Atrioventricular block is a heart rhythm disorder that causes the heart to beat more slowly than it should. It’s caused by communication problems within the heart’s electrical conduction system. For some people, the condition doesn’t cause symptoms; for others, it may be life-threatening.
Atrioventricular block is more common in older adults, and is often linked to heart conditions, such as heart attack or coronary artery disease.
Treatments may help to control atrioventricular block, preventing possible complications or even death among people with the most advanced type, third-degree atrioventricular block.
What is atrioventricular block?
Atrioventricular block is the medical term for a slowed heart rate that occurs because of a malfunction with the heart’s electrical system. There are varying degrees of atrioventricular block, some which are so mild they go undetected and some so severe they may be life-threatening.
Electrical impulses that start in the heart’s sinoatrial node (located within the upper right chamber of the heart) keep the heart pumping. The sinoatrial node is connected to the lower chambers of the heart, known as the ventricles, by the electrical conduction system, which includes the atrioventricular node and the His-Purkinje fiber network. In a healthy heart, electrical impulses, which originate in the sinoatrial node, move through the conduction system to reach the ventricles without interruption. But when a person has atrioventricular block, the electrical impulses may be delayed in reaching the ventricles—or they may be blocked altogether.
There are three types of atrioventricular block:
- First-degree atrioventricular block is the mildest form, caused by a slowdown of electrical impulse conduction from the sinoatrial node to the ventricles. It may not cause any noticeable symptoms or need treatment.
- Second-degree atrioventricular block can sometimes cause a more significant delay in the conduction of electrical impulses between the sinoatrial node and the ventricles; it results in an intermittent block of electrical impulses. People are likely to notice symptoms like dizziness or feeling faint.
- Third-degree atrioventricular block results in complete loss of communication between the sinoatrial node and the ventricles. As a result, the electrical impulses from the sinoatrial node fail to control the heart rate, and the ventricles can beat very slowly or not at all. This block in communication typically causes more severe symptoms than second-degree atrioventricular block. In some circumstances, this may lead to passing out or even cardiac arrest—when the heart suddenly stops beating—a life-threatening condition.
What causes atrioventricular block?
Although some people are born with structural abnormalities in their heart that can cause atrioventricular block, most people develop atrioventricular block as they get older.
For those who develop the condition later in life, atrioventricular block may be caused by the conditions or situations below, which interfere with the heart’s electrical activity:
- Coronary artery disease
- Congenital heart defects
- Heart-valve disease
- Heart attack
- Prior heart surgery
- Inflammation or scarring within the heart’s electrical conduction system
- An overactive vagus nerve, which may cause a person’s heart rate to slow or blood pressure to drop, possibly leading to fainting
- Lyme disease, thyroid disease, and certain other medical conditions
- Certain medications, such as digoxin, calcium channel blockers, or beta blockers, which are used to slow down an elevated heart rate (tachycardia)
What are the symptoms of atrioventricular block?
Some people with atrioventricular block, most notably those with first-degree atrioventricular block, may not experience symptoms.
When people with atrioventricular block do notice symptoms, they may experience:
- A slower-than-normal heart rate
- Dizziness, possibly after standing up from a seated or lying-down position
- Chest pain
- Heart palpitations
- Shortness of breath
- Inability to exercise without having symptoms
How is atrioventricular block diagnosed?
People with first-degree atrioventricular block may not realize that they have a heart-related problem and may not seek a diagnosis for the condition. Their atrioventricular block may only be discovered when doctors are trying to diagnose another condition.
People with second- or third-degree atrioventricular block may see their doctor to discuss the symptoms they are experiencing. They may be diagnosed after discussing their medical history, getting a physical examination, and having various diagnostic tests.
Patients should talk about their heart health, including any congenital (or present at birth) defects, diagnosed heart disease, heart attacks, or prior surgeries, as well as any family history of atrioventricular block. As always, it’s important to tell your doctor about any medications you are taking, such as calcium channel blockers, as well as other health conditions they have.
During a physical exam, doctors may notice that patients have a slower-than-normal heart rate (bradycardia) or low blood pressure.
When doctors suspect atrioventricular block, they may recommend the following tests:
- An electrocardiogram, which tracks the heart’s electrical activity. A patient with atrioventricular block won’t have normal heart wave patterns; the study may show other abnormalities associated with atrioventricular block.
- A wearable monitor, such as a Holter monitor or loop monitor, which records the heart’s activity for the hours or days that you wear it. This is useful in detecting atrioventricular block that occurs intermittently, especially if it isn’t present during a doctor visit.
- An echocardiogram, which is an ultrasound that shows images of the heart in motion. This may reveal heart valve or structural heart problems, or the presence of blood clots.
- Imaging tests, such as CT scan or MRI, which allow doctors to identify issues with the heart’s structure or to rule out other conditions.
- Blood tests, which may confirm the presence of Lyme disease, thyroid disease, or other conditions that may cause atrioventricular block.
- In some instances, a stress test (during which an electrocardiogram measures the heart’s activity during exercise) may be recommended, but is not always needed. Doctors may be able to identify atrioventricular block with this test.
How is atrioventricular block treated?
No treatment may be necessary for people who don’t experience symptoms or complications of atrioventricular block.
When treatment is necessary:
- Treating an underlying issue that causes atrioventricular block (such as Lyme disease) may reverse the condition.
- If atrioventricular block is caused by medication (such as calcium channel blockers), the patient may be told to stop taking that medication.
- Doctors may prescribe atropine, a medication that can improve the conduction of electrical signals throughout the heart, increase the heart rate, and improve overall symptoms. In certain instances, doctors may prescribe isoproterenol, dopamine, dobutamine or epinephrine, if atropine does not help to normalize the heart rhythm.
- Temporary cardiac pacing, which provides external electrical stimulation to the heart, may be used to restore a regular heartbeat.
- In some cases, a permanent pacemaker may be implanted.
What is the outlook for people with atrioventricular block?
Some types of atrioventricular block are reversible, particularly when they are caused by underlying conditions. For the types of atrioventricular block that are not reversible, the condition is very treatable with procedures such as pacemaker implantation. Helping the heart rhythm return to a more normal rate should help people manage the condition and avoid symptoms or other severe downstream consequences such as cardiac arrest.
What makes Yale unique in its treatment of atrioventricular block?
“The Yale Cardiac Electrophysiology Program is an internationally recognized center for expertise in the management of arrhythmias, including atrioventricular block,” says Yale Medicine cardiologist James V. Freeman, MD, MPH, MS. “Yale offers state-of-the-art care, incorporating the latest medical and procedural innovations in the field to treat each patient in an individualized way. In addition, our faculty conduct cutting edge research into the underlying mechanisms and optimal treatment strategies for patients with arrhythmias, including atrioventricular block.”