Arrhythmias
Third degree heart block CHB
Third degree heart block, also called complete heart block, is the most serious form of heart block. The electrical signals fired in the upper chambers of the heart stop reaching the lower chambers altogether, so the two halves of the heart end up beating independently of one another. It needs urgent assessment and, in practice, a permanent pacemaker.
What third degree heart block is
A heart block refers to a delay in the conduction system of the heart, usually at the AV (atrioventricular) node. This node controls the synchronisation of the beats being delivered from the atria, the upper chambers, to the ventricles, the lower chambers. In a patient with a heart block, the impulse being sent to the ventricles might be delayed, or completely out of sync with the signals being received from the atria.
In third degree heart block, or complete heart block, there is an absence of any atrioventricular conduction at all. That leads to a complete dissociation between the impulses being fired in the atria and those in the ventricles. The ventricles therefore have to contract using their own ventricular beats, or using other conduction pathways known as junctional beats.
Because those backup pathways are slower than the heart's normal electrical system, the resulting heart rate is much slower than it should be. Third degree blocks are usually the end point of Mobitz I or Mobitz II second degree blocks, and they signal the failure of the AV node or the ventricular conduction system to perform its necessary tasks.
It is worth saying plainly that the word block does not mean the heart has stopped working, and it does not describe a blockage in an artery. It describes a problem with the electrical signals that control how the heart beats. That distinction matters, because it explains why a treatment such as a pacemaker is effective.
What causes complete heart block
Third degree heart block can be caused by heart attacks, infections, medication, and the general degeneration of the AV node over time.
In some people the heart's electrical system simply changes with age. Other recognised causes include coronary artery disease, a previous heart attack, inflammation affecting the heart muscle, certain medications that influence heart rhythm, and congenital heart conditions present from birth. In some cases no clear cause is identified.
Understanding the underlying cause helps guide treatment and helps determine whether the condition is likely to progress, so the cause is looked into alongside treating the rhythm itself.
Symptoms you may notice
Milder degrees of heart block can go completely unnoticed. Complete heart block is different, and all patients will likely experience symptoms.
These symptoms come from the heart beating far more slowly than the body needs. When the heart rate becomes too slow, the body may not receive enough blood and oxygen, and that tends to show itself most during activity.
Any unexplained fainting, or dizziness that keeps returning, should be assessed by a doctor rather than waited out. Chest pain that is severe, comes on suddenly or does not settle should be treated as an emergency, so call 999.
- Shortness of breath
- Palpitations
- Chest pain
- Dizziness or light-headedness
- Fatigue or reduced energy
- Episodes of fainting
How third degree heart block is diagnosed
The diagnosis of heart rhythm issues is usually made with an ECG, or with a Holter monitor, which is a prolonged ECG recording. An ECG records the electrical signals of the heart and can reveal whether those signals are delayed or blocked. In complete heart block, the atria and the ventricles are beating independently of one another.
If your symptoms come and go, longer monitoring may be recommended using a portable ECG device worn for 24 hours or more, so that the rhythm is captured while you are going about a normal day.
An echocardiogram may also be used to assess the structure and function of the heart and to look for an underlying cause. Once treatment is under way, regular ECGs are carried out to confirm that it is working as it should.
Sometimes another type of heart block can present as third degree block, so it is important to keep monitoring a patient in case a different diagnosis becomes apparent.
How it is treated
Third degree heart block requires immediate treatment. All patients with third degree heart block will require urgent admission for monitoring, and will require a permanent pacemaker to control the conduction between the atria and the ventricles.
A pacemaker is a small device, usually about the size of a matchbox, implanted beneath the skin of the chest. It has a pulse generator, which holds the battery and the electronic circuitry, and one or more thin wires called leads that connect the device to the heart. It monitors the heartbeat continuously and delivers a gentle electrical impulse whenever the heart rate falls below a safe level.
The implant procedure is well established. It is usually carried out under local anaesthetic with light sedation, through a small incision beneath the collarbone, with the leads guided through a vein into the heart using X-ray imaging for precision. Most patients return home within a day.
Modern pacemakers are highly reliable and allow patients to return to normal daily activities. Follow-up appointments check that the device is functioning correctly and allow its settings to be adjusted, and many devices can now be monitored remotely rather than needing frequent hospital visits.
When to seek help
The risk of ventricular standstill, known as asystole, and the risk of sudden cardiac death are much greater with third degree heart block. That is why it is always treated as urgent rather than as something to keep an eye on.
Call 999 if you or someone with you collapses or loses consciousness, has sudden or severe chest pain, or becomes suddenly and severely breathless. Do not wait to see whether it settles.
If you have already been told you have a heart block of any degree, or you are having repeated dizzy spells, fainting or breathlessness that you cannot explain, it is worth arranging an assessment. Dr Jogiya is an expert in arrhythmia treatment and the management of abnormal heart rhythms, and will usually begin with an ECG and a discussion of the symptoms you have noticed.
This page is general information about third degree heart block. It is not a substitute for advice about your own circumstances.
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.
- Bundle branch blockBundle 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.
- 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.