Heart Block: Causes, Symptoms, and Treatment
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Medically reviewed by Rafle Fernandez, MD
Atrioventricular block (AV block), more commonly referred to as heart block, is a condition in which the electrical signals of the heart either slow or stop entirely while traveling from its top chambers (atria) to the bottom chambers (ventricles).
This article will review the various types of heart blocks and their causes, symptoms, treatment, and much more.
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Types of Heart Block
There are three different types of heart blocks; first-degree, second-degree, and third-degree.
First-degree heart block: Tends to be the most mild form of the condition, often causing no symptoms.
Second-degree heart block: Occurs when only some of the electrical current is moving from the atria to the ventricles. There are two subtypes of second-degree heart block:
Mobitz type I: May be mild or progress to Mobitz type II.
Mobitz type II: This form affects the heart's ability to pump blood normally and may lead to skipped or irregular heartbeats.
Third-degree heart block: The electrical current does not make it to the heart's lower chambers, leading to very weak pumping of the blood from the ventricles to the rest of the body. This type of heart block is a medical emergency.
People may also be born with heart block, known as congenital heart block.
Symptoms of Heart Blocks
Heart block symptoms tend to vary according to the degree of the electrical disturbance. Many with first-degree heart block don't experience any symptoms and are found to have the condition through routine testing, which is also known as an "incidental finding." Symptoms of second- or third-degree heart block can include but are not limited to:
Weakness and/or fatigue
Chest pain
Dizziness
Fainting (syncope) or feeling faint
Heart Block Causes
There are many causes of heart block, some of which are reversible and others which are not. Common causes of heart block include:
Medications: Common blood pressure or heart rate medications such as beta-blockers, calcium channel blockers, and digitalis can lead to heart block
Previous damage to the heart caused by a heart attack, heart surgery, or heart disease
Infections such as Lyme disease
It is important to mention that otherwise, healthy individuals may experience intermittent heart block, especially if the vagus nerve is overstimulated.
How Are Heart Blocks Diagnosed?
A cardiologist can properly diagnose a heart block through a thorough history, physical examination, and appropriate testing. During the physical examination, the healthcare provider will listen to the heart to determine if the heart is beating more slowly than normal (a condition known as bradycardia), if a murmur is present, or if there are other cardiac anomalies.
One useful and non-invasive cardiac test for diagnosing heart block is an electrocardiogram (ECG). An ECG monitors and records the heart's electrical conduction. A healthcare provider may also recommend wearing a Holter monitor, which similarly records the heart's electrical activity, but for longer periods.
A loop recorder may also help diagnose heart block. A loop recorder is a small implantable device that is injected under the skin and can record the heart's electrical activity for several years.
Treatment for Heart Block
If the cause of heart block is due to medications, a simple change in medication may be all that is necessary. In cases of some second-degree and almost all third-degree heart blocks, a pacemaker is necessary to restore proper electrical conduction to the heart. A pacemaker is a small battery-operated device that is implanted under the skin. It implants wire directly into the heart wall with attached sensors. These wires and sensors can restore "normal" electrical conduction to the heart.
Prognosis
If left untreated, heart blocks, especially third-degree heart blocks, can lead to abnormal heart rhythms (arrhythmias), cardiac arrest, heart failure, atrial fibrillation, and even death. This is why it is important to seek medical attention quickly if a heart block is suspected.
Thankfully, with proper management and close follow-up, people with heart blocks can lead relatively full lives. People with pacemakers will have some restrictions, particularly when it comes to contact sports and security measures such as those found in airports. However, with proper education and management, the prognosis of treated heart block is good.
Summary
Heart block is a condition that causes the electrical signals of the heart to slow or stop entirely. Symptoms depend on the severity of the block but can cause heart palpations, fainting, chest pain, and dizziness. Medications or previous heart trauma resulting from cardiac events can also lead to heart block. Severe cases are treated by implanting a pacemaker, but the prognosis for this condition is good.
