Heart Block (Atrioventricular Block)
A condition where electrical signals are delayed or blocked as they travel through the heart's conduction system
Quick Facts
- Type: Cardiac Conduction Disorder
- ICD-10: I44
- Prevalence: 1-3% of adults
- Severity: Varies by degree
Overview
Heart block, also known as atrioventricular (AV) block, is a condition where the electrical signals that coordinate heartbeats are delayed or completely blocked as they travel from the heart's upper chambers (atria) to the lower chambers (ventricles). This disruption in the heart's electrical conduction system can cause irregular heart rhythms and affect the heart's ability to pump blood effectively.
The heart's electrical system normally starts with the sinoatrial (SA) node, which generates electrical impulses that travel through the atria, then through the atrioventricular (AV) node, and finally to the ventricles. When this pathway is interrupted or delayed, heart block occurs. The condition is classified into three degrees based on severity, ranging from mild delays to complete blockage of electrical signals.
Heart block can be temporary or permanent, and may be present at birth (congenital) or develop later in life (acquired). While some forms are mild and require only monitoring, others can be life-threatening and require immediate medical intervention, including pacemaker implantation. The prognosis varies significantly depending on the degree of block and underlying causes.
Symptoms
Heart block symptoms vary greatly depending on the degree of blockage and the underlying heart rate. Many people with first-degree heart block have no symptoms, while those with complete heart block may experience severe symptoms requiring emergency treatment.
Common Symptoms
Cardiovascular Symptoms
- Irregular heartbeat or heart palpitations
- Palpitations - feeling of skipped or extra heartbeats
- Fainting or near-fainting episodes
- Peripheral edema - swelling in legs, ankles, or feet
- Bradycardia (slow heart rate below 60 beats per minute)
Systemic Symptoms
- Weight gain due to fluid retention
- Weakness and reduced exercise tolerance
- Fatigue and decreased energy levels
- Confusion or difficulty concentrating
- Cold, sweaty skin
Symptoms by Heart Block Degree
First-Degree Heart Block
- Usually asymptomatic
- May cause mild fatigue in some patients
- Often discovered incidentally on ECG
Second-Degree Heart Block
- Intermittent symptoms due to dropped beats
- Palpitations or sensation of skipped heartbeats
- Mild dizziness or fatigue
- Type II may cause more pronounced symptoms
Third-Degree (Complete) Heart Block
- Severe fatigue and weakness
- Significant shortness of breath
- Fainting or near-fainting
- Chest pain and heart failure symptoms
- May lead to sudden cardiac death without treatment
Causes
Heart block can result from various factors that damage or interfere with the heart's electrical conduction system. Understanding these causes helps in both prevention and treatment planning.
Congenital Causes
- Congenital heart defects: Structural abnormalities present at birth
- Maternal autoimmune conditions: Lupus or Sjögren's syndrome affecting fetal development
- Genetic mutations: Inherited conditions affecting cardiac conduction
- Intrauterine infections: Viral infections during pregnancy
Acquired Causes
Cardiac Conditions
- Coronary artery disease: Reduced blood flow to conduction system
- Myocardial infarction: Heart attack damaging conduction pathways
- Cardiomyopathy: Disease of the heart muscle
- Myocarditis: Inflammation of the heart muscle
- Endocarditis: Infection of heart valves
- Cardiac surgery: Surgical trauma to conduction system
Medications
- Beta-blockers: Metoprolol, atenolol, propranolol
- Calcium channel blockers: Verapamil, diltiazem
- Digoxin: Cardiac glycoside toxicity
- Antiarrhythmic drugs: Class I and III agents
- Lithium: Psychiatric medication
Systemic Conditions
- Electrolyte imbalances: Hyperkalemia, hypomagnesemia
- Hypothyroidism: Underactive thyroid gland
- Lyme disease: Bacterial infection affecting heart
- Sarcoidosis: Inflammatory disease
- Amyloidosis: Protein deposits in heart tissue
Age-Related Degeneration
- Fibrosis of conduction system
- Calcification of cardiac structures
- Idiopathic progressive conduction disease
- Age-related changes in cardiac physiology
Risk Factors
Several factors can increase the likelihood of developing heart block. Some are modifiable through lifestyle changes, while others cannot be changed but should be monitored.
Non-Modifiable Risk Factors
- Age: Risk increases with advancing age, especially after 65
- Gender: Men slightly more affected than women
- Family history: Genetic predisposition to conduction disorders
- Congenital heart disease: Born with structural heart abnormalities
- Previous heart surgery: History of cardiac procedures
Modifiable Risk Factors
- Coronary artery disease: Manageable through lifestyle and medications
- Hypertension: High blood pressure damages heart over time
- Diabetes: Poor glucose control affects heart health
- Smoking: Damages cardiovascular system
- Excessive alcohol consumption: Can lead to cardiomyopathy
- Drug abuse: Cocaine and other stimulants
Medical Risk Factors
- Autoimmune diseases: Lupus, rheumatoid arthritis, scleroderma
- Thyroid disorders: Both hyper- and hypothyroidism
- Sleep apnea: Chronic stress on cardiovascular system
- Chronic kidney disease: Affects electrolyte balance
- Previous myocardial infarction: Scar tissue affecting conduction
Medication-Related Risk Factors
- Multiple cardiac medications used simultaneously
- High doses of rate-controlling medications
- Drug interactions affecting cardiac conduction
- Inadequate monitoring of medication levels
Diagnosis
Diagnosing heart block requires careful evaluation of symptoms, physical examination, and specialized cardiac testing. Early detection is crucial for determining appropriate treatment and preventing complications.
Clinical Assessment
- Medical history: Symptoms, medication use, family history
- Physical examination: Heart rate, blood pressure, signs of heart failure
- Symptom evaluation: Timing, triggers, severity of symptoms
Diagnostic Tests
Electrocardiogram (ECG)
- Primary diagnostic tool for heart block
- Shows PR interval prolongation in first-degree block
- Reveals dropped beats in second-degree block
- Demonstrates AV dissociation in third-degree block
- 12-lead ECG provides comprehensive view
Holter Monitor
- 24-48 hour continuous ECG monitoring
- Captures intermittent conduction abnormalities
- Correlates symptoms with rhythm disturbances
- Evaluates heart rate variability
Event Monitor
- Extended monitoring for weeks to months
- Patient-activated during symptoms
- Useful for infrequent episodes
- Implantable loop recorders for long-term monitoring
Additional Tests
- Echocardiogram: Assesses heart structure and function
- Exercise stress test: Evaluates conduction during activity
- Electrophysiology study: Detailed assessment of conduction system
- Blood tests: Electrolytes, thyroid function, drug levels
Classification of Heart Block
- First-degree: PR interval >200 ms, all beats conducted
- Second-degree Type I (Wenckebach): Progressive PR prolongation
- Second-degree Type II: Fixed PR with intermittent dropped beats
- Third-degree (Complete): No AV conduction, AV dissociation
Treatment Options
Treatment for heart block depends on the degree of blockage, symptoms, and underlying causes. Options range from observation to permanent pacemaker implantation.
First-Degree Heart Block
- Observation: Regular monitoring with annual ECGs
- Medication review: Assess need for rate-controlling drugs
- Lifestyle modifications: Heart-healthy diet and exercise
- Treat underlying conditions: Manage hypertension, diabetes
Second-Degree Heart Block
Type I (Wenckebach)
- Often asymptomatic and requires only monitoring
- Review and adjust medications if symptomatic
- Consider pacemaker if symptoms persist
Type II
- Higher risk of progression to complete block
- Pacemaker recommended even if asymptomatic
- Urgent evaluation and monitoring
Third-Degree (Complete) Heart Block
- Permanent pacemaker: Standard treatment for most patients
- Temporary pacing: Emergency stabilization
- Immediate hospitalization: For hemodynamically unstable patients
Pacemaker Therapy
Types of Pacemakers
- Single-chamber: Paces ventricles only
- Dual-chamber: Paces both atria and ventricles
- Biventricular: For heart failure with conduction delay
- Rate-responsive: Adjusts rate based on activity
Pacemaker Indications
- Symptomatic bradycardia due to heart block
- Second-degree Type II heart block
- Complete heart block
- Chronotropic incompetence
Medication Management
- Discontinue offending drugs: Beta-blockers, calcium channel blockers
- Atropine: Temporary treatment for acute bradycardia
- Isoproterenol: Bridge therapy before pacemaker
- Treat underlying conditions: Thyroid disorders, electrolyte imbalances
Emergency Treatment
- Transcutaneous pacing: External temporary pacing
- Transvenous pacing: Internal temporary pacing
- Pharmacologic support: Atropine, dopamine, epinephrine
- Fluid resuscitation: If hypotensive
Prevention
While some causes of heart block cannot be prevented, many risk factors can be managed through lifestyle modifications and proper medical care.
Cardiovascular Health
- Control blood pressure: Maintain below 130/80 mmHg
- Manage cholesterol: Keep LDL below target levels
- Diabetes control: Maintain HbA1c below 7% for most patients
- Regular exercise: 150 minutes moderate activity weekly
- Heart-healthy diet: Mediterranean or DASH diet patterns
Lifestyle Modifications
- Smoking cessation: Quit smoking and avoid secondhand smoke
- Limit alcohol: No more than 1-2 drinks per day
- Maintain healthy weight: BMI 18.5-24.9
- Stress management: Practice relaxation techniques
- Adequate sleep: 7-9 hours per night
Medical Management
- Regular check-ups: Monitor cardiovascular risk factors
- Medication compliance: Take prescribed medications as directed
- Drug monitoring: Regular monitoring of cardiac medications
- Infection prevention: Vaccinations, dental hygiene
Specific Prevention Strategies
- Prevent coronary artery disease: Primary prevention in high-risk patients
- Manage autoimmune conditions: Proper treatment of lupus, RA
- Avoid cardiotoxic substances: Cocaine, excessive alcohol
- Monitor thyroid function: Regular screening in at-risk patients
When to See a Doctor
Recognizing when heart block symptoms require medical attention can be life-saving. Some situations require immediate emergency care, while others warrant prompt but non-urgent evaluation.
Seek Emergency Care (Call 911) If You Experience:
- Fainting or loss of consciousness
- Severe chest pain or pressure
- Severe shortness of breath at rest
- Heart rate below 40 beats per minute
- Signs of heart failure (severe swelling, inability to lie flat)
- Confusion or altered mental status
- Prolonged dizziness with chest pain
Schedule Urgent Medical Evaluation For:
- New onset of heart palpitations
- Unexplained fatigue or weakness
- Dizziness or lightheadedness with activity
- Shortness of breath with normal activities
- Swelling in legs, ankles, or feet
- Near-fainting episodes
- Irregular or very slow heartbeat
Routine Follow-up Needed For:
- Known first-degree heart block (annual monitoring)
- Pacemaker check-ups (every 3-6 months)
- Medication adjustments affecting heart rate
- New cardiac symptoms in high-risk patients
Special Considerations
- Elderly patients: May have atypical symptoms
- Diabetic patients: May not feel typical chest pain
- Athletes: Bradycardia may be normal
- Pregnancy: Heart block can affect fetal development
Before Your Appointment
- Document symptoms: timing, triggers, duration
- List all medications and supplements
- Prepare family medical history
- Note any recent changes in health
- Bring previous ECGs or cardiac testing results
Frequently Asked Questions
First-degree heart block involves delayed conduction but all beats reach the ventricles. Second-degree involves some beats being blocked (Type I has progressive delay, Type II has fixed delay with dropped beats). Third-degree is complete blockage where atria and ventricles beat independently.
Not all heart block requires a pacemaker. First-degree and Type I second-degree usually need only monitoring. Type II second-degree and third-degree heart block typically require pacemaker implantation, especially if symptoms are present or the heart rate is very slow.
Some cases of heart block can be reversible if caused by medications, electrolyte imbalances, or infections. However, most cases due to structural heart disease or aging are permanent and require ongoing management, often with a pacemaker.
Most people with pacemakers can return to normal activities. Avoid strong magnetic fields (MRI requires special precautions), contact sports that could damage the device, and activities with repetitive arm movements above shoulder height initially. Your cardiologist will provide specific guidelines.
Heart block is primarily diagnosed with an electrocardiogram (ECG) that shows the characteristic patterns of delayed or blocked electrical conduction. Additional monitoring with Holter monitors or event recorders may be needed to capture intermittent blocks.
Third-degree heart block and high-grade second-degree block can potentially cause sudden cardiac death due to extremely slow heart rates or periods of no heartbeat. This is why pacemaker implantation is often recommended even in asymptomatic patients with these conditions.
References
- Kusumoto FM, et al. 2018 ACC/AHA/HRS Guideline on the Evaluation and Management of Patients With Bradycardia and Cardiac Conduction Delay. Circulation. 2019.
- Epstein AE, et al. 2012 ACCF/AHA/HRS Focused Update Incorporated Into the ACCF/AHA/HRS 2008 Guidelines for Device-Based Therapy. Circulation. 2013.
- Brignole M, et al. 2013 ESC Guidelines on cardiac pacing and cardiac resynchronization therapy. European Heart Journal. 2013.
- Barold SS, Hayes DL. Second-degree atrioventricular block: a reappraisal. Mayo Clinic Proceedings. 2001.
- Rosen KM, et al. Chronic heart block in adults. Archives of Internal Medicine. 1973.
- American Heart Association. Conduction Disorders. AHA. 2024.