Heart block: Types, causes, symptoms, and risk factors

Heart block, AV bundle, or bundle branch block affects the electrical system of the heart. It is different from coronary artery disease, which affects the heart’s blood vessels.

In heart block, the heart beats irregularly and more slowly than usual, potentially stopping for up to 20 seconds at a time.

This is due to a delay, obstruction, or disruption along the pathway that electrical impulses travel through to make the heart beat. It can result from injury or damage to the heart muscle or heart valves.

Heart block itself does not usually need direct treatment, but related underlying health conditions do.

What is heart block?

[diagram of human heart]
Heart block disrupts the electrical impulses in the heart.

A healthy human heart beats at about 60 to 100 times a minute. A heartbeat is one contraction of the heart muscles, which pushes blood around the body.

Normally, every heart muscle contraction is controlled by electrical signals that travel from the atria, or the upper chambers of the heart, to the ventricles, or the lower chambers.

A partial heart block happens when the electrical impulses are delayed or stopped, preventing the heart from beating regularly.

A complete heart block is when the electrical signals stop completely. The heartbeat will drop to about 40 times per minute.

Even changes to impulses that last only a fraction of a second can cause heart block.

Sometimes, a heart block makes it difficult for the heart to pump blood properly through the circulatory system, so the muscles and organs, including the brain, do not get enough oxygen to function properly.

Heart block typically causes lightheadedness, fainting, and palpitations. Depending on the severity of the heart block, this can be dangerous. For example, a third-degree heart block can worsen pre-existing conditions, such as heart failure. It can cause loss of consciousness and even sudden cardiac arrest. There can also be chest pain.

Coronary heart disease, on the other hand, occurs when a waxy substance, called plaque, builds up in the coronary arteries. It can cause chest pain, known as angina, or heart attack, also called myocardial infarction (MI).

Coronary heart disease: What you need to knowCoronary heart disease: What you need to know
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There are three types of heart block.

First-degree heart block involves minor heartbeat disruptions, such as skipped beats. It is the least serious type of heart block, and it does not generally require treatment.

Second-degree heart block occurs when some electrical signals never reach the heart, causing dropped or skipped beats. The patient may feel dizzy, and they may need a pacemaker. The ventricle may not contract, as the atrial impulse did not reach the ventricles.

Third-degree or complete heart block is when electrical signals do not travel between the upper and lower chambers of the heart. It is more common in patients with heart disease. Without a pacemaker, there is a serious risk of heart attack.

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In a healthy heart, electrical impulses that travel inside a heart muscle instruct it to contract, or beat.
The impulses move along a pathway, from the upper heart chambers, through the atrioventricular (AV) node, to the lower chambers.

Along this pathway is a cluster of cardiac fibers. These are called the bundle of His, the “bundle branch block” or the “AV bundle.” This bundle divides into two branches, the right and left bundles. The bundles conduct the electrical impulses to the heart ventricles. Each ventricle has a branch.

Damage to one of the branch bundles can cause uncoordinated ventricular contractions, and an abnormal heart beat can result.

A blocked signal on the right side of the heart is not usually serious, but a block on the left side can indicate a higher risk of coronary artery disease, or some other heart problem.


If a person has a heart block, they may experience:

slow or irregular heartbeats, or palpitations

shortness of breath

lightheadedness and fainting

pain or discomfort in the chest

difficulty in doing exercise, due to the lack of blood being pumped around the body

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