Atrioventricular block (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:

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.

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).

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. 

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.

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.

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.

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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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.

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.