Arrhythmia mechanisms - re-entry vs triggered activity vs automaticity
Core concept
- Re-entry - a circuit with unidirectional block + slow conduction lets the impulse re-excite recovered tissue -> the most common mechanism of clinically significant tachyarrhythmias (AVNRT, AVRT, atrial flutter, most VT)
- Automaticity - abnormal/enhanced spontaneous phase 4 depolarisation from a focus - sinus tachycardia, some atrial tachycardia, accelerated idioventricular rhythm
- Triggered activity - afterdepolarisations riding on or after the action potential
- Early afterdepolarisation (EAD) - during phase 2/3, from prolonged AP duration -> torsades de pointes (long QT)
- Delayed afterdepolarisation (DAD) - after full repolarisation, from Ca2+ overload -> digoxin toxicity arrhythmias, CPVT
3 more sections, plus exam facts
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