Atrioventricular block (AV block)

A cardiac arrhythmia such as AV block is one possible reason for the heart to beat very slowly. AV block is caused by an impairment in the conduction (transmission) of electrical impulses (signals) in the heart. The symptoms may be made worse by any pre-existing conditions that place additional strain on the heart.

At a glance

  • Atrioventricular block (AV block) is caused by an impairment in the conduction (transmission) of electrical impulses in the heart.
  • People with mild AV block (first-degree) and no pre-existing conditions usually have no noticeable symptoms.
  • AV block may also occur temporarily.
  • Symptoms such as heart palpitations, racing heartbeat, weakness, and dizziness, become frequent as of second-degree AV block.
  • As of third-degree AV block, these symptoms also occur during periods of rest.
  • The typical causes of severe forms of AV block include a congenital heart defect, inflammation of the heart muscle, and coronary heart disease (CHD).

Note: The information in this article cannot and should not replace a medical consultation and must not be used for self-diagnosis or treatment.

AV-Block: Ein Arzt begutachtet die Ergebnisse eines EKG, ein Patient liegt auf einer Behandlungsliege.

What is AV block?

There may be many reasons for the heart to beat slowly. Atrioventricular block (AV block) is one of the most common heart rhythm disorders, or cardiac arrhythmias. This disorder is due to an impairment in the transmission of electrical impulses from the atria (upper chambers) to the ventricles (lower chambers) in the heart via the AV node.

The sinus node (SA node) normally regulates cardiac rhythm. As the heart’s natural pacemaker, it generates electrical signals known as impulses in the right upper chamber of the heart (right atrium), which are transmitted in waves and travel to the lower chambers (ventricles) via the AV node. If an AV block is present, it interferes with the transmission of impulses to the ventricles. This disorder is divided into three degrees of severity:

There are three types of AV block (heart block): 1st-degree, 2nd-degree and 3rd-degree.

Grade 1 AV block

The transmission of impulses to the ventricles is delayed. However, the cardiac rhythm is preserved and the heartbeat is not slowed.

Grade 2 AV block

The transmission of impulses is occasionally disrupted. Some impulses no longer reach the ventricles and the heart frequently skips or drops beats.

Grade 3 AV block

Signal transmission is completely blocked (complete AV block) and the impulses no longer reach the ventricles. In this case, substitute impulses in the ventricles prevent the heart from stopping. The heartbeat slows to fewer than 40 beats per minute (bradycardia). With the most severe form of AV block, pacemaker implantation is required.

What are the symptoms of AV block?

The symptoms depend on the severity of the AV block and whether there are any pre-existing conditions that are placing additional strain on the heart or have already caused damage to it. AV block may also occur as a temporary condition.

Grade 1 AV block

People with mild AV block and no pre-existing conditions often do not even realize that they have the disorder, as they frequently have no symptoms.

Grade 2 AV block

Symptoms such as heart palpitations, racing heartbeat, weakness, and dizziness are common. Breathlessness, chest pain, or fainting (syncope) are particularly likely to occur during physical exertion or mental stress.

Grade 3 AV block

The heartbeat is significantly slowed. Symptoms may also occur during periods of rest and are experienced as soon as the disordered heart rhythm occurs. Fluid may build up in the lower legs, causing swelling (edema).

What are the causes of AV block?

AV block may be caused by heart disease and heart defect; hormonal imbalances; side effects of cardiac medication, infectious diseases, auto-immune diseases.

AV block has many different triggers. It is a possible side-effect of some medication, such as certain cardiac agents. In addition, hormone disorders, auto-immune diseases, and infectious diseases (e.g., Lyme disease or borreliosis) can affect the heart’s electrical impulses.

Most severe and permanent cases of AV block are the result of heart diseases, such as congenital heart disease, myocarditis, or coronary heart disease (CHD). Some risk factors for coronary heart disease, such as advanced age, obesity, high blood pressure, or diabetes, represent an additional risk for the occurrence of AV block.

Some athletes experience a mild form of AV block during periods of rest – however, this does not constitute a disorder. 

How common is atrioventricular block?

AV block is one of the more common forms of heart disease. However, it is difficult to estimate how many people are affected.

AV block can be a temporary or permanent condition. While milder degrees of the disorder are more common among young people, older people tend to be affected by a more severe form.

How does AV block progress?

In some cases, a mild form of AV block may disappear when the pulse is elevated during exertion but reappear during periods of rest.

If heart disease is the cause of this impairment, it will usually become a permanent condition.

Sometimes, mild AV block develops into severe AV block.

However, even a severe case of AV block may disappear if, for example, the medication that triggered the issue is stopped.

How is AV block diagnosed?

In some people, AV block is discovered when skipped beats or a very slow heartbeat are detected by a doctor when taking the pulse or listening to the heart. However, an electrocardiogram (ECG) is required as confirmation. By examining an ECG curve, doctors can determine the presence and severity of an AV block. Occasionally, additional specific ECG examinations need to be conducted also, e.g., a stress test or a long-term ECG wearing a portable monitor.

In most cases, further tests are required to ascertain the causes of the AV block and to test whether the heart has been weakened. These include an ultrasound examination of the heart (echocardiogram) or heart catheterization.

How is AV block treated?

The treatment for AV block depends above all on the severity of the symptoms. Frequently, mild AV block requires no treatment at all. In contrast, severe AV block normally requires pacemaker implantation. Medications (e.g., atropine) that accelerate the heartbeat are usually only administered in the event of an emergency.

Pacemakers can be used on a temporary or permanent basis to regulate the heartbeat. However, they cannot cure the disorder itself. For this reason, treatment is also aimed at alleviating the causes.

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What is everyday life like with AV block?

For people with a severe form of AV block, symptoms such as breathlessness and weakness may become a strain. This is often exacerbated by a fear of losing consciousness and life-threatening effects.

The disorder can be life-altering, even with a pacemaker. Sufferers have to become accustomed to regular follow-up examinations and must always carry a pacemaker ID card with them. Some people find it upsetting that the device is visible under the skin.

Where can I find more information?

It is very important for those who require a pacemaker to be provided with sufficient information. Doctors can provide detailed advice and guidance for everyday life. Information is also available from health insurance providers.

In cooperation with the Institute for Quality and Efficiency in Health Care (Institut für Qualität und Wirtschaftlichkeit im Gesundheitswesen) (IQWiG).

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