Non-Pharmacological Management

Implantable Cardioverter-Defibrillators

Patients who survive an MI with left ventricular dysfunction are at high risk from sudden cardiac death, which is usually due to ventricular tachyarrhythmias (ventricular tachycardia and ventricular fibrillation).¹ There is therefore a need for interventions that reduce this risk.

Implantable cardioverter-defibrillators (ICDs) have been shown to reduce mortality in patients at risk of sudden cardiac death, including patients with MI.^2,3

Evidence

Several randomised controlled trials have investigated the ability of ICDs to improve clinical outcomes in patients with left ventricular dysfunction following MI.^2-5 Among these trials, one of the most important is the Multicenter Automatic Defibrillator Implantation Trial II (MADIT-II).³ In MADIT-II, patients with a left ventricular ejection fraction (LVEF) of 30% or less within the previous 3 months, and who had had an MI at least 1 month before enrolment, were randomised to receive an ICD or conventional therapy. After a mean follow-up of 20 months (range 6 days to 53 months), ICD therapy was associated with a 31% reduction in the risk of death compared with conventional therapy.

Guidelines

Current guidelines issued by the European Society of Cardiology (ESC) recommend the use of ICD devices in patients with ST-segment elevation MI (STEMI) who have:⁶

• LVEF ≤40% and in New York Heart Association (NYHA) functional class II or III, or 
• LVEF ≤35% and in NYHA functional class I.

In all cases, implantation should be deferred until at least 40 days post-MI.⁶ This recommendation is based on the results of DINAMIT (Defibrillator in Acute Myocardial Infarction Trial),⁴ which found that earlier ICD implantation did not improve mortality.

In addition to the above, ICD therapy should generally be reserved for patients expected to live for at least 1 year.¹

Economic considerations

In addition to those issued by ESC,⁶ there are numerous other guidelines on the use of ICDs to prevent SCD following MI. A review of these guidelines has shown that providing ICD therapy for all eligible patients would have major consequences for healthcare budgets.⁷ In an economic analysis based on the results of the MADIT-II trial,^3,8 the incremental cost of ICD therapy was calculated to be $US235,000 per life-year saved over a 3.5-year time-horizon, well above currently accepted thresholds for cost effectiveness. Thus, there is a need to identify those patients most likely to benefit from ICD therapy.

In an analysis also based on the results of the MADIT-II trial,³ Goldenberg and colleagues found that ICD therapy was associated with a significant mortality benefit (compared with conventional therapy) among patients with low LVEF and 1 or more of the following risk factors:⁹

• NYHA functional class >II 
• Age >70 years 
• Blood urea nitrogen >26 mg/dl 
• QRS duration >120 msec
• Atrial fibrillation.

In contrast, there was no evidence of a mortality benefit of ICD therapy in patients with none of these risk factors, nor in patients with advanced renal disease.⁹ These results may allow more effective targeting of ICD therapy to those most likely to benefit, thereby improving the overall cost effectiveness of treatment.