Heart Block

Overview

Heart block is a condition in which the electrical signal transmitted from the upper chambers of the heart (atria) to the lower chambers (ventricles) is slowed or completely interrupted. This disruption in conduction prevents the heart from working in a regular and coordinated way.

In a healthy heart, an electrical signal originates in the atria and travels to the ventricles through a specialized conduction point between the two chambers — the AV node. This signal triggers each heartbeat and keeps all four chambers of the heart working in harmony. In heart block, this conduction pathway is damaged. The signal is either delayed, only partially transmitted, or not transmitted at all.

Heart block is also known as AV block (atrioventricular block). The abbreviation "AV" refers to the conduction between the atria and ventricles. It is classified as first, second, or third degree depending on the extent of the damage.

The severity of heart block varies greatly from person to person. In some, there is only a mild conduction delay and no symptoms at all. In others, the heart cannot generate a sufficient rate, leading to serious symptoms or even life-threatening consequences. This is why accurate diagnosis and classification are so important.

Types of Heart Block

Heart block is divided into three main degrees. Each degree represents a different level of conduction disturbance and carries a different clinical significance.

First-Degree AV Block. This is the mildest form. The electrical signal reaches the ventricles from the atria, but is conducted more slowly than normal. Conduction is not interrupted — it is simply delayed. First-degree AV block generally causes no symptoms and is most often discovered incidentally during a routine ECG. On its own it is not a serious condition and usually requires no treatment. However, it can be an early sign of underlying heart disease and is therefore worth monitoring.

Second-Degree AV Block. This is a moderate conduction disturbance. Some electrical signals reach the ventricles, while others do not. This causes irregularity in the heart rhythm. Second-degree AV block is divided into two subtypes.

In Type 1 (also known as Wenckebach block), the conduction time gradually lengthens with each beat until one signal fails to be conducted at all. This cycle then repeats itself. Type 1 is generally more benign and does not always require treatment.

In Type 2, some signals drop suddenly without any preceding prolongation of conduction time. This is a less predictable and more serious pattern. Type 2 can progress to complete heart block over time, which is why a pacemaker is recommended for most patients.

Third-Degree AV Block (Complete Heart Block). This is the most severe form. No signals are conducted from the atria to the ventricles at all. The atria and ventricles work completely independently of each other. The ventricles generate their own very slow and inadequate rhythm, which is not sufficient to meet the body's needs. Third-degree AV block causes serious symptoms and requires urgent treatment. Permanent pacemaker implantation is the standard treatment for this condition.

Symptoms of Heart Block

The symptoms of heart block vary greatly depending on the degree of the condition. First-degree AV block typically causes no symptoms, while complete heart block can lead to serious and life-threatening manifestations.

• Dizziness and lightheadedness. When the heart does not beat fast enough, blood flow to the brain decreases. This causes dizziness and a feeling of lightheadedness. It may be most noticeable when standing up quickly or during physical activity.
• Fainting or near-fainting (Syncope). When the heart rhythm slows significantly or pauses briefly, the brain does not receive enough blood and fainting can occur. Warning signs such as dizziness, nausea, or blacking out of vision usually precede a fainting episode. However, sudden fainting without any warning can also occur.
• Fatigue and weakness. When the heart beats slowly, the body and muscles do not receive enough oxygen. This manifests as persistent fatigue and a noticeable decline in the ability to carry out daily activities.
• Shortness of breath. Shortness of breath may be felt particularly during exercise or with mild physical activity. It is related to a reduction in the heart's pumping capacity.
• Chest discomfort. Some patients may experience a feeling of pressure or discomfort in the chest. This symptom may be more pronounced in those with underlying coronary artery disease.
• Palpitations. Irregularities in heart rhythm can be felt as palpitations. Some patients describe the sensation as the heart "skipping" or "stumbling."
• Reduced exercise capacity. Because the heart rhythm is slow, sufficient blood cannot be pumped during physical activity. This significantly limits physical capacity.

In some people — particularly those with first-degree AV block — there may be no symptoms at all, and the condition is detected only on an ECG.

When to See a Doctor or Go to the Emergency Room

Seek medical attention promptly in the following situations:

• If dizziness or lightheadedness is occurring for the first time or is gradually worsening, an evaluation should be done.
• If fainting or sudden loss of consciousness has occurred, this is an emergency. Call emergency services immediately or go to the nearest emergency room.
• If shortness of breath, chest pain, and dizziness are occurring together, urgent intervention may be needed.
• If you have a known heart condition and new symptoms are developing, contact your doctor.
• If a very slow pulse (below 40-50 beats per minute) is noticed, medical attention should be sought.

Causes of Heart Block

Heart block can result from a wide variety of causes. Some are directly related to the heart, while others stem from general health conditions.

• Age-related changes. The heart's conduction system, including the AV node, can wear down with age. This is the most common cause of heart block in older adults. Fibrosis (stiffening) of the conduction tissue slows or interrupts signal transmission.
• Coronary artery disease and heart attack. Blockage of the arteries supplying the heart reduces blood flow to the AV node. The conduction system can be damaged during or after a heart attack, leading to heart block.
• Cardiac surgery or interventional procedures. The conduction system can be inadvertently damaged during procedures such as open heart surgery, valve repair, or catheter ablation. This is usually temporary but can also lead to permanent heart block.
• Medications. Certain medications slow the signal passing through the AV node. Beta-blockers, calcium channel blockers, digoxin, and some antiarrhythmic drugs have this effect. An excessive dose or an incorrect combination of these medications can cause heart block. Reducing or discontinuing the medication usually resolves the block.
• Lyme disease. Lyme disease, transmitted through tick bites, can affect the heart's conduction system. It should be kept in mind as a potential cause of heart block particularly in younger patients. Heart block usually resolves with treatment of Lyme disease.
• Myocarditis. This is inflammation of the heart muscle. Viral infections, bacteria, or autoimmune conditions can cause myocarditis. The inflammation can affect the conduction system, leading to temporary or permanent heart block.
• Sarcoidosis and amyloidosis. These systemic diseases cause abnormal deposits to accumulate in heart tissue. These deposits can destroy the conduction system and lead to heart block.
• Congenital heart block. Some babies are born with heart block. This may be associated with a structural abnormality of the heart, or it may be related to an autoimmune condition in the mother — particularly lupus.
• Electrolyte imbalance. Excessively high levels of potassium or calcium in the blood can disrupt cardiac conduction. This is more common in people with kidney disease.
• Hypothyroidism. An underactive thyroid gland slows the heart rate and adversely affects the conduction system.

Diagnosis of Heart Block

Heart block is most often diagnosed with an ECG. However, additional tests may be needed to confirm the diagnosis and identify the underlying cause.

• Electrocardiography (ECG). This is the most fundamental test for diagnosing heart block. An ECG records the heart's electrical activity and clearly shows any conduction delay or interruption. It is sufficient to determine the degree and type of heart block. However, an ECG only reflects the rhythm at the moment it is recorded — if symptoms are intermittent, a single ECG may not be enough.
• Holter monitoring. This is a portable device that continuously records the heart rhythm for 24 to 48 hours. It is used in patients with intermittent symptoms to evaluate under what circumstances the heart block occurs and how frequently it is seen.
• Echocardiography. This test uses ultrasound waves to image the heart's structure and function. It is performed not to diagnose heart block itself, but to detect any underlying structural heart disease. It evaluates the strength of the heart muscle and the condition of the valves.
• Blood tests. Electrolyte levels, thyroid function, infection markers, and indicators of autoimmune disease are investigated. If Lyme disease is suspected, a specific blood test is performed.
• Electrophysiology (EP) study. This is a specialized test performed for a detailed evaluation of the heart's conduction system. Thin catheters are guided to the heart through the groin area, and electrical activity is measured along the conduction pathways. It precisely identifies at which level the block is occurring. It is generally performed before a decision is made to implant a pacemaker.
• Exercise stress test. This can be used to evaluate whether symptoms change with exercise. Heart block that improves with exercise and heart block that worsens with exercise carry different clinical meanings.

Treatment of Heart Block

Treatment is determined based on the degree of the block, the underlying cause, and the patient's symptoms. Not all heart block requires treatment.

• Treatment of first-degree AV block. First-degree AV block generally requires no treatment. Regular monitoring is sufficient. If there is an identifiable underlying cause — such as a medication dose, electrolyte imbalance, or thyroid condition — that cause is addressed. During follow-up, progression to second- or third-degree block is monitored.
• Treatment of second-degree AV block. Type 1 second-degree AV block often causes no specific symptoms and does not always require treatment, though close monitoring is recommended. Type 2 second-degree AV block is more serious and carries a risk of progressing to complete heart block, so pacemaker implantation is recommended for most patients.
• Treatment of third-degree (complete) AV block. Permanent pacemaker implantation is the standard treatment. Complete heart block can be an emergency — in such cases, the rhythm is stabilized with a temporary pacemaker before a permanent one is implanted.
• Temporary pacemaker. In acute and reversible situations — such as heart attack, medication toxicity, or Lyme disease — a temporary pacemaker may be used. When the underlying cause resolves, the heart block may resolve on its own.
• Permanent pacemaker. This is the standard treatment for heart block that causes symptoms or carries a risk of progression. A small device is placed in the upper left area of the chest. Thin leads extend from the device to the heart. The pacemaker activates whenever the heart rate drops below a set threshold, preventing it from beating too slowly. Modern pacemakers are very small, reliable, and long-lasting. Battery life is generally between 8 and 12 years. Most patients with a pacemaker can largely continue their normal lives.
• Treating the underlying cause. In medication-induced heart block, the offending drug is discontinued or the dose is reduced. In Lyme disease-related heart block, antibiotic therapy is given. Electrolyte imbalances are corrected. In these situations, the heart block may be reversible and a permanent pacemaker may not be needed.

Living with a Pacemaker

Most patients who receive a pacemaker can largely continue their normal lives. A pacemaker is a life-saving device that, when used correctly, significantly improves quality of life.

• Daily activities. After a pacemaker is implanted, daily activities such as walking, light exercise, travel, and household tasks can generally be carried out safely. For the first few weeks, excessive movement of the arm on the side where the device was implanted is not recommended — your doctor will explain any specific restrictions during this period.
• Electromagnetic interference. Strong magnetic fields can temporarily affect the functioning of a pacemaker. Powerful industrial magnets, MRI machines, and certain medical equipment require caution. However, everyday devices such as mobile phones, computers, microwave ovens, and home appliances are safe for use with modern pacemakers. Always inform medical staff that you have a pacemaker before any medical procedure or imaging.
• Regular check-ups. Regular follow-up is required after a pacemaker is implanted. Check-ups are more frequent in the first year and then typically once or twice a year thereafter. At each visit, proper device function, battery life, and recorded rhythm data are evaluated.
• Carry your identification card. People with a pacemaker are given an identification card containing the device's brand, model, and serial number. Always carry this card with you — it is particularly useful when traveling and during hospital visits.

Preparing for Your Appointment

Seeing a doctor with suspected or confirmed heart block can feel worrying. Going prepared makes both the diagnostic process and treatment planning easier.

What you can do:

• Note when symptoms such as dizziness, fainting, or palpitations began and how often they occur.
• Identify the circumstances in which symptoms arise — at rest or during exercise.
• List all medications you are taking and their doses.
• Mention if you have previously been diagnosed with heart disease, have had cardiac surgery, or have been treated for a rhythm disturbance.
• Share any family history of heart block, sudden cardiac death, or pacemaker implantation.
• Bring any previous ECG results if available.
• Write your questions down in advance.

Questions you can ask your doctor:

• What degree of heart block do I have?
• Do I need treatment?
• Will I need a pacemaker?
• Could my condition progress?
• What activities can I do, and what should I avoid?
• What symptoms should prompt me to go to the emergency room?
• How often do I need to be monitored?
• Could any of my medications be contributing to the heart block?

Your doctor may ask you:

• Have you experienced dizziness or fainting?
• When did the symptoms start and how often do they occur?
• Do they happen at rest or during exercise?
• Have you previously been diagnosed with heart disease or a rhythm disturbance?
• What medications are you taking?
• Is there a family history of heart disease or sudden death?
• Have you recently had a tick bite or been diagnosed with Lyme disease?
• Have you had cardiac surgery or a cardiac procedure recently?