Implantable cardiac defibrillators: functions, construction and prevention roles
THE CONTEXT
Implantable cardiac defibrillators (ICDs) provide permanent pacemaker functions and can detect and terminate life-threatening ventricular tachyarrhythmias.
Device functions and construction
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ICDs terminate ventricular tachyarrhythmias using overdrive pacing, cardioversion or defibrillation.
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They are larger than pacemakers mainly because a large battery and capacitor are needed for cardioversion or defibrillation.
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ICD leads are usually slightly broader than pacing leads because they contain one or two shock coils for delivering defibrillation, in addition to their usual pacing functions.
Implantation and patient effects
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ICDs are implanted in a similar manner to pacemakers and carry a similar risk of complications.
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Patients may develop psychological problems and anxiety, particularly after repeated device shocks.
Primary and secondary prevention
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Secondary prevention applies after a potentially life-threatening ventricular arrhythmia has already occurred.
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Primary prevention applies when there is significant future risk of arrhythmic death.
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Primary prevention settings include ischaemic cardiomyopathy and inherited conditions associated with a high risk of sudden cardiac death, including long QT syndrome, hypertrophic cardiomyopathy and arrhythmogenic right ventricular cardiomyopathy.
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ICDs are expensive, so the indications routinely treated depend on available health-care resources.