A cardioverter is a device that delivers a controlled electrical shock to the heart to restore a normal heart rhythm. The term is closely related to defibrillator, but cardioversion specifically refers to a synchronised shock (timed to coincide with the heart’s own electrical cycle) used to treat arrhythmias such as atrial fibrillation or ventricular tachycardia, whereas defibrillation uses an unsynchronised shock to treat the chaotic rhythm of ventricular fibrillation.
Cardioversion can be electrical (delivered by a device externally on the chest, or internally via an ICD) or chemical (using antiarrhythmic medication such as amiodarone or flecainide). External electrical cardioversion is performed under sedation or general anaesthetic in a hospital setting and is used for persistent atrial fibrillation or atrial flutter that has not reverted spontaneously or with medication.
Implantable cardioverter defibrillators (ICDs) combine both capabilities: they can deliver synchronised shocks for VT and defibrillation for VF, as well as providing pacing functions. For patients who experience frequent VT episodes, anti-tachycardia pacing (ATP) can often terminate VT painlessly before a shock is needed, reducing the burden of ICD shocks on quality of life.
For cardiac arrest survivors, understanding the difference between cardioversion (used in follow-up management of arrhythmias) and the shock their ICD is designed to deliver helps demystify device function and what to expect if their device activates.
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