Bundle Branch Block: Causes and EKG Patterns

Bundle branch block occurs when electrical signals in your heart get delayed or blocked as they travel through the left or right bundle branches of your heart’s conduction system.

EKG patterns for bundle branch block show specific changes: right bundle branch block creates an RSR’ pattern in leads V1-V2, while left bundle branch block produces wide QRS complexes with notched R waves in leads V5-V6.

What Is Bundle Branch Block?

Think of your heart’s electrical system like the wiring in your house. Bundle branch block happens when one of the main electrical pathways gets damaged or blocked.

Your heart has two bundle branches – left and right. These carry electrical signals from the top chambers to the bottom chambers. When one branch doesn’t work properly, the signal takes a detour through the other side.

This detour makes your heartbeat look different on an EKG. The electrical pattern changes in predictable ways that doctors can spot right away.

Types of Bundle Branch Block

Right Bundle Branch Block (RBBB)

Right bundle branch block affects the pathway to your right ventricle. Your left ventricle contracts first, then the signal travels across to activate the right side.

RBBB is often less serious than left bundle branch block. Many people with RBBB live normal lives without symptoms.

Left Bundle Branch Block (LBBB)

Left bundle branch block blocks the pathway to your left ventricle – your heart’s main pumping chamber. The electrical signal must travel around this blockage.

LBBB usually indicates more significant heart problems. It often develops alongside other heart conditions.

Incomplete vs Complete Block

Incomplete bundle branch block means the signal gets through but moves slowly. Complete block means the signal can’t pass through at all.

Complete blocks create more obvious EKG changes. Incomplete blocks show subtler pattern shifts.

Common Causes of Bundle Branch Block

Age-Related Changes

As you get older, your heart’s conduction system naturally wears down. Scar tissue can build up and interfere with electrical signals.

Right bundle branch block becomes more common after age 60. Many older adults develop RBBB without any underlying heart disease.

Heart Disease

Coronary artery disease ranks as a leading cause of bundle branch block. When arteries get blocked, parts of the conduction system don’t get enough oxygen.

Heart attacks can damage bundle branches permanently. The electrical pathways may never fully recover after severe heart muscle damage.

High Blood Pressure

Chronic high blood pressure makes your heart work harder. Over time, this extra strain can damage the electrical system.

Left bundle branch block appears more often in people with long-term hypertension. The left ventricle bears most of the pressure load.

Cardiomyopathy

Cardiomyopathy weakens your heart muscle. As the muscle becomes damaged, the electrical pathways running through it also suffer.

Both genetic and acquired cardiomyopathy can lead to bundle branch blocks. The type depends on which areas get affected most.

Congenital Heart Defects

Some people are born with heart defects that affect the conduction system. Right bundle branch block often appears in children with certain congenital conditions.

Surgical repairs for congenital heart disease can sometimes damage bundle branches accidentally.

EKG Patterns in Bundle Branch Block

Right Bundle Branch Block EKG Features

Right bundle branch block creates a distinctive “rabbit ear” pattern on EKG. You’ll see this most clearly in leads V1 and V2.

The QRS complex gets wider – usually 120 milliseconds or more. Instead of one sharp R wave, you see two peaks that look like rabbit ears.

Lead V1 shows an RSR’ pattern. The second R wave (R’) is usually taller than the first one.

Secondary Changes in RBBB

You’ll also notice T wave changes in RBBB. The T waves typically flip upside down (invert) in leads V1-V3.

These T wave changes happen because the depolarization pattern changed. When electricity flows differently, repolarization changes too.

Left Bundle Branch Block EKG Features

Left bundle branch block makes the QRS complex very wide – often 140 milliseconds or longer. The entire shape changes dramatically.

In leads V5 and V6, you see broad, notched R waves. These leads normally show the left ventricle’s activity most clearly.

Lead V1 often shows a deep, wide S wave. The normal R wave in V1 may disappear completely.

Additional LBBB Changes

LBBB affects more leads than RBBB. You’ll see changes in leads I, aVL, V5, and V6.

The T waves invert in the same leads that show the QRS changes. This creates a pattern doctors call “appropriate discordance.”

How Doctors Diagnose Bundle Branch Block

EKG Interpretation Process

Doctors start by measuring QRS width on your EKG. Normal QRS complexes are less than 100 milliseconds wide.

If your QRS is 120 milliseconds or wider, they look for specific patterns. The shape and location of changes tell them which branch is blocked.

Key Diagnostic Criteria

For RBBB diagnosis, doctors need three things: wide QRS, RSR’ in V1-V2, and inverted T waves in the right chest leads.

LBBB requires wide QRS plus broad R waves in V5-V6 and deep S waves in V1-V2.

Clinical Significance and Symptoms

When Bundle Branch Block Causes Problems

Most people with bundle branch block don’t feel any symptoms. Your heart still pumps blood effectively despite the electrical delay.

Problems arise when bundle branch block develops suddenly or alongside other heart conditions. New LBBB especially warrants immediate attention.

Potential Complications

Complete heart block can develop if both bundle branches fail. This is rare but potentially life-threatening.

Bundle branch block may also make it harder to diagnose heart attacks on EKG. The abnormal baseline pattern can mask changes.

Treatment Options

When No Treatment Is Needed

Isolated right bundle branch block rarely needs treatment. If you have no symptoms and normal heart function, doctors usually just monitor you.

Some people live their entire lives with bundle branch block and never develop problems.

Pacemaker Therapy

Pacemakers help when bundle branch block causes symptoms or progresses to complete heart block.

Special pacemakers called CRT devices can coordinate both ventricles in people with LBBB and heart failure.

Treating Underlying Conditions

Managing the root cause often helps prevent bundle branch block from getting worse. This might include blood pressure control or coronary artery treatment.

Research from the Cleveland Clinic shows that controlling diabetes and cholesterol can slow conduction system damage.

Living with Bundle Branch Block

Regular Monitoring

You’ll need periodic EKGs to track any changes. Your doctor will watch for signs that the block is progressing.

Annual echocardiograms help monitor your heart’s pumping function. This catches problems before they cause symptoms.

Lifestyle Considerations

Most people with bundle branch block can exercise normally. Check with your doctor about any restrictions.

Heart-healthy habits become even more important. Focus on diet, exercise, and stress management to protect your heart.

Advanced EKG Analysis

Fascicular Blocks

The left bundle branch splits into two smaller branches called fascicles. These can block separately from the main bundle.

Left anterior fascicular block causes left axis deviation on EKG. Left posterior fascicular block is less common but causes right axis deviation.

Bifascicular and Trifascicular Blocks

When two of the three main pathways (right bundle, left anterior fascicle, left posterior fascicle) are blocked, it’s called bifascicular block.

Trifascicular block involves all three pathways and often requires pacemaker implantation.

Block Type	QRS Width	Key EKG Features	Clinical Significance
RBBB	≥120 ms	RSR’ in V1-V2	Usually benign
LBBB	≥120 ms	Broad R in V5-V6	Often indicates heart disease
Incomplete RBBB	100-119 ms	RSR’ pattern, narrow QRS	Minimal significance
Incomplete LBBB	100-119 ms	Slight QRS widening	May progress to complete

Conclusion

Bundle branch block represents a disruption in your heart’s electrical system that creates specific, recognizable patterns on EKG. Right bundle branch block typically has a better outlook and may require no treatment, while left bundle branch block often signals underlying heart disease that needs attention.

Understanding these EKG patterns helps you work with your healthcare team to monitor your condition and make informed decisions about treatment. Whether you need a pacemaker, medication, or just regular monitoring depends on your symptoms, heart function, and overall health status.

The key is staying connected with your doctor and following their recommendations for testing and follow-up care. With proper monitoring and treatment when needed, most people with bundle branch block can maintain good quality of life and heart health.

Can bundle branch block go away on its own?

Bundle branch block rarely resolves completely once established. However, incomplete blocks sometimes improve if the underlying cause gets treated early, such as controlling blood pressure or treating heart inflammation.

Is it safe to exercise with bundle branch block?

Most people with isolated bundle branch block can exercise safely without restrictions. Your doctor may recommend an exercise stress test first to ensure your heart responds normally to physical activity.

Does bundle branch block increase stroke risk?

Bundle branch block itself doesn’t directly increase stroke risk. However, the underlying heart conditions that cause bundle branch block – like heart failure or coronary disease – may increase your stroke risk through other mechanisms.

Can medications cause bundle branch block?

Yes, certain medications can slow electrical conduction and cause bundle branch block. These include some heart rhythm drugs, antidepressants, and anti-seizure medications. Always tell your doctor about new EKG changes after starting medications.

How often should I get EKGs with bundle branch block?

The frequency depends on your type of block and symptoms. Stable right bundle branch block might need yearly EKGs, while new or symptomatic left bundle branch block may require monitoring every 3-6 months initially.