Complete heart block, also known as third-degree heart block, is the most serious type of heart block. It means that there’s a complete separation of electrical activity between the upper chambers (atria) and lower chambers (ventricles) of the heart. Without prompt medical attention, it can be fatal.

A man sits with electrodes attached to his chest while undergoing an EKG to diagnose his heart condition. Share on Pinterest
Getty Images

Your heart has a carefully coordinated electrical system that controls how your heart beats. When the heart’s usual steady flow of electrical signals is interrupted, it can result in potentially dangerous conditions.

One of these conditions is called complete heart block, also known as third-degree heart block.

Complete heart block occurs when electrical impulses that begin in the heart’s upper chambers (atria) don’t travel down to the lower chambers (ventricles). When this happens, the ventricles may not be able to contract properly and pump blood out to the lungs and the rest of the body.

Complete heart block is the most serious type of heart block. First-degree heart block is the mildest and is characterized by a slowdown of electrical impulses from the atria to the ventricles. Second-degree heart block means the impulses occasionally don’t reach the ventricles at all, causing the heart to skip a beat.

Complete heart block is considered a medical emergency. Without prompt medical attention, it can be life threatening.

This article will take a closer look at complete heart block and its causes, symptoms, treatment, and outlook.

Complete heart block has a variety of possible causes. In many cases, it may be caused by some type of heart disease, such as:

Certain medications may also cause complete heart block.

Anti-arrhythmic drugs — which doctors prescribe to treat heart rhythms that are too fast, too slow, or unpredictable — can sometimes trigger first-, second-, or third-degree heart block. Digoxin, a drug commonly used to treat heart failure, is also associated with heart block.

An imbalance of certain electrolytes, such as potassium, can also trigger complete heart block.

In rare cases, a baby may be born with the condition. Congenital third-degree heart block affects about 1 in 20,000 to 25,000 live births, according to the National Organization for Rare Disorders.

What are the risk factors?

Your risk of developing complete heart block increase with age, especially if you have heart-related issues. An estimated 5% to 10% of people over age 70 who have a history of heart disease develop complete heart block.

A 2019 study suggests that people who do not manage their blood pressure or blood glucose levels may also face a greater risk of developing complete heart block.

Some people with complete heart block experience no noticeable symptoms. For others, symptoms may develop gradually or come on suddenly. Some of the more common complete heart block symptoms include:

If any of these symptoms appear suddenly or become severe, call 911. These symptoms are also associated with a heart attack and should be treated as signs of a medical emergency.

To diagnose complete heart block, your doctor must be able to assess the electrical activity in the heart. This is usually done with an electrocardiogram (EKG).

An EKG is a noninvasive test that uses electrodes placed on the chest to record your heart’s electrical activity. It can detect many types of arrhythmias, including complete heart block.

In some cases, though, an EKG may not diagnose the condition. This is because complete heart block can be intermittent, meaning it may come and go.

That’s why diagnosis may also involve heart rhythm monitoring. This is done with a Holter monitor or a patch monitor. These devices continuously monitor and record your heart’s rate and rhythm for 24 hours or longer.

In addition to these diagnostic tests, your doctor will also:

  • review your medical history
  • ask about your symptoms
  • perform a physical examination
  • review the medications you’re currently taking

When complete heart block is first diagnosed, doctors may try to restore healthy electrical activity in the heart with the drug atropine. It’s given in cases of bradycardia, an atypically slow heart rhythm. The drug can sometimes work in cases where complete heart block is triggered by a heart attack or medications.

If complete heart block was caused by a heart attack, a temporary pacemaker may also be used to help restore the heart’s rate and rhythm until the heart muscle has recovered and has healthy blood flow.

In most cases of complete heart block, however, a permanent implantable pacemaker is the only solution. A pacemaker is a small, battery-powered device that sends electrical signals through thin, flexible leads into the heart to maintain a steady rhythm.

If doctors determine that complete heart block is due to a reversible cause, addressing the cause may cause the heart block to go away. For instance, if a medication triggered complete heart block, treatment will likely involve switching to a different medication.

Complete heart block can lead to serious complications, including cardiac arrest — the abrupt halt to heart and lung function. Cardiac arrest can be fatal if not treated immediately.

Because complete heart block causes the heart to work harder to pump blood, one complication is heart failure, a chronic weakening of the heart’s pumping ability.

Complete heart block also means a reduction in blood flow to the brain, which can cause fainting and falls.

The outlook for complete heart block is much more favorable when it’s diagnosed and treated as soon as possible. If complete heart block is treated promptly with a pacemaker or other treatment protocols, the outlook for sustained heart health is promising.

Similarly, if complete heart block can be reversed by changing or eliminating certain medications or correcting an electrolyte imbalance, the outlook is excellent.

However, even with the right treatment, people with complete heart block are at greater risk of heart failure. If you’ve had complete heart block, it’s especially important to work closely with your doctor or cardiologist to make lifestyle changes and to stay on track with any treatment plan.

Complete heart block is the most serious type of heart block. It means that there’s a total block, or separation of electrical activity, between the upper chambers (atria) and lower chambers (ventricles) of the heart. It’s considered a medical emergency and can be fatal if not treated right away.

Complete heart block is often caused by heart disease or a structural issue with the heart. It may also be caused by medications or an electrolyte imbalance. In rare cases, a baby may be born with this condition.

With an accurate diagnosis and timely treatment, you may be able to avoid some of the serious complications that often accompany complete heart block.