Myocardial Infarction

• Introduction

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• ST Elevation Infarction
• Thrombolytic Therapy- Reducing Mortality
• Thrombolytic Therapy- Additional Benefits

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• Assessing Extent of Infarction
• ECG and Q Waves

Myocardial Infarction- Reducing Sudden Cardiac Death

With Prophylactic Implantable Defibrillator Therapy

Patients with ischaemic heart disease are at risk of sudden death. Those with significant impairment of left ventricular systolic function are at higher risk.

If beta-blockers are regarded as anti-arrhythmic drugs, then only this anti-arrhythmic class has been shown to reduce risk of sudden death after myocardial infarction. Flecainide, encainide and morizicine have been shown to increase risk of death in patients when used in post-myocardial infarction patients with ventricular ectopy. An isomer of sotalol (d-sotalol) was also shown to increase mortality when used prophylactically after myocardial infarction. Amiodarone has been shown to have a neutral effect on overall mortality after myocardial infarction.

Non-randomised data had shown that implantable defibrillators (ICD) not only reduced risk of sudden death but reduced overall mortality. In other words, patients that were "saved" from sudden death did not all necessarily go onto die within a short period of other cardiac causes such as progressive heart failure.

The MADIT I trial (N Engl J Med 1996;335:1933-40) enrolled patients with ischaemic heart disease with an ejection fraction less than thirty percent and who had had an episode of non-sustained ventricular tachycardia. Patients were randomised to usual therapy or implantation of an ICD. After an average follow-up of 27 months, mortality was reduced by 54 percent. Interestingly, in this study patients with ICD has lower arrhythmic and lower non-arrhythmic mortality rates.

The MADIT II (N Engl J Med 2002;346:887-883) study went one step further, there was no requirement for the patient to have had non-sustained ventricular tachycardia. Patients with ischaemic heart disease and an ejection fraction less than thirty percent were eligible for the study. After an average followup of 20 months, the mortality rate was reduced by 31 percent. The conventional therapy group has a mortality rate of 19.8 percent compared with the implantable defibrillator group mortality rate of 14.2%.

The findings of the study have major cost implications. In the United States of America, the "Medicare" system agreed to reimburse "MADIT type" patients provided they had a QRS duration greater than 120ms or had inducible ventricular tachycardia. This was a controversial decision but reduced the number of patients eligible for this therapy and thereby reducing the cost of providing this therapy.

The SCD-HeFT trial results were presented at the American College of Cardiology's Annual Scientific meeting this year (2004). This large trial enrolled patients with ischaemic and non-ischaemic cardiomyopathy. Eligible patients had an ejection fraction less than 35 percent and were in NYHA Class II or III symptoms. This trial showed reduction in five year all cause mortality by 23 percent.

In SCD-HeFT those assigned medical therapy were also randomised to amiodarone or placebo therapy. This trial found no benefit from prophylactic amiodarone therapy. There was a very high rate of use of ace-inhibitor and beta-blocker therapy.

Not all relevant studies are quoted in this brief article.

In New Zealand, so far, defibrillators are not routinely implanted prophylactically in this group of patients.