Arrhythmias
Second degree heart block
Second 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.
What second degree heart block is
A heart block refers to a delay to the conduction system in the heart, usually in the AV (atrioventricular) node. This node controls the synchronisation of beats being delivered from the atria, the upper chambers, to the ventricles, the lower chambers that do the main pumping. 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.
Heart block is graded by how much of that signal gets through. In first degree block every signal still arrives, simply later than it should. In second degree heart block some of the electrical signals fail to reach the ventricles altogether, so occasionally a heartbeat is skipped because the signal from the atria does not pass through the AV node. In third degree, or complete, heart block no signal gets through at all.
Treatment depends on the type of heart block you are diagnosed with and on the degree to which any symptoms affect your quality of life. Heart block can develop for several reasons, and the causes listed below apply to heart block in general rather than to second degree block alone.
- Some medications and other chemicals that affect the AV node
- Previous heart attacks
- Infections affecting the heart
- General degeneration of the AV node
The two types, Mobitz I and Mobitz II
There are two types of second degree heart block, known as Mobitz type I and Mobitz type II. The difference matters a great deal, because the two behave differently and are managed differently.
Mobitz I is also known as Wenckebach and is the least serious of the two types. Conduction between the atria and ventricles is delayed more and more with each beat, until one of the atrial impulses is not passed on to the ventricles at all, which is what some people would call a skipped beat. With each beat the AV node continues to become fatigued, leading to slower action with each impulse received. Mobitz I usually carries a lower risk of the condition progressing, and close monitoring is often required, although patients are usually free of symptoms.
Mobitz II describes an intermittent failure of conduction between the Bundle of His and the Purkinje fibres, parts of the conduction system located below the AV node. This type of conduction defect is more likely to be due to a structural issue within the conduction system, either from infection or muscular death, whereas Mobitz type I is more likely to be caused by the effects of medicines and other chemicals on the AV node. Sometimes Mobitz II can present itself in a pattern, whereas at other times there may not be a regular relationship between the impulses of the atria and the ventricles.
Mobitz II is a more dangerous condition and can be associated with haemodynamic compromise, meaning the heart struggles to keep blood circulating properly, along with increased symptoms and a higher likelihood of progressing to third degree heart block. There is an increased risk of sudden cardiac death and blackouts. For that reason it is treated far more assertively than Mobitz I.
Symptoms you may notice
Many people with second degree heart block, particularly the Mobitz I type, have no symptoms at all. The block is often picked up on an ECG that was being carried out for an unrelated reason.
Where symptoms do appear, they usually come from the heart beating more slowly than it should, so the body does not receive enough blood and oxygen during certain activities. Common symptoms include the following.
Symptoms tend to be more noticeable, and are taken more seriously, when the block is Mobitz II. Any persistent dizziness or unexplained fainting should always be assessed by a medical professional rather than put down to tiredness.
- Fatigue or reduced energy
- Dizziness or light-headedness
- A sensation of a skipped or missed beat
- Occasional palpitations
- Shortness of breath during activity
- Episodes of fainting or blackouts
How second degree heart block is diagnosed
The diagnosis of heart rhythm 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. A 12 lead ECG records the electrical signals of the heart and can show whether those signals are being delayed or blocked.
Because second degree heart block can come and go, a single recording in clinic may not capture it. Where symptoms are intermittent, Dr Jogiya may recommend longer monitoring using a portable ECG device worn for 24 hours or longer, so the rhythm can be captured at the moment symptoms occur. An echocardiogram may also be used to assess the structure and function of the heart. Together these tests are what show which type of heart block is present, which matters here because Mobitz I and Mobitz II are managed differently.
Once a diagnosis is made, regular ECGs will be conducted to ensure that treatments are successful and effective.
- A 12 lead ECG to record the heart's electrical activity
- An ECG monitor worn for 24 hours or longer to catch intermittent block
- An echocardiogram to assess the structure and function of the heart
How second degree heart block is treated
Treatment depends on which type of second degree heart block is present and on how much any symptoms are affecting you.
For Mobitz I, close monitoring is often all that is required, since patients are usually free of symptoms and the risk of the condition progressing is lower. This form is more likely to be caused by the effects of medicines and other chemicals on the AV node. Patients who do have symptoms respond to treatment with atropine, a medicine given under medical supervision.
Mobitz II requires the insertion of a permanent pacemaker whether the patient experiences any symptoms or not. This is because of the risk of progression to third degree heart block and the risk of sudden cardiac death and blackouts that comes with it.
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 containing the battery and electronics, and one or more thin wires called leads that connect the device to the heart. It continuously monitors the heart's own rhythm and stays inactive while the heart beats normally, delivering a gentle electrical impulse only when the heart rate drops below a safe level.
The procedure is usually carried out under local anaesthetic with light sedation. A small incision is made beneath the collarbone and the leads are guided through a vein into the heart using X-ray imaging for precision, then connected to the pulse generator, which sits beneath the skin of the chest. Most patients return home within a day and recovery is typically straightforward. Follow-up appointments check that the device is working correctly and allow its settings to be adjusted, and many devices can now be monitored remotely.
When to seek help
Call 999 immediately if you or someone with you has chest pain, collapses, or loses consciousness. Do not wait to see whether it settles.
Arrange an assessment if you have repeated dizziness, unexplained fainting, or a persistent feeling of missed beats. Fainting is taken particularly seriously when it happens during physical activity, comes without any warning, occurs alongside palpitations or chest discomfort, or happens in someone already known to have heart disease.
If you have already been diagnosed with second degree heart block and your symptoms change or become more frequent, contact the practice so the rhythm can be reviewed. A change in symptoms can be the first sign that the block has progressed.
Dr Jogiya sees patients with heart rhythm and conduction problems in Kingston and the surrounding area, and will discuss the most appropriate assessment and treatment for 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.
- 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.