Arrhythmias
Bundle branch block
Bundle branch block describes a block in the part of the heart's conduction system known as the bundle branches. These branches carry the electrical impulse from the AV node down to each ventricle, and when one of them is blocked the signal reaches one side of the heart before the other, so the two ventricles no longer contract in step. It is a pattern picked up on an ECG, and mostly it is something monitored rather than actively treated.
What bundle branch block is and what happens in the heart
Every heartbeat begins with an electrical signal generated in a small area of the heart called the sinus node. That signal spreads across the upper chambers, the atria, and then passes through the AV (atrioventricular) node, which controls the synchronisation of beats being delivered from the atria to the ventricles.
The bundle branches are the next stage of that journey. They deliver the conduction impulses from the AV node to each ventricle, left and right, so that both lower chambers are told to contract together.
In bundle branch block, one of those branches carries the impulse more slowly than the other or does not carry it at all. This conduction delay means that one side of the heart receives the impulse before the other, so the contraction in the ventricles is not synchronised. The heart still beats, but the two sides of it are no longer working in step.
- The impulse leaves the AV node and should reach both ventricles together
- A blocked branch delays the signal on one side
- The two ventricles then contract out of step with each other
- In some people this has no effect on the heart's pumping at all, while in others it affects how well the heart functions
Incomplete bundle branch block
There is a bundle branch running to each ventricle, so a block can affect the left side or the right side of the conduction system.
A bundle branch block might also be described as incomplete. In an incomplete block, impulses are sometimes delivered intermittently through the bundle branches and at other times are blocked, so the pattern comes and goes rather than being present on every beat.
Because of that, a single tracing is not always enough. Repeat ECGs or a period of heart monitoring might be required to diagnose the correct type of bundle branch block before any decision is made about treatment.
What causes bundle branch block
Causes for bundle branch block can be varied. Heart blocks in general can occur for a number of reasons, and the bundle branches sit in a part of the conduction system affected both by the health of the heart muscle around it and by some medicines.
One point matters more than the rest. Bundle branch block in patients with chest pain might suggest a risk of an acute heart attack, so this pattern found alongside chest pain is treated as urgent rather than as an incidental finding.
- Heart disease
- Aortic stenosis
- Some medications
- Previous heart attacks
- Structural heart issues such as cardiomyopathies
The symptoms people notice
Bundle branch block does not always make itself felt. It is frequently found on a tracing taken for another reason, and the block on its own may not change how you feel at all.
Where symptoms do appear, they tend to come either from the effect the unsynchronised contraction has on how well the heart is pumping, or from the underlying condition that caused the block in the first place. Among the conduction delays and heart blocks generally, the symptoms described are shortness of breath, palpitations and dizziness. These are not specific to bundle branch block, and having them does not mean a block is the cause, but they are the ones worth raising with Dr Jogiya.
Chest pain sits in a different category. Because bundle branch block in patients with chest pain might suggest a risk of an acute heart attack, chest pain is not a symptom to monitor at home alongside a known bundle branch block. It needs urgent assessment, and the guidance below explains when to call 999.
If you have been told you have a bundle branch block and you begin to notice new breathlessness, blackouts or a change in how your heart feels, report it rather than waiting for the next routine appointment.
- No symptoms at all, with the block found on a tracing taken for another reason
- Shortness of breath
- Palpitations
- Dizziness
- Chest pain, which is a red flag needing urgent assessment rather than a symptom to watch
How bundle branch block is diagnosed
The diagnosis of heart rhythm and conduction issues is usually done through an ECG, or a Holter monitor, which is a prolonged ECG recording, to get an understanding of the heart rhythm over hours or days rather than seconds.
A standard 12 lead ECG is the first test, because bundle branch block shows itself in the way the electrical signal spreads through the ventricles. Where the block is intermittent, a longer ECG monitor gives a far better picture, and repeat tracings may be needed to confirm which type of block is present.
An echocardiogram may also be arranged to look at the heart itself rather than only its wiring. It assesses the structure and function of the heart, which matters here because the causes of bundle branch block include aortic stenosis and cardiomyopathies, and because it shows whether the unsynchronised contraction is affecting how well the heart pumps.
Once a diagnosis is made, regular ECGs will be conducted to ensure that any treatment is successful and effective.
How bundle branch block is treated
Mostly, bundle branch blocks require monitoring with ECGs and heart monitoring rather than an intervention. Where the block is not affecting the function of the heart and is not causing symptoms, watching it carefully over time is the appropriate approach.
If a bundle branch block does affect the function of the heart or increases symptoms, medication can be used to increase cardiac function.
In more serious cases, cardiac resynchronisation therapy (CRT), also described as biventricular pacing, can be used. It is a form of pacing that aims to put both ventricles back into a synchronised rhythm and so improve the heart's function. It is a device implant, and whether it is suitable depends on how much the block is affecting the heart and the degree to which any symptoms affect your quality of life.
Where a bundle branch block sits alongside another condition, such as aortic stenosis or a cardiomyopathy, treating that underlying condition forms part of the plan as well.
When to seek help
Call 999 immediately for chest pain that is severe or does not settle, for pain spreading to the jaw, back or left arm, for sudden breathlessness with sweating or nausea, or if someone collapses or becomes unresponsive. Bundle branch block in patients with chest pain might suggest a risk of an acute heart attack, and that combination should never be left to wait.
Blackouts and unexplained fainting also need same day medical assessment rather than a routine appointment.
For anything less urgent, such as a bundle branch block found on a recent ECG, gradually worsening breathlessness or palpitations that are becoming more frequent, you can contact the practice to arrange an appointment with Dr Jogiya and discuss the right investigations for you.
This page is general information about bundle branch block. It is not a substitute for individual medical advice, which needs a consultation and your own test results.
More in arrhythmias
Related conditions he treats.
- Atrial fibrillationAtrial fibrillation, commonly known as AF, is a condition where the atria, or upper chambers of the heart, fire chaotic electrical impulses. This leads the muscle to quiver, or fibrillate, instead of beat, so the heartbeat becomes irregular and is often faster than normal. It is one of the most common heart rhythm issues and around 1.7 million people in the UK have been diagnosed with it.
- Atrial flutterAtrial flutter is a heart rhythm problem that affects the upper chambers of the heart, known as the atria. Instead of beating at a normal pace, the atria beat rapidly, but in a regular and organised pattern rather than a chaotic one. Because the chambers do not have enough time to fill properly, blood is not pumped efficiently from the top chambers to the bottom chambers, which is what leads to shortness of breath.
- Atrial tachycardiaAtrial tachycardia is a fast heart rhythm that starts in the atria, the two upper chambers of the heart. An electrical signal emerges from another section of the atria and causes a rapid repeating beat, which means the atria beat very fast. It is one form of supraventricular tachycardia, or SVT, and short bouts of it can be common.
- First degree heart blockFirst degree heart block is common, and it can affect anyone at any age. It describes a delay in the electrical signal as it travels from the upper chambers of the heart to the lower chambers, rather than a true blockage. Every signal still gets through, which is why many people notice nothing at all and why the condition is usually diagnosed when testing is being done for something else.
- Second degree heart blockSecond degree heart block is a fault in the heart's electrical wiring, not a blockage in an artery. Some of the electrical signals travelling from the upper chambers of the heart fail to reach the lower chambers, so a heartbeat is occasionally missed. There are two types, known as Mobitz I and Mobitz II, and they are treated very differently.
- Sick sinus syndromeSick sinus syndrome, also called sinus node disease, is a condition where the sinus node, the small area of tissue that acts as the heart's own natural pacemaker, is not functioning properly. Sometimes the node will send an impulse as it should, and sometimes it may not fire an impulse at all, or the impulses may be out of sync. Some patients notice symptoms such as palpitations and shortness of breath, and because the node is unreliable rather than permanently stopped, those symptoms often come and go.
- Supraventricular tachycardiaSupraventricular tachycardia, usually shortened to SVT, is a fast heart rhythm that starts above the ventricles, in the upper part of the heart. Symptoms vary widely from one person to another, so some people are very aware of an episode while others barely notice one. Short bouts of SVT can be common, and can usually be treated very easily.
- Tachy brady syndromeTachy brady syndrome is a heart rhythm problem in which the heart rate increases and then decreases spontaneously, without any external influence. Instead of settling at a pace that matches what you are doing, the heart swings between periods of a slow rate and sudden bursts of a fast one. It is closely linked to sinus node disease, and it occurs mostly alongside atrial fibrillation.