ACE inhibitors to reduce strain on your heart
• In severe CAD, procedures like coronary artery bypass grafting (CABG) may be needed to restore blood flow

Prognosis and clinical outcomes

Unfortunately, having both CAD and LBBB generally leads to worse outcomes. People in this group have nearly three times the risk of dying from heart disease and a 40% greater risk of death compared to CAD patients without LBBB. In certain diagnostic tests, LBBB also increases the chance of dying from any cause by around 50%.¹ These sobering statistics reinforce why aggressive and effective treatment is so important. 

FAQs

Can LBBB occur in CAD patients without a heart attack?

Yes, LBBB can develop in CAD patients due to chronic ischaemia or structural heart changes, even without an acute heart attack.

Does LBBB in CAD always require a pacemaker?

No, a pacemaker like CRT is typically used only if LBBB causes heart failure or significant symptoms.

How does LBBB affect exercise in CAD patients?

LBBB may reduce exercise capacity due to dyssynchronous heart contractions, but effects vary in individuals.

Are there any specific lifestyle modifications recommended for CAD patients with LBBB?

Yes, recommended lifestyle modifications for CAD patients with LBBB include regular exercise, quitting smoking, limiting alcohol, following a heart-friendly diet, and managing blood sugar, blood pressure, cholesterol, and stress levels. These recommendations are derived from general CAD management strategies, as LBBB often coexists with CAD and shares similar risk factors.

Is there a genetic component to developing LBBB in CAD patients?

Yes, there can be a genetic component to developing LBBB. This is particularly seen in some diseases of the conduction system, such as Lev’s disease, which is associated with mutations in genes such as SCN5A.⁹

Summary

LBBB and CAD are interconnected, with LBBB often signaling severe ischaemic damage in CAD, complicating diagnosis and worsening prognosis. 

Effective management involves advanced diagnostics like Sgarbossa criteria, and treatments like CRT and LBBAP, alongside optimal medical therapy. Ongoing research continues to refine these approaches, aiming for improved outcomes in this complex patient population.