Overview
Heart block, also called atrioventricular (AV) block, is a condition where electrical signals traveling from your heart’s upper chambers (atria) to lower chambers (ventricles) are delayed or blocked. This happens at the AV node, a small cluster of specialized cells that acts as an electrical relay station between the atria and ventricles.
In a normal heart, electrical impulses generated by the sinus node in the right atrium travel through both atria, causing them to contract. The signal then reaches the AV node, which briefly delays transmission to allow the ventricles time to fill with blood. After this delay, the signal continues through the bundle of His and its branches to the ventricles, causing them to contract and pump blood.
Heart block disrupts this orderly sequence. The condition is classified into three degrees based on severity.
First-degree heart block involves delayed conduction through the AV node. Every electrical signal eventually reaches the ventricles, but it takes longer than normal. This shows up on an ECG as a prolonged PR interval. Most people with first-degree block have no symptoms and don’t need treatment.
Second-degree heart block means some signals fail to reach the ventricles. There are two types. Mobitz Type I (also called Wenckebach) shows progressive lengthening of the PR interval until a beat is dropped entirely, then the pattern repeats. Mobitz Type II involves intermittent dropped beats without progressive PR lengthening. Type II is more serious because it can progress to complete block.
Third-degree or complete heart block occurs when no electrical signals pass from the atria to the ventricles. The chambers beat independently, with the atria maintaining a normal rate controlled by the sinus node while the ventricles beat at their own slower escape rhythm, typically 20-40 beats per minute. This is a serious condition requiring prompt treatment.
Heart block can be temporary or permanent, congenital or acquired. Temporary block might result from medication effects, inflammation, or heart attack, and may resolve when the underlying cause is treated. Permanent block results from irreversible damage to the conduction system and typically requires a pacemaker.
Causes
Heart block develops from various conditions affecting the heart’s electrical conduction system.
Coronary artery disease is a common cause, particularly in older adults. Reduced blood flow to the AV node or conduction pathways damages these structures. Heart attacks can cause temporary or permanent heart block depending on the extent of damage.
Aging naturally affects the conduction system. The specialized cells in the AV node and bundle branches can degenerate or develop scar tissue over time, slowing conduction. This is why heart block becomes more common with advancing age.
Heart valve disease, particularly aortic valve calcification, can affect nearby conduction tissue. The AV node and bundle of His lie close to the heart valves, and disease in these valves can impair electrical conduction.
Cardiomyopathy, or disease of the heart muscle, can affect conduction pathways. Dilated cardiomyopathy, hypertrophic cardiomyopathy, and infiltrative diseases like amyloidosis or sarcoidosis all can cause heart block.
Infections affecting the heart, including endocarditis (infection of heart valves) and myocarditis (inflammation of heart muscle), sometimes damage conduction tissue. Lyme disease is a well-known cause of temporary heart block that usually resolves with antibiotic treatment.
Medications commonly cause heart block, particularly those that slow AV conduction. Beta-blockers, calcium channel blockers, digoxin, and some antiarrhythmic drugs can all cause or worsen heart block. This type is usually reversible when the medication is stopped or reduced.
Electrolyte imbalances, especially high potassium levels, can slow conduction through the AV node. This typically resolves when electrolyte levels normalize.
Congenital heart block is present from birth. Babies born to mothers with certain autoimmune diseases, particularly lupus, have increased risk because maternal antibodies can damage the baby’s developing conduction system. Some congenital heart defects also involve abnormalities in the conduction system.
Heart surgery or cardiac procedures can damage conduction tissue. Valve replacement surgery, particularly aortic valve procedures, carries risk of heart block because the AV node and bundle of His are located near the aortic valve. Catheter ablation procedures for arrhythmias occasionally cause unintended heart block.
Neuromuscular diseases including muscular dystrophy can affect the heart’s electrical system as part of their systemic effects.
Athletic heart syndrome rarely causes first-degree heart block in highly trained athletes. This is considered a normal adaptation to exercise and doesn’t require treatment.
Symptoms
First-degree heart block usually causes no symptoms at all. It’s typically discovered incidentally on an ECG performed for another reason. Your heart rate and rhythm remain normal, and the slight delay in conduction doesn’t affect how your heart pumps.
Second-degree heart block may or may not cause symptoms depending on how many beats are dropped. Mobitz Type I often causes no symptoms, especially if dropped beats are infrequent. When symptoms occur, you might notice occasional skipped beats or a brief pause in your heartbeat. Some people describe feeling a flutter or thump when the heart resumes beating after a dropped beat.
Mobitz Type II more often causes symptoms because it can progress to complete block. You might experience dizziness, lightheadedness, or weakness, particularly during activity. Some people notice fatigue or reduced exercise tolerance.
Complete heart block typically causes significant symptoms because the ventricles beat too slowly to meet your body’s needs. The slow ventricular rate, usually 20-40 beats per minute, provides inadequate blood flow.
Fatigue and weakness are prominent. You feel exhausted with minimal activity because your organs and muscles aren’t receiving enough oxygenated blood. Simple tasks like climbing stairs or carrying groceries become difficult.
Dizziness and lightheadedness occur because insufficient blood reaches your brain. You might feel unsteady or like you might faint. This is particularly noticeable when standing up or during activity.
Fainting (syncope) happens when brain blood flow drops critically low. These episodes, called Stokes-Adams attacks, are sudden and without warning. You might lose consciousness for seconds to minutes. Fainting while standing can lead to injuries from falls.
Shortness of breath develops because your heart can’t pump enough blood to meet your body’s oxygen demands. You might feel breathless with minimal exertion or even at rest.
Chest discomfort can occur, though it’s less common. The heart muscle may not receive adequate blood flow when beating very slowly, particularly during activity.
Confusion or difficulty concentrating sometimes occurs in older adults with complete heart block. Insufficient blood flow to the brain affects cognitive function.
Some people with complete heart block feel their heart beating very slowly in their chest. Others notice irregular beats as the atria and ventricles contract independently of each other.
Diagnosis
Diagnosing heart block begins with your medical history and physical examination. Your doctor asks about symptoms, when they occur, medications you take, and any history of heart disease. During examination, they listen to your heart and check your pulse, which may reveal a slow or irregular rhythm.
An electrocardiogram (ECG) is the primary diagnostic tool. This test records your heart’s electrical activity and clearly shows heart block.
Because heart block can be intermittent, a single ECG might not capture it. Extended monitoring helps diagnose these cases. A Holter monitor records your heart rhythm continuously for 24-48 hours while you go about normal activities. You keep a diary of symptoms, helping correlate them with heart rhythm changes.
Event monitors are worn for longer periods, weeks to months, and record when you activate them or when they detect abnormal rhythms. These are useful if symptoms are infrequent.
An exercise stress test evaluates how your conduction system responds to increased heart rate. In some types of heart block, particularly first-degree block in athletes, the PR interval may normalize with exercise, suggesting the block is benign. Conversely, developing block during exercise is concerning.
An electrophysiology study provides detailed information about your conduction system. Catheters threaded into your heart record electrical signals at various points along the conduction pathway. This precisely locates where block is occurring and how severe it is. The study also helps predict whether second-degree block is likely to progress to complete block.
Blood tests check for reversible causes. Potassium levels, thyroid function, and markers of heart damage or inflammation are evaluated. If Lyme disease is suspected, specific antibodies are measured.
Echocardiography assesses your heart’s structure and pumping function. This identifies underlying heart disease that might be causing or associated with heart block.
If you’ve already fainted or have concerning symptoms, your doctor might admit you for continuous hospital monitoring while determining the cause and severity of your heart block.
Treatment
Treatment depends on the degree of heart block, symptoms, underlying cause, and risk of progression.
First-degree heart block rarely requires treatment. If caused by medication, your doctor might adjust the dose or switch to a different drug, but often no changes are needed. Regular monitoring ensures the block doesn’t progress.
Second-degree Mobitz Type I usually doesn’t require treatment if you have no symptoms. If symptoms occur or if medication is causing the block, adjustments may be made. Pacemaker implantation is occasionally needed if symptoms are significant.
Second-degree Mobitz Type II typically requires a pacemaker even without symptoms because this type frequently progresses to complete block. The risk of sudden progression makes prophylactic pacing prudent.
Complete heart block almost always requires pacemaker implantation. This is the definitive treatment and essentially cures the problem. A pacemaker continuously monitors your heart rhythm and provides electrical pacing when your natural rate drops too low. The device ensures your ventricles beat fast enough to meet your body’s needs.
Temporary pacing may be needed before permanent pacemaker implantation. A temporary pacing wire is inserted through a vein, usually in the neck or groin, and positioned in the right ventricle. This provides emergency pacing until a permanent device can be placed.
In emergency situations with complete heart block causing cardiac arrest, immediate treatment includes CPR, medications to increase heart rate (atropine, dopamine, or epinephrine), and temporary pacing if equipment is available.
Treating reversible causes is important. If heart block results from medication, stopping or reducing the drug often resolves the problem. Lyme disease-related heart block typically improves with antibiotic treatment, though temporary pacing may be needed during recovery. Heart block from acute myocarditis or heart attack sometimes resolves as the acute condition improves.
Electrolyte abnormalities causing heart block require correction. Lowering high potassium levels often restores normal conduction.
For congenital heart block in babies, decisions about pacing depend on symptoms and heart rate. Some children need pacemakers in infancy, while others are monitored closely and receive pacemakers later if symptoms develop or heart rate drops too low.
What Happens If Left Untreated
Consequences of untreated heart block depend entirely on severity.
First-degree heart block requires no treatment and causes no problems if left alone. It may be a marker of underlying heart disease in some people, but the block itself poses no danger.
Untreated second-degree Mobitz Type I rarely causes serious problems. However, symptoms of inadequate heart rate, if present, will continue. The main concern is progression to more severe block, though this happens less commonly with Type I than Type II.
Second-degree Mobitz Type II poses significant risk if untreated. This type can suddenly progress to complete heart block without warning. Sudden complete block can cause fainting or cardiac arrest, potentially while driving or in other dangerous situations.
Complete heart block is dangerous without treatment. The slow ventricular rate can’t sustain normal life. Chronic insufficient blood flow causes progressive fatigue and exercise intolerance that severely limits daily activities.
Fainting episodes from complete heart block risk serious injury from falls. Hitting your head, breaking bones, or being injured in other ways during sudden loss of consciousness can have lasting consequences, particularly in older adults.
Sudden cardiac arrest can occur if the ventricular escape rhythm fails. The ventricles might stop beating entirely, or develop ventricular fibrillation. Without immediate treatment, this is fatal.
Chronic slow heart rate from untreated complete block can lead to heart failure. When the heart can’t pump enough blood for extended periods, it dilates and weakens. This worsens symptoms and complicates treatment.
The psychological impact is significant. Living with unpredictable fainting episodes creates constant anxiety. Fear of losing consciousness prevents you from driving, going out alone, or participating in activities you enjoy.
What to Watch For
If you’ve been diagnosed with heart block, certain symptoms require immediate medical attention.
Fainting or near-fainting episodes are always concerning. If you lose consciousness or come close to it, seek emergency care immediately. This suggests your heart rate has dropped dangerously low.
Severe dizziness where you can’t stand or walk safely needs urgent evaluation. This may indicate inadequate blood flow to your brain from slow heart rate.
New or worsening shortness of breath, particularly if you feel breathless at rest or with minimal activity, should be reported to your doctor promptly.
Chest pain or pressure, especially if severe or accompanied by other symptoms, requires emergency evaluation. While heart block itself doesn’t typically cause chest pain, you could be experiencing a heart attack or other serious condition.
If you notice your heart beating very slowly or irregularly, particularly if it feels different from your baseline, contact your doctor. Changes in heart rhythm patterns might indicate your block is worsening.
Confusion, difficulty thinking clearly, or memory problems in older adults can signal inadequate brain blood flow from slow heart rate and should be evaluated.
If you have a pacemaker for heart block and experience symptoms suggesting it’s not working properly, such as return of dizziness, fatigue, or slow heart rate, contact your doctor immediately.
Before any surgery or medical procedure, inform all healthcare providers that you have heart block. Some medications and anesthetics can worsen the condition.
Potential Risks and Complications
Heart block itself and its treatments carry potential risks.
The primary risk of untreated advanced heart block is sudden cardiac arrest. The ventricular escape rhythm that takes over in complete block is unreliable and can fail, causing your heart to stop beating.
Progressive heart block can develop. First-degree block rarely progresses, but second-degree Type II often advances to complete block. Regular monitoring helps detect progression before dangerous symptoms occur.
Syncope-related injuries from fainting pose immediate danger. Falls can cause head trauma, fractures, and other serious injuries. Losing consciousness while driving, operating machinery, or in other dangerous situations risks harm to yourself and others.
Heart failure can develop from chronic slow heart rates. The heart dilates and weakens when forced to pump at inadequate rates for extended periods.
Pacemaker-related complications, while uncommon, include infection at the device site, bleeding, collapsed lung during lead placement, lead dislodgement, and device malfunction. These risks are generally low, especially with experienced operators, and the benefits of pacing far outweigh the risks in people who need it.
Medication-induced heart block can progress if the causative medication isn’t recognized and discontinued. Always inform doctors about all medications you take.
Diet and Exercise
Lifestyle modifications for heart block focus on general heart health, as there are no specific dietary restrictions that improve conduction.
Exercise recommendations depend on your specific situation. If you have first-degree or asymptomatic second-degree block, normal physical activity is usually fine. However, competitive athletes with second-degree block may need evaluation before continuing high-intensity sports.
If you have symptomatic heart block or complete block without a pacemaker, exercise should be limited until treatment is provided. The slow heart rate can’t increase adequately to meet the demands of physical activity, potentially causing dangerous drops in blood pressure or fainting.
After pacemaker implantation, you’ll have temporary exercise restrictions while the device heals in place, typically 4-6 weeks. After recovery, most people return to all normal activities. The pacemaker increases your heart rate appropriately during exercise, allowing normal physical activity.
Maintain a heart-healthy diet with fruits, vegetables, whole grains, lean proteins, and healthy fats. This supports overall cardiovascular health and helps manage conditions like coronary artery disease that might be contributing to heart block.
Control blood pressure through diet, limiting sodium to less than 2,300 mg daily, or less if your doctor recommends. High blood pressure stresses your cardiovascular system.
Avoid excessive alcohol, which can have toxic effects on heart tissue including conduction pathways.
Stay well-hydrated, particularly if you have symptoms. Dehydration lowers blood pressure and can worsen dizziness and lightheadedness from slow heart rate.
If medications are causing your heart block, discuss dietary interactions with your doctor. For example, grapefruit juice interacts with some calcium channel blockers.
Prevention
Heart block from degenerative changes or congenital causes can’t be prevented. However, you can reduce risk of acquired heart block by addressing underlying conditions.
Control cardiovascular risk factors including high blood pressure, high cholesterol, and diabetes. These conditions contribute to coronary artery disease, which can damage conduction pathways. Maintaining healthy blood pressure and cholesterol levels protects your heart’s electrical system.
Don’t smoke, and if you do, quit. Smoking damages blood vessels and heart tissue, increasing risk of coronary disease that can lead to heart block.
Manage existing heart disease carefully. If you have coronary artery disease, follow your treatment plan, take medications as prescribed, and maintain follow-up appointments. Optimal management reduces risk of heart attacks that could damage conduction tissue.
Take medications as prescribed, but be aware that some can affect heart conduction. Don’t stop medications on your own, but if you develop symptoms suggesting heart block, contact your doctor. Regular monitoring when taking drugs that affect AV conduction helps detect problems early.
Seek prompt treatment for infections that could affect your heart. Lyme disease, if caught and treated early with antibiotics, rarely progresses to heart block. If you develop a tick bite and rash, see your doctor promptly.
If you need heart surgery, discuss heart block risk with your surgeon. Some procedures carry higher risk, and knowing this helps you make informed decisions and ensures appropriate monitoring afterward.
Regular medical checkups allow early detection of heart conditions that might lead to conduction problems. ECGs performed during routine care can identify developing heart block before symptoms appear.
Key Points
- Heart block ranges from a benign finding requiring no treatment to a serious condition needing immediate intervention. The degree of block, not just its presence, determines significance.
- First-degree heart block is common and usually harmless. If discovered on an ECG, don’t be alarmed. Most people live normal lives without any treatment or restrictions.
- Complete heart block is serious and almost always requires a pacemaker. However, with modern pacemaker technology, people with complete block return to completely normal, active lives after device implantation.
- Symptoms guide treatment decisions. Even second-degree block that might not require pacing in someone without symptoms could need treatment if causing dizziness, fatigue, or other problems.
- Pacemakers for heart block are highly effective and safe. The devices are smaller, last longer, and work better than ever before. Recovery is quick, and most people barely notice the device after the initial healing period.
- If you’ve been diagnosed with heart block, work closely with a cardiologist. Regular monitoring ensures the block isn’t progressing and that treatment, if needed, is provided before serious complications develop.
- Heart block caused by reversible conditions can improve or resolve. If medication, electrolyte imbalance, or infection is causing the problem, treating the underlying issue may restore normal conduction.
- Understanding your specific type of heart block is important. Ask your doctor which degree you have, whether it’s stable or likely to progress, and what signs should prompt you to seek immediate care. This knowledge empowers you to manage your condition confidently.
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Reference: Atrioventricular Block
