Heart arrhythmias come in many forms, ranging from completely benign to potentially life-threatening. Understanding the different types can help you recognize symptoms and know when to seek medical attention. This post explores the various types of arrhythmias, their characteristics, and their potential impact on your health.
Arrhythmias Originating in the Atria (Upper Chambers)
Sinus Arrhythmias
The sinoatrial (SA) node is your heart’s natural pacemaker. Several types of arrhythmias can occur when there’s an issue with this pacemaker:
Sinus Tachycardia
Sinus tachycardia is a heart rate greater than 100 beats per minute that originates from the sinus node.
Characteristics:
- Regular rhythm with normal P waves
- Heart rate between 100-180 beats per minute
- Normal conduction through the heart
Causes:
- Normal physiological response to exercise, stress, or excitement
- Fever or infection
- Anemia
- Dehydration
- Stimulants like caffeine or medications
- Hyperthyroidism
- Heart failure
Most cases of sinus tachycardia are a normal response to increased physical or emotional demands and resolve when the trigger is removed. However, inappropriate sinus tachycardia (IST) is a condition where the heart beats faster than normal even at rest without an identifiable cause.
Sinus Bradycardia
Sinus bradycardia is a heart rate less than 60 beats per minute that originates from the sinus node.
Characteristics:
- Regular rhythm with normal P waves
- Heart rate less than 60 beats per minute
- Normal conduction through the heart
Causes:
- Normal in athletes and physically fit individuals
- Sleep
- Medications (beta-blockers, calcium channel blockers)
- Hypothyroidism
- Increased intracranial pressure
- Sick sinus syndrome
Sinus bradycardia is often normal and doesn’t require treatment, especially in physically fit individuals. However, if it causes symptoms like fatigue, dizziness, or fainting, medical evaluation is necessary.
Premature Atrial Contractions (PACs)
PACs are extra heartbeats that originate in the atria earlier than the next expected regular beat.
Characteristics:
- Early beat with an abnormal P wave
- Usually followed by a normal heartbeat
- May feel like a “skipped” beat
Causes:
- Often occur in healthy hearts
- Caffeine, alcohol, or nicotine
- Stress or fatigue
- Electrolyte imbalances
- Heart disease
PACs are generally harmless and rarely require treatment unless they cause significant symptoms or occur very frequently.
Supraventricular Tachycardia (SVT)
SVT is a rapid heart rhythm originating above the ventricles, typically causing a sudden increase in heart rate.
Characteristics:
- Regular, rapid heart rate (usually 150-250 beats per minute)
- Sudden onset and offset (“starts and stops suddenly”)
- Normal QRS complexes (narrow complex tachycardia)
Types of SVT include:
- Atrioventricular nodal reentrant tachycardia (AVNRT): The most common type of SVT, involving an extra electrical pathway in or near the AV node
- Atrioventricular reentrant tachycardia (AVRT): Involves an extra electrical pathway between the atria and ventricles
- Atrial tachycardia: Originates from a single spot in the atria
SVT episodes are rarely life-threatening but can cause significant symptoms and may require treatment if frequent or prolonged.
Atrial Flutter
Atrial flutter is characterized by a rapid but organized electrical circuit in the atria.
Characteristics:
- Atrial rate typically 250-350 beats per minute
- Ventricular rate often around 150 beats per minute (due to the AV node blocking some impulses)
- Characteristic “sawtooth” pattern on ECG
- Regular rhythm
Causes:
- Heart disease (coronary artery disease, heart failure)
- Heart valve problems
- Previous heart surgery
- Chronic lung disease
- Alcohol use (especially binge drinking)
- Hyperthyroidism
Atrial flutter requires treatment as it can lead to complications similar to those of atrial fibrillation and can sometimes progress to atrial fibrillation.
Atrial Fibrillation (AFib)
Atrial fibrillation is the most common serious arrhythmia, affecting millions of people worldwide.
Characteristics:
- Chaotic, disorganized electrical activity in the atria
- Irregular ventricular rhythm
- Atrial rates of 300-600 beats per minute
- Absence of distinct P waves on ECG
- Irregular pulse
Types of AFib:
- Paroxysmal: Episodes that come and go, lasting less than 7 days and stopping on their own
- Persistent: Episodes lasting longer than 7 days or requiring intervention to stop
- Long-standing persistent: Continuous AFib lasting more than 12 months
- Permanent: AFib that cannot be restored to normal rhythm or the decision has been made not to try
Causes:
- Age (risk increases with age)
- Heart disease
- High blood pressure
- Diabetes
- Sleep apnea
- Thyroid problems
- Excessive alcohol consumption
- Family history
Atrial fibrillation requires medical attention due to the increased risk of stroke and heart failure.
Arrhythmias Originating in the Ventricles (Lower Chambers)
Premature Ventricular Contractions (PVCs)
PVCs are extra heartbeats that originate in the ventricles earlier than the next expected regular beat.
Characteristics:
- Wide, bizarre-looking QRS complex
- Usually followed by a compensatory pause
- May feel like a “thump” or “flip-flop” in the chest
Causes:
- Often occur in healthy hearts
- Caffeine, alcohol, or nicotine
- Stress or anxiety
- Electrolyte imbalances
- Heart disease
- Certain medications
Occasional PVCs in a healthy heart are usually harmless. However, frequent PVCs or PVCs in someone with heart disease may require evaluation and treatment.
Ventricular Tachycardia (VT)
Ventricular tachycardia is a rapid heart rhythm originating in the ventricles.
Characteristics:
- Rapid heart rate (usually 120-250 beats per minute)
- Wide QRS complexes
- May be regular or slightly irregular
- Can be sustained (lasting more than 30 seconds) or non-sustained
Types:
- Monomorphic VT: QRS complexes have the same shape
- Polymorphic VT: QRS complexes vary in shape
Causes:
- Coronary artery disease
- Previous heart attack with scarring
- Heart failure
- Cardiomyopathy (heart muscle disease)
- Electrolyte abnormalities
- Medication side effects
- Genetic disorders affecting the heart’s electrical system
Ventricular tachycardia is a potentially serious arrhythmia that requires prompt medical attention, as it can lead to ventricular fibrillation.
Ventricular Fibrillation (VFib)
Ventricular fibrillation is a life-threatening emergency where the ventricles quiver instead of contracting effectively.
Characteristics:
- Chaotic, disorganized electrical activity in the ventricles
- No effective pumping of blood
- Irregular, chaotic pattern on ECG
- Leads to cardiac arrest if not treated immediately
Causes:
- Heart attack
- Severe heart disease
- Electrical shock
- Drowning
- Drug toxicity
- Severe electrolyte imbalances
- Genetic disorders affecting the heart’s electrical system
Ventricular fibrillation requires immediate CPR and defibrillation to restore a normal heart rhythm and prevent death.
Conduction Disorders
Conduction disorders occur when the electrical signal that controls the heartbeat is delayed or blocked.
Atrioventricular (AV) Block
AV block occurs when the electrical signal from the atria to the ventricles is delayed or interrupted.
Types:
- First-degree AV block: Delayed conduction through the AV node
- Second-degree AV block:
- Mobitz type I (Wenckebach): Progressive delay in conduction until a beat is dropped
- Mobitz type II: Intermittent failure of conduction without progressive delay
- Third-degree (complete) AV block: Complete failure of conduction from atria to ventricles
Causes:
- Aging of the conduction system
- Heart attack
- Heart surgery
- Medications
- Lyme disease
- Congenital heart defects
The significance and treatment of AV block depend on the type and symptoms. Third-degree AV block often requires a pacemaker.
Bundle Branch Block
Bundle branch blocks occur when there’s a delay or blockage in the specialized conduction pathways (bundle branches) that distribute electrical impulses to the ventricles.
Types:
- Right bundle branch block (RBBB): Delayed activation of the right ventricle
- Left bundle branch block (LBBB): Delayed activation of the left ventricle
Causes:
- Heart attack
- Heart failure
- Congenital heart defects
- Cardiomyopathy
- Aging of the conduction system
Bundle branch blocks may not cause symptoms but can indicate underlying heart disease and may complicate the diagnosis of other heart conditions.
Special Considerations
Arrhythmias in Children
Arrhythmias in children can be different from those in adults:
- Supraventricular tachycardia (SVT) is the most common abnormal tachycardia in children
- Long QT syndrome and other inherited arrhythmias may first present in childhood or adolescence
- Congenital heart defects can be associated with specific arrhythmias
Inherited Arrhythmia Syndromes
Several genetic conditions can predispose individuals to dangerous arrhythmias:
- Long QT syndrome: Delayed repolarization of the heart, increasing risk of ventricular arrhythmias
- Brugada syndrome: Characterized by specific ECG abnormalities and increased risk of ventricular fibrillation
- Catecholaminergic polymorphic ventricular tachycardia (CPVT): Stress-induced ventricular arrhythmias
- Short QT syndrome: Accelerated repolarization, increasing risk of atrial and ventricular arrhythmias
- Arrhythmogenic right ventricular cardiomyopathy (ARVC): Progressive replacement of heart muscle with fatty tissue, leading to arrhythmias
When to Be Concerned
While many arrhythmias are benign, certain warning signs indicate the need for prompt medical attention:
- Arrhythmias that cause fainting or near-fainting
- Persistent or severe symptoms like chest pain, severe shortness of breath, or extreme fatigue
- Arrhythmias in people with known heart disease
- Family history of sudden cardiac death
- Arrhythmias that start suddenly and don’t stop on their own
- Very fast heart rates (over 150 beats per minute) at rest
Conclusion
Understanding the different types of arrhythmias can help you recognize potential issues and know when to seek medical care. While some arrhythmias are harmless, others require prompt treatment to prevent complications.