Definition and epidemiology
Arrhythmia is a broad term encompassing any deviation from normal sinus rhythm, including abnormalities of impulse formation (automaticity, triggered activity) or impulse conduction (reentry, block). Arrhythmias are classified by rate (tachyarrhythmia vs bradyarrhythmia), origin (supraventricular vs ventricular), and mechanism.
- Atrial fibrillation (AF) is the most common sustained arrhythmia, affecting roughly 1-2% of the general population, with prevalence rising sharply after age 65 and approaching 10% in those over 80.
- Premature atrial and ventricular contractions are extremely common and often incidental findings on Holter monitoring in healthy individuals.
- Sudden cardiac death from ventricular arrhythmias accounts for a substantial proportion of cardiovascular mortality worldwide, most often in the setting of ischemic heart disease.
- Arrhythmias in structurally normal hearts (e.g., Wolff-Parkinson-White, long QT syndrome) are less common but disproportionately represented on exams due to distinctive ECG patterns.
- Irregularly irregular rhythm with no discrete P waves = atrial fibrillation
- Reentry is the most common mechanism underlying clinically significant arrhythmias
- Unstable arrhythmia (hypotension, chest pain, altered mental status) = immediate synchronized cardioversion
- CHA2DS2-VASc score guides anticoagulation decisions in atrial fibrillation
- Adenosine is first-line pharmacologic treatment for stable SVT after vagal maneuvers fail
- Torsades de pointes is associated with QT prolongation and treated with IV magnesium
- Wolff-Parkinson-White shows a short PR interval and delta wave on ECG
- ICD is indicated for secondary prevention after sustained VT/VF and select primary prevention in low EF
Etiology and risk factors
Causes can be structural, electrical, metabolic, or iatrogenic.
Structural and ischemic
- Coronary artery disease and prior myocardial infarction (scar-related reentry)
- Cardiomyopathies (dilated, hypertrophic, arrhythmogenic right ventricular)
- Valvular heart disease, especially mitral stenosis (predisposes to AF)
- Congenital heart disease and prior cardiac surgery
Electrical and genetic
- Accessory conduction pathways (Wolff-Parkinson-White)
- Channelopathies: long QT syndrome, Brugada syndrome, catecholaminergic polymorphic VT
- Sick sinus syndrome, AV nodal disease
Metabolic and systemic
- Electrolyte disturbances: hypokalemia, hyperkalemia, hypomagnesemia, hypocalcemia
- Thyrotoxicosis (common precipitant of AF)
- Hypoxia, acidosis, sepsis
Iatrogenic and toxic
- QT-prolonging drugs (certain antiarrhythmics, macrolides, antipsychotics, antiemetics)
- Digoxin toxicity
- Stimulants: caffeine, alcohol ("holiday heart"), cocaine, amphetamines
Other risk factors
- Age, hypertension, obesity, obstructive sleep apnea, diabetes, smoking, and family history of sudden cardiac death
Pathophysiology
Arrhythmias arise from three basic mechanisms:
- Abnormal automaticity: ectopic foci (atrial, junctional, or ventricular) fire spontaneously due to altered ion channel function, common in ischemia or electrolyte imbalance.
- Triggered activity: afterdepolarizations occurring during or after repolarization, implicated in digoxin toxicity and long QT-associated torsades de pointes.
- Reentry: the dominant mechanism in most clinically significant arrhythmias (AF, AVNRT, ventricular tachycardia post-MI). Requires an anatomical or functional circuit with two pathways of differing conduction velocity and refractoriness, allowing a wavefront to continuously circulate.
In atrial fibrillation, multiple wavelets of reentry and ectopic firing (often from pulmonary vein sleeves) cause chaotic atrial activation, loss of effective atrial contraction, and irregular ventricular response governed by AV node filtering. In ventricular tachyarrhythmias post-infarction, scar tissue creates slow conduction zones that support macroreentrant circuits.
Clinical features
Presentation ranges from asymptomatic to sudden cardiac death.
- Palpitations (fluttering, pounding, or skipped beats)
- Dizziness, presyncope, or syncope
- Dyspnea and fatigue, especially with rate-related reduction in cardiac output
- Chest discomfort, particularly if underlying ischemia
- Signs of hemodynamic compromise: hypotension, altered mental status, pulmonary edema in unstable tachyarrhythmia
- Irregular pulse (classic for AF) or bradycardia with signs of poor perfusion
- Many arrhythmias, especially paroxysmal AF or isolated PVCs, are entirely asymptomatic and detected incidentally
Diagnosis
Diagnosis relies on correlating symptoms with documented rhythm abnormality.
Initial evaluation
- 12-lead ECG is the cornerstone: assess rate, rhythm regularity, P wave morphology, QRS width, and QT interval
- Continuous telemetry or rhythm strip during symptomatic episodes
Ambulatory monitoring (for paroxysmal symptoms)
- Holter monitor (24-48 hours) for frequent symptoms
- Event recorder or implantable loop recorder for infrequent symptoms
Additional workup
- Electrolytes (potassium, magnesium, calcium), TSH, troponin if ischemia suspected
- Echocardiogram to assess structural heart disease, ejection fraction, valve function
- Electrophysiology study for mechanism characterization or pre-ablation mapping
- Exercise stress testing if arrhythmia is exertional or ischemia is suspected
Key ECG patterns
| Arrhythmia | Key ECG feature |
|---|---|
| Atrial fibrillation | Irregularly irregular, no discrete P waves |
| Atrial flutter | Sawtooth flutter waves, often 2:1 conduction |
| AVNRT | Regular narrow QRS, P waves hidden or retrograde |
| Ventricular tachycardia | Wide QRS, regular, AV dissociation |
| Torsades de pointes | Polymorphic VT with twisting QRS axis, prolonged QT |
| Complete heart block | AV dissociation, regular but independent P and QRS rates |
Differential diagnosis
- Panic disorder or anxiety (palpitations without documented arrhythmia)
- Vasovagal syncope (distinguish from arrhythmic syncope)
- Thyrotoxicosis (can mimic or cause sinus tachycardia and AF)
- Pheochromocytoma (episodic palpitations with hypertension)
- Electrolyte-induced ECG changes without true structural arrhythmia
- Artifact on telemetry or ECG lead misplacement mimicking arrhythmia
Management
Treatment depends on arrhythmia type, hemodynamic stability, and underlying cause. Unstable patients (hypotension, altered mental status, ischemic chest pain, pulmonary edema) require immediate synchronized cardioversion (or defibrillation for pulseless VT/VF) per ACLS protocols, regardless of specific rhythm diagnosis.
Atrial fibrillation
- Rate control (beta-blockers or non-dihydropyridine calcium channel blockers) is first-line for most patients
- Rhythm control (antiarrhythmics or catheter ablation) considered for symptomatic patients or those failing rate control; guideline emphasis on early rhythm control has increased in recent US and European recommendations for selected patients
- Anticoagulation guided by validated stroke risk scores (CHA2DS2-VASc); direct oral anticoagulants are preferred over warfarin in most eligible patients per current ACC/AHA and ESC guidance
Supraventricular tachycardia (AVNRT/AVRT)
- Vagal maneuvers first
- IV adenosine if vagal maneuvers fail
- Catheter ablation for recurrent or symptomatic cases
Ventricular tachycardia
- Stable monomorphic VT: antiarrhythmic (amiodarone or procainamide) or synchronized cardioversion
- Pulseless VT/VF: immediate defibrillation and ACLS algorithm
- Implantable cardioverter-defibrillator for secondary prevention after sustained VT/VF, and primary prevention in select high-risk structural heart disease
Bradyarrhythmia and heart block
- Address reversible causes (drugs, electrolytes, ischemia)
- Permanent pacemaker for symptomatic sinus node dysfunction or high-grade AV block
General principles
- Correct underlying electrolyte and metabolic abnormalities
- Discontinue or avoid QT-prolonging agents when torsades is a concern
- Risk stratify for sudden cardiac death in cardiomyopathy and channelopathy patients
Complications and prognosis
- Thromboembolism and stroke, particularly with atrial fibrillation and flutter
- Tachycardia-induced cardiomyopathy from prolonged uncontrolled rapid rhythms
- Hemodynamic collapse and cardiac arrest with sustained ventricular tachyarrhythmias
- Sudden cardiac death, especially in untreated channelopathies or post-MI ventricular arrhythmia
- Prognosis is generally favorable for isolated ectopy and well-controlled AF with appropriate anticoagulation and rate/rhythm management
- Prognosis is guarded in structural heart disease with reduced ejection fraction and recurrent ventricular arrhythmias, where ICD therapy significantly improves survival
ABCD for AF management: Anticoagulation, Better rate/rhythm control, Cardiovascular risk factor management, Detection and monitoring
Practice questions
1. A 72-year-old woman with hypertension presents with palpitations and fatigue for 2 days. Her pulse is irregular at 110/min and blood pressure is 128/80 mmHg. ECG shows an irregularly irregular rhythm with no discrete P waves. She has no chest pain or altered mental status. Which of the following is the most appropriate immediate management?
2. A 25-year-old man with no past medical history develops palpitations during a soccer game. ECG shows a regular narrow-complex tachycardia at 180/min with no clearly visible P waves. Vagal maneuvers are attempted without resolution. Which medication is most appropriate next?
3. A 68-year-old man with a history of myocardial infarction 3 years ago presents with syncope. ECG during the event shows a wide-complex, regular tachycardia at 190/min with evidence of AV dissociation. He is now hemodynamically stable with blood pressure 118/76 mmHg. What is the most likely diagnosis?
Frequently asked questions
What causes arrhythmia?
Arrhythmias are caused by abnormalities in cardiac impulse formation or conduction, most often due to structural heart disease like coronary artery disease, cardiomyopathy, or valvular disease. Other common causes include electrolyte imbalances (potassium, magnesium), thyroid dysfunction, genetic channelopathies, drug toxicity, and stimulants such as caffeine, alcohol, or illicit drugs. Reentry circuits formed by scarred or diseased cardiac tissue are the most frequent mechanism in sustained arrhythmias.
What are the first symptoms of arrhythmia?
The earliest symptoms are usually palpitations, described as a fluttering, pounding, or skipped heartbeat sensation. Some people notice mild dizziness, fatigue, or shortness of breath, especially with exertion. Many arrhythmias, particularly early or intermittent atrial fibrillation, cause no symptoms at all and are discovered incidentally during a routine exam or ECG.
How is arrhythmia diagnosed?
Arrhythmia is diagnosed primarily with a 12-lead ECG performed during symptoms, which shows the characteristic rhythm abnormality. If symptoms are intermittent, ambulatory monitoring such as a Holter monitor, event recorder, or implantable loop recorder is used to capture the rhythm over days to months. Additional tests like echocardiography, blood electrolytes, and thyroid function help identify underlying causes.
Is arrhythmia curable?
Some arrhythmias, like AVNRT or Wolff-Parkinson-White, can be effectively cured with catheter ablation, which eliminates the abnormal electrical pathway. Others, such as atrial fibrillation in the setting of progressive structural heart disease, are typically managed long-term rather than cured, focusing on rate or rhythm control and stroke prevention. Prognosis and curability depend heavily on the specific arrhythmia type and underlying heart condition.
Atrial fibrillation vs atrial flutter — what is the difference?
Atrial fibrillation shows a chaotic, irregularly irregular rhythm with no discernible P waves, caused by disorganized electrical activity throughout the atria. Atrial flutter shows a regular sawtooth pattern of flutter waves, usually from a single reentrant circuit in the right atrium, often with a predictable conduction ratio like 2:1. Both increase stroke risk and are managed with similar rate control and anticoagulation principles, though flutter often responds especially well to catheter ablation.
Key drugs
Related conditions and differentials
Sources and further reading
StatPearls (NCBI Bookshelf)MedlinePlusWHO ICD-10: I49
Educational content for medical students, prepared by the WhiteCoat Pro editorial team with AI assistance; every page is reviewed by a second AI model for factual errors. It is not medical advice and does not replace the product label, local guidelines or a clinician.