Developments in Implantable Cardioverter Defibrillator Therapy

William Foster, Mark Sopher
European Cardiology, 2012;8(2):98–100
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Abstract

Since the first implantable cardioverter defibrillator (ICD) implant in 1980, advances in the design of the devices, leads, detection algorithms and programming have led to major advances in device implantation, arrhythmia detection, recording and termination. Shocks from ICDs can be life-saving but increase morbidity, particularly when they are unnecessary or inappropriate. Recent evidence-based advances in programming have allowed reliable arrhythmia termination, in many cases without the need for shocks. The development of the subcutaneous ICD has allowed implantation in patients for whom vascular access may be difficult or best avoided. Remote monitoring of ICD patients allows some follow-up visits to be done in the patient’s home and increases the diagnostic data available to the ICD centre.
Keywords
Implantable cardioverter defibrillator, device implantation, arrhythmia, detection, reliable arrhythmia termination, remote monitoring
Disclosure The authors have no conflicts of interest to declare.
Received: January 11, 2012 | Accepted February 18, 2012 | Citation European Cardiology, 2012;8(2):98–100
Correspondence: Mark Sopher, Royal Bournemouth Hospital, Castle Lane East, Bournemouth, BH7 7DW, UK. E: Mark.Sopher@rbch.nhs.uk

In 1966, following the death of his mentor Professor Harry Heller from ventricular tachycardia (VT), Michel Mirowski began to research a way to prevent future deaths from ventricular arrhythmia, working with Morton Mower and William Staewen in Sinai Hospital, Baltimore. The first human implant of an automated implanted cardioverter defibrillator (ICD) took place in 1980 amid much criticism and scepticism from the medical community. Since then, ICD implants have increased exponentially, with expanding indications for implantation and increased identification of patients fulfilling implant criteria. Early implants required formal thoracic or abdominal surgical implantation under general anaesthesia, and rapid hardware development allowed completely transvenous lead implantation with much less invasive surgery under local anaesthesia.

Trials Supporting Use

Multiple clinical trials have confirmed the benefits of ICD therapy in reducing mortality. Early trials focused on secondary prevention of arrhythmic death following aborted cardiac arrest, with impressive reductions in mortality.1 Later studies sought to identify patients at primary risk of arrhythmic death; the Multicenter Automatic Defibrillator Implantation Trial (MADIT-I) study2 evaluated patients who had prior myocardial infarction (MI), impaired left ventricular (LV) function, non-sustained VT on ambulatory monitoring and a positive VT stimulation study. There was a clear mortality reduction with ICD implantation in this group. More recently, MADIT-II has shown that post-MI patients with an ejection fraction below 30 % and conduction delay evident on their electrocardiogram (QRS duration greater than 120 ms) benefit from ICD implantation without the need for further electrophysiological study or ambulatory monitoring.3

For non-ischaemic dilated cardiomyopathy, several trials have shown inconclusive effects on all-cause mortality, although the trend has been towards reduced mortality with ICD implantation. The Sudden Cardiac Death in Heart Failure Trial (SCD-HeFT), however, evaluated both ischaemic and non-ischaemic cardiomyopathy patients, and analysed the data for each separately. The non-ischaemic group had a very similar mortality reduction (risk ratio 0.74) to that of the ischaemic group (risk ratio 0.78), and the data reached statistical significance.4 More recently, a meta-analysis of ICD trials in patients with non-ischaemic cardiomyopathy showed a reduction in mortality of 27 %,5 in line with the survival benefit of ICD therapy in other patient groups.

These trials show that ICD implantation is superior to medical therapy at reducing mortality. The benefits are also sustained, with a 34 % reduction in mortality with ICD therapy compared with optimal medical therapy shown at eight years in the MADIT-II study group.6

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