A bundle branch block (BBB) is a delay or blockage in the heart’s electrical wiring system. This delay affects the speed at which impulses travel to the lower chambers (ventricles), causing them to contract slightly slower than normal. The condition is often detected incidentally during a routine electrocardiogram (ECG). While this diagnosis can sound alarming, a BBB might not cause noticeable symptoms and frequently does not require specific treatment.
The Heart’s Electrical Wiring
The heart’s rhythm is controlled by an internal electrical system that coordinates muscle contractions. This process begins with the sinoatrial (SA) node, the natural pacemaker, which generates the initial electrical impulse. The signal travels through the upper chambers (atria) and arrives at the atrioventricular (AV) node, where it pauses briefly. This stop allows the atria to finish pumping blood before the signal continues to the ventricles.
The impulse then travels down the bundle of His before dividing into the right bundle branch and the left bundle branch. These branches rapidly deliver the electrical signal to the muscular walls of the right and left ventricles. In a healthy heart, the ventricles receive the impulse almost simultaneously, ensuring a synchronized, efficient contraction. A bundle branch block occurs when one of these pathways is damaged or blocked, slowing the electrical signal delivery to the corresponding ventricle.
How the Blockage Affects Pumping
When a block occurs, the electrical signal must find an alternate, slower route to reach the corresponding lower chamber. Instead of using the dedicated high-speed cable, the impulse spreads through ordinary heart muscle tissue, which conducts electricity much more slowly. This detour causes the ventricle on the side of the block to activate after the unaffected ventricle has already begun to contract.
The result is a desynchronized contraction of the two ventricles, which can reduce the heart’s overall pumping efficiency. On an ECG, this delay is visible as a widening of the QRS complex, representing the time it takes for the ventricles to contract. This asynchronous pumping can make it harder for the heart to effectively circulate blood to the rest of the body.
Left Versus Right Bundle Branch Block
Bundle branch blocks are classified based on which pathway is affected, carrying different implications for health. A right bundle branch block (RBBB) is the more common diagnosis and is often considered benign, particularly in otherwise healthy individuals. RBBB can occur in up to three percent of the general population and frequently requires no specific treatment if no structural heart disease is present.
Conversely, a left bundle branch block (LBBB) is viewed as a more significant finding, as it is less common in a normal heart. The presence of LBBB often signals an underlying structural heart condition, such as heart failure or coronary artery disease. LBBB is found in approximately one-third of patients diagnosed with heart failure, highlighting its association with advanced heart disease.
Because the left ventricle pumps oxygenated blood to the entire body, a delay in its activation can have a greater impact on cardiac function than a delay in the right ventricle. LBBB necessitates a comprehensive workup to determine the extent of any existing heart damage. The distinction between the two types guides the physician’s approach to monitoring and treatment.
Causes, Diagnosis, and Treatment
The development of a bundle branch block is a symptom of damage or stress to the heart muscle or the electrical system. Causes vary, but common factors include long-standing high blood pressure (hypertension), coronary artery disease, and heart attacks. Other conditions, such as inflammation of the heart muscle (myocarditis), heart valve disease, or congenital heart defects, can also lead to the blockage. The risk of developing either type of block increases with age and the presence of underlying heart conditions.
Diagnosis is made definitively using an electrocardiogram (ECG), which captures the heart’s electrical activity and displays the characteristic delay. While most people with a block have no symptoms, some may experience fainting (syncope) or dizziness. Since the block is usually an electrical marker of another problem, treatment focuses on managing the underlying disease that caused the damage.
If a person has RBBB and is otherwise healthy, no treatment for the block is necessary, but regular monitoring may be advised. For patients with LBBB, or those with a block accompanied by significant symptoms, a specialized intervention may be required. In these serious cases, a pacemaker may be implanted to help synchronize the contractions of the ventricles, improving the heart’s overall pumping action.