Heart block is a type of arrhythmia, which affects the electrical system of the heart.

In heart block, the heart beats irregularly and slower than usual.

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

Heart block is different from coronary heart disease, which occurs when a waxy substance, called plaque, builds up in the coronary arteries. It can cause chest pain, known as angina, or a heart attack, also called a myocardial infarction (MI). There are also certain types of heart attacks that can cause heart block.

Here is what to know about heart block.

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Diagram of a human heart

A healthy, resting 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, electrical signals control every heart muscle contraction and travel from the atria, or the upper chambers of the heart, to the ventricles, or the lower chambers.

A partial heart block happens when there is a delay of the electrical impulses or they move slower than usual.

A complete heart block is when the electrical signals stop completely. The heart rate can drop to about 40 times per minute or slower.

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

Sometimes, 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 can cause lightheadedness, fainting, and palpitations. Depending on the severity of the heart block, it can be a dangerous, life threatening emergency.

There are three types of heart block. These types range from mild to severe.

First degree heart block

This is the mildest form of heart block. It involves minor disruptions to the heartbeat, such as slowing of the electrical signals in the heart, though these signals still reach the ventricles.

First degree heart block is typically asymptomatic. It generally does not cause problems or require treatment.

Second degree heart block

Second degree heart block can come with a slower and sometimes irregular heart rhythm. It occurs when some electrical signals never reach the heart, causing dropped or skipped beats.

Second degree heart block is split into two subtypes:

  • Type 1: This is the less serious form of second degree heart block. It is typically asymptomatic, but in some people, it can cause them to feel lightheaded, dizzy, or faint.
  • Type 2: This is the more serious type of second degree heart block. It can include all of the symptoms as type 1, as well as chest pain and shortness of breath. It requires treatment with a pacemaker to maintain a regular heart rate.

Third degree, or complete, heart block

This is the most severe form of heart block. It occurs when electrical signals do not travel between the upper and lower chambers of the heart. This leads to a slower, more irregular heart rate, which can lead to symptoms, such as:

  • shortness of breath
  • dizziness
  • feeling tired or faint
  • chest pain

Third degree heart block is more common in people with heart disease. It can also worsen preexisting conditions, such as heart failure. It can cause a loss of consciousness and even sudden cardiac arrest.

Third degree heart block requires prompt treatment. Without a pacemaker, there is a serious risk of a heart attack.

Some people are born with heart block. It can happen as a result of a heart defect or a condition the baby’s mother had during pregnancy, known as congenital heart block.

However, it is more common for heart block to develop over time. As a person ages, the nerves that connect the top and bottom of the heart may start to fail.

Other factors may also increase a person’s risk of developing heart block, such as:

  • a heart attack that results in damage to the heart’s electrical system
  • another heart condition, such as coronary artery disease, cardiomyopathy, or heart failure
  • other health conditions, such as diabetes, high blood pressure, or Lyme disease
  • medications that slow the heart’s electrical impulses, such as beta-blockers or calcium channel blockers
  • heart surgery that leaves scar tissue in the heart
  • electrolyte abnormalities that can cause a temporary disruption to the heart’s electrical system
  • degeneration, or aging of the heart’s electrical system

Some people with a milder form of heart block may not experience any symptoms. Others may experience:

  • a slow or irregular heartbeat, or palpitation
  • shortness of breath
  • lightheadedness, dizziness, or fainting
  • chest pain or discomfort
  • difficulty with exercise or exertion due to the heart having trouble pumping blood around the body

People with heart block may appear healthy, but they may have an underlying heart problem.

In the absence of symptoms, a cardiologist typically diagnoses heart block during routine testing for other heart issues.

A diagnosis involves a detailed medical history, physical exam, and certain diagnostic tests.

In the absence of symptoms, a cardiologist typically diagnoses heart block during routine testing for other heart issues.

A diagnosis involves a detailed medical history, physical exam, and certain diagnostic tests.

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An ECG tests for an irregular heartbeat.

An electrocardiogram (ECG) records heart activity and is the most common test doctors use to diagnose heart block. Probes placed on the skin of the chest show the electric impulses through the heart as wave patterns.

Wave abnormalities may indicate heart block. An ECG can also help determine which type of heart block a person has.

A doctor may also use a Holter monitor to help them diagnose heart block. This uses a portable device that a person wears under their clothing that records all of their heartbeats.

The Holter monitor records information about the heart’s electrical activity while the person goes about their normal activities for 1–2 days.

A cardiac event monitor is another type of device that records the heart’s electrical activity. A doctor may use it to diagnose heart block when a person’s symptoms are less frequent.

A person wears the monitor and activates the device when they feel symptoms. A person can use a cardiac event monitor for up to 30 days at a time to monitor their symptoms.

A doctor may also use an implantable loop recorder to diagnose heart block when a person’s symptoms are less frequent. This device continuously monitors a person’s heart rate and rhythm and can record activity for up to 3 years.

Treatment for heart block depends on the type a person has and what is causing it.

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Patients with second or third degree heart block may need a pacemaker.

For first degree heart block, treatment for a person may be as simple as self-monitoring their pulse, attending regular checkups, and knowing when to seek help for more problematic symptoms.

People with second or third degree heart block may need a pacemaker.

A pacemaker is a small, battery-operated device that sends electrical pulses that help keep the heart beating at a regular rate and rhythm. A person can use it temporarily outside of their body or implanted in their chest or abdomen for more permanent use.

A doctor can set many pacemakers to produce an electrical impulse only when needed. Some can sense if the heart stops beating and produces an electrical impulse to restart it. The battery can last many years.

Cell phones, personal stereos, or household appliances do not affect pacemakers, but a person with one should avoid magnetic fields, such as from a magnetic resonance imaging (MRI) scan.

If present, a person must correct any electrolyte abnormalities.

People with heart block may have an increased risk of other types of arrhythmias, such as atrial fibrillation. They may also have a higher risk of heart attack.

A person who has heart block should speak with a doctor if they experience:

  • chest pain
  • dizziness
  • faintness
  • weakness
  • racing or skipped heartbeats
  • shortness of breath
  • swelling in their legs, ankles, or feet

People who have a pacemaker also need to avoid strong magnetic fields. They should not undergo an MRI scan. They also need to seek alternate security screenings in places such as the airport.

Heart block is not always avoidable, but a person can reduce the risk of heart disease by consuming a healthy diet, exercising regularly, minimizing alcohol consumption, and avoiding tobacco.

Most people with heart block can lead normal lives. If a doctor diagnoses a person with heart block, they should work with a cardiologist to develop the right treatment and management plan to stay on top of their heart health.