Heart block, also known as atrioventricular (AV) block, is a condition in which the electrical signals that coordinate the heartbeat are slowed down or interrupted as they travel from the upper chambers of the heart to the lower chambers. As a result, the heart may beat more slowly, irregularly, or less efficiently.
Despite its name, heart block does not mean that blood flow is blocked or that the heart suddenly stops. Instead, it refers to a problem with the heart’s electrical communication system. The severity of heart block can range from mild and harmless to serious and potentially life-threatening, depending on how much the signal is delayed or blocked.
How the Heart’s Electrical System Works
Each heartbeat begins with an electrical signal generated in the heart’s natural pacemaker. This signal spreads through the atria, causing them to contract and push blood into the ventricles. The signal then passes through a small electrical gateway between the atria and ventricles before continuing downward.
This brief pause at the gateway is essential. It allows the ventricles enough time to fill with blood before they contract. Heart block occurs when this electrical handoff is delayed too much or fails altogether.
What Happens in Heart Block
In heart block, the electrical signal does not travel normally from the atria to the ventricles. Depending on the degree of delay or interruption, the ventricles may receive signals late, intermittently, or not at all.
When the ventricles beat too slowly, the body may not receive enough blood and oxygen, particularly during activity. This is why symptoms, when present, are often related to reduced blood flow to the brain and other organs.
Symptoms of Heart Block
Many people with mild heart block have no symptoms and feel completely well. More advanced forms, however, can cause noticeable and sometimes alarming symptoms.
Before listing symptoms, it is important to understand that symptom severity does not always correlate perfectly with the degree of block. Some individuals adapt gradually, while others develop symptoms suddenly.
Common symptoms include:
- Fatigue or low energy
- Dizziness or lightheadedness
- Shortness of breath during activity
- Exercise intolerance
- Near-fainting or fainting
- Slow or irregular pulse
In severe cases, heart block can cause sudden loss of consciousness and requires urgent medical attention.
Types of Heart Block
Heart block is classified based on how much the electrical signal is delayed or interrupted. These categories help guide treatment and prognosis.
First-Degree AV Block
In first-degree heart block, all electrical signals reach the ventricles, but they travel more slowly than normal. This form is often discovered incidentally and rarely causes symptoms. In many cases, it does not require treatment.
Second-Degree AV Block
In second-degree heart block, some electrical signals fail to reach the ventricles. As a result, occasional heartbeats are “dropped.”
This type is divided into two forms. In one form, the delay gradually increases until a beat is missed. In the other, signals are suddenly blocked without warning. The second form is more serious and may progress to complete heart block.
Third-Degree (Complete) AV Block
In complete heart block, none of the electrical signals from the atria reach the ventricles. The ventricles generate their own slow backup rhythm, which is often insufficient to meet the body’s needs. This form almost always causes symptoms and requires prompt treatment.
Why Heart Block Develops
Heart block can occur for many reasons. In some people, it is related to aging and gradual wear of the heart’s electrical system. In others, it develops after heart surgery, a heart attack, or inflammation of the heart.
Certain medications can also slow electrical conduction and contribute to heart block. In rare cases, people are born with abnormalities in the heart’s electrical pathways.
Identifying the cause is an important part of management, as some forms of heart block are reversible once the underlying issue is addressed.
How Heart Block Is Diagnosed
Heart block is usually diagnosed with an electrocardiogram, which shows how electrical signals move through the heart. Because heart block can be intermittent, longer-term rhythm monitoring may be needed if symptoms occur sporadically.
Additional tests may be performed to evaluate heart structure, identify reversible causes, or assess the risk of progression.
Treatment Options for Heart Block
Treatment depends on the type of heart block, the presence of symptoms, and the underlying cause.
Mild forms may only require observation and periodic follow-up. If medications are contributing to the problem, adjusting or stopping them may improve conduction.
In more advanced cases, especially when symptoms are present, a pacemaker may be recommended. A pacemaker is a small device implanted under the skin that provides reliable electrical signals to maintain an appropriate heart rate and coordination between the heart chambers.
Pacemaker therapy does not cure the underlying electrical disease, but it effectively restores a safe and stable heart rhythm and greatly improves symptoms and quality of life.
Living With Heart Block
A diagnosis of heart block can be unsettling, particularly when symptoms such as fainting or extreme fatigue are present. With appropriate evaluation and treatment, however, most people can lead active and independent lives.
Regular follow-up, attention to symptoms, and adherence to medical advice are essential components of long-term care.
In Summary
The need for treatment in heart block depends largely on its type and the presence of symptoms. First-degree AV block usually does not require treatment and is often managed with observation alone.
Second-degree AV block type I may not need intervention in many cases, but if it causes symptoms such as dizziness or fainting, a pacemaker may be considered. In contrast, second-degree AV block type II and third-degree (complete) AV block represent more advanced conduction problems. When these forms are not congenital, they most often require pacemaker implantation to ensure a safe and reliable heart rhythm.
Reference: Atrioventricular Block
