[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [General pathology](https://durgical.com/en/general-pathology/) › [Heart](https://durgical.com/en/general-pathology/areas/heart/) › Arrhythmias and sudden cardiac death

# 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.

Updated Nov 12, 2026

## Key points

- Most adult sudden cardiac deaths: coronary artery disease with ventricular fibrillation, often without an acute infarct at autopsy.
- Young athletes: hypertrophic cardiomyopathy, arrhythmogenic cardiomyopathy, anomalous coronary origin, myocarditis, commotio cordis.
- Channelopathies leave a structurally normal heart: long QT (KCNQ1, KCNH2, SCN5A), Brugada (SCN5A), catecholaminergic polymorphic VT (RYR2), short QT.
- Sick sinus syndrome and AV block often come from age-related fibrosis of the conduction system; also ischemia, sarcoid, Lyme, Chagas.
- Atrial fibrillation follows atrial dilation and fibrosis (mitral disease, hypertension, heart failure); stasis gives atrial appendage thrombi.

## 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](https://durgical.com/en/conditions/myocardial-infarction/) | Acute ischemia or scar from old infarcts | Ventricular fibrillation or tachycardia |
| [Hypertrophic cardiomyopathy](https://durgical.com/en/conditions/hypertrophic-cardiomyopathy/) | Myocyte disarray, fibrosis | Ventricular fibrillation in the young |
| [Arrhythmogenic cardiomyopathy](https://durgical.com/en/conditions/arrhythmogenic-right-ventricular-cardiomyopathy/) | Fibrofatty replacement of the right ventricle | Ventricular tachycardia with exercise |
| [Long QT syndrome](https://durgical.com/en/conditions/long-qt-syndrome-and-torsades-de-pointes/) | Potassium or sodium channel mutation; normal structure | Torsades de pointes |
| [Brugada syndrome](https://durgical.com/en/conditions/brugada-syndrome/) | Sodium channel (SCN5A) loss of function | Polymorphic VT, ventricular fibrillation at rest or sleep |
| [Wolff–Parkinson–White](https://durgical.com/en/conditions/wolff-parkinson-white-syndrome/) | Accessory AV pathway | Re-entrant tachycardia, fast AF |
| [Conduction system disease](https://durgical.com/en/conditions/atrioventricular-block/) | 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.

## Memory aid

Old heart, scar and fibrillation; young heart, think muscle (HCM, ARVC) or the wires' insulation (channelopathy).

## 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.

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## Elsewhere in DurgiPedia

- [The cardiac conduction system](https://durgical.com/en/physiology/the-cardiac-conduction-system/)
- [The heart wall, valves and conduction tissue](https://durgical.com/en/histology/the-heart-wall-valves-and-conduction-tissue/)

## Connections

## Related 5

- [Ischaemic heart disease](https://durgical.com/en/general-pathology/ischaemic-heart-disease/)
- [Hypertrophic cardiomyopathy](https://durgical.com/en/general-pathology/hypertrophic-cardiomyopathy/)
- [Arrhythmogenic cardiomyopathy](https://durgical.com/en/general-pathology/arrhythmogenic-cardiomyopathy/)
- [Chagas heart disease](https://durgical.com/en/general-pathology/chagas-heart-disease/)
- [The autopsy: clinical and medicolegal](https://durgical.com/en/general-pathology/the-autopsy-clinical-and-medicolegal/)

## Related conditions 10

- [Cardiac arrest (VF, pulseless VT, asystole, PEA)](https://durgical.com/en/conditions/cardiac-arrest/)
- [Long QT syndrome and torsades de pointes](https://durgical.com/en/conditions/long-qt-syndrome-and-torsades-de-pointes/)
- [Brugada syndrome](https://durgical.com/en/conditions/brugada-syndrome/)
- [Sinus node dysfunction (sick sinus syndrome) and symptomatic bradycardia](https://durgical.com/en/conditions/sinus-node-dysfunction-and-symptomatic-bradycardia/)
- [Atrioventricular (heart) block](https://durgical.com/en/conditions/atrioventricular-block/)
- [Atrial fibrillation](https://durgical.com/en/conditions/atrial-fibrillation/)
- [Wolff-Parkinson-White syndrome](https://durgical.com/en/conditions/wolff-parkinson-white-syndrome/)
- [Arrhythmogenic right ventricular cardiomyopathy](https://durgical.com/en/conditions/arrhythmogenic-right-ventricular-cardiomyopathy/)
- [Hypertrophic cardiomyopathy](https://durgical.com/en/conditions/hypertrophic-cardiomyopathy/)
- [Ventricular tachycardia](https://durgical.com/en/conditions/ventricular-tachycardia/)

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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](https://medlineplus.gov/arrhythmia.html) (MedlinePlus, US National Library of Medicine, 2025); [Ventricular fibrillation: MedlinePlus Medical Encyclopedia](https://medlineplus.gov/ency/article/007200.htm) (MedlinePlus, US National Library of Medicine, 2025); [Atrioventricular Block](https://www.ncbi.nlm.nih.gov/books/NBK459147/) (StatPearls (NCBI Bookshelf), 2025).

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License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/general-pathology/arrhythmias-and-sudden-cardiac-death/