Arrhythmias and sudden cardiac death
- Topic
Most sudden cardiac deaths are a fatal rhythm in a diseased heart, usually coronary disease; in the young, inherited muscle or channel diseases dominate.
What it is
Arrhythmias arise from abnormal impulse formation or conduction. Their substrates include ischemia and scars, atrial dilation (atrial fibrillation), fibrosis or inflammation of the conduction system (sarcoid, Lyme, Chagas, age-related sclerosis), accessory pathways and inherited ion-channel diseases (channelopathies). Sudden cardiac death, unexpected death from a cardiac cause within an hour of symptoms, is usually ventricular fibrillation; coronary artery disease is the cause in most adults, while hypertrophic cardiomyopathy, arrhythmogenic cardiomyopathy, myocarditis, anomalous coronaries and channelopathies dominate in the young.
Structure
- Autopsy in sudden death: severe coronary disease with healed scars is most common; acute thrombi in a minority.
- In channelopathies the heart looks normal; genetic testing at autopsy (molecular autopsy) may find the cause.
Substrates of dangerous arrhythmias
| Substrate | Pathology | Typical arrhythmia |
|---|---|---|
| Ischaemic heart disease | Acute ischemia or scar from old infarcts | Ventricular fibrillation or tachycardia |
| Hypertrophic cardiomyopathy | Myocyte disarray, fibrosis | Ventricular fibrillation in the young |
| Arrhythmogenic cardiomyopathy | Fibrofatty replacement of the right ventricle | Ventricular tachycardia with exercise |
| Long QT syndrome | Potassium or sodium channel mutation; normal structure | Torsades de pointes |
| Brugada syndrome | Sodium channel (SCN5A) loss of function | Polymorphic VT, ventricular fibrillation at rest or sleep |
| Wolff–Parkinson–White | Accessory AV pathway | Re-entrant tachycardia, fast AF |
| Conduction system disease | Fibrosis, inflammation, granulomas, parasites | Sinus node dysfunction, complete heart block |
Clinical notes
- Survivors of cardiac arrest and high-risk patients receive implantable defibrillators.
- First-degree relatives of young people with sudden death should be screened.
Test yourself
Think of the answer, then tap the question to see it.
What is the most common cause of sudden cardiac death in adults?
Coronary artery disease leading to ventricular fibrillation.
Which two inherited channelopathies cause sudden death with a normal-looking heart?
Long QT syndrome and Brugada syndrome (also catecholaminergic polymorphic VT and short QT).
Which infections can damage the cardiac conduction system?
Lyme disease, Chagas disease and diphtheria; sarcoidosis is a non-infectious granulomatous cause.
Elsewhere in DurgiPedia
Connections
Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: Arrhythmia | Irregular Heartbeat | MedlinePlus (MedlinePlus, US National Library of Medicine, 2025); Ventricular fibrillation: MedlinePlus Medical Encyclopedia (MedlinePlus, US National Library of Medicine, 2025); Atrioventricular Block (StatPearls (NCBI Bookshelf), 2025).
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Representative model, for educational purposes only.