Implanting ICDs in Patients after Myocardial Infarction

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Abstract

In the MADIT II1 and the Sudden Cardiac Death in Heart Failure trial study (SCD-HEFT),2 a marked reduced incidence of cardiac death was found in patients with coronary artery disease and left ventricular ejection fraction of less than 0.30 or 0.35 respectively after implantation of an internal automatic defibrillator (ICD). These studies show that most patients with an earlier myocardial infarction die of malignant ventricular arrhythmias. Patients with dilated cardiomyopathy were also included in The SCD-HEFT study. The mortality registers in the US support these data.
The main question raised is: should all patients with an earlier myocardial infarction and EF below 35% be treated with an ICD? The consequence of implanting defibrillators in so many patients will be that many patients will receive an ICD with no need for it. It is of greatest importance to obtain better clinical or laboratory tests to help us in our daily clinical practice when defining more precisely who will have the best chance of benefiting from an ICD. A recent study, the Defibrillation in Acute Myocardial Infarction Trial (DINAMIT), presented at the American College Meeting in march 2004 shed some important light on this treatment in patients after myocardial infarction and the consecutive first months.3

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The immediate and 30 days mortality after myocardial infarction has decreased markedly in some countries like Norway4 and even in France with its earlier low mortality, over the last 10-15 years. This is mainly due to proper treatment with thrombolytic agents and beta-blockers, and also early percutaneous coronary intervention (PCI).5 The late mortality is also improved by the use of statins, beta-blockers and angiotensin-converting enzyme (ACE) inhibitors and A (angiotensin) I blockade.

In the MERIT study6 including patients with cardiac insufficiency and mainly NYHA class II and III functional class, the overall mortality was rather low after additional use of a selective beta-blocker. This beneficial effect has also been shown after other beta-blockers.7

The implementation of these well-documented therapies into clinical medicine is still not uniform and there is reason to suspect that great differences in mortality exist between patients treated by different doctors or hospitals.8 The individual skills of the doctors seem to play a major role in the outcome of the patients with cardiac insufficiency.9 Close follow-up of those patients can also decrease the mortality.

Many patients die from ventricular fibrillation after myocardial infarction, even after best medical therapy, and some of them also with high EF (ejection fraction). The automatic defibrillators implanted on proper indications may almost eliminate the chance of death in ventricular fibrillation in some patient groups.

Before going to the point of implanting a defibrillator, it is generally agreed that the best conventional treatment should be applied to patients after myocardial infarction. This includes PCI and, eventually, by-pass surgery. No benefit of ICDs was found in a primary prevention study where patients with an earlier myocardial infarction, a left ventricular EF of less than 0.36 and an abnormal signal averaged electrocardiogram (ECG) undergoing bypass surgery, were randomised to a defibrillator or not.10 Should the risk of death only be determined on the basis of an EF lower than 0.30-0.35?

The EF increases in many patients after myocardial infarction. At what time after the acute episode should a low EF have impact on implantation of an ICD? In patients where a QT dispersion lower than 52ms is found, a preserved EF or an improvement of EF is often described.10/>/>/>/>/>/>/>/>/>/>

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References

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  2. G Bardy, I Marchlinski, M Packer, et al., ├óÔé¼┼øSudden Cardiac Death Heart Failure Trial├óÔé¼┼Ñ, (in press) see ACC04online.org.
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