Despite major advances during the past two decades in the management of patients with acute myocardial infarction, sudden cardiac death remains an important contributor to overall mortality, according to Reginald Liew, National Heart Centre, Singapore, in a recent review in the British Medical Journal, “Implantable cardioverter defibrillators after acute myocardial infarction”.
Liew looked at various studies to support the argument that there is no evidence to suggest survival benefit if implantable cardioverter defibrillators are inserted within 40 days after an acute myocardial infarction.
A 2008 study by Fox et al examining temporal trends in sudden cardiac death and non-sudden coronary heart disease from 1950 to 1999 found the risks of sudden coronary heart disease and non-sudden coronary heart disease mortality had decreased by 49% to 64% over the past 50 years. “These trends were evident in subjects with and without heart disease, which suggests important contributions of primary and secondary prevention to the decreasing risk of coronary heart disease death and coronary heart disease”, they concluded.
The risk of sudden death is highest in the first 30 days after myocardial infarction among patients with left ventricular dysfunction and/or heart failure. An earlier implementation of strategies for preventing sudden death may be warranted in selected patients, found a study by Solomon et al which assessed the incidence and timing of sudden unexpected death or cardiac arrest with resuscitation in 14,609 patients with left ventricular dysfunction and/or heart failure after myocardial infarction.
Two trials found the insertion of an implantable cardioverter defibrillator at an early stage did not reduce all cause mortality, despite the risk of sudden cardiac death being the greatest in the first 30 days after acute myocardial infarction.
In DINAMIT (Defibrillator in acute myocardial infarction trial) 674 patients were randomised to either implantable cardioverter defibrillators therapy or no implantable cardioverter defibrillators therapy six to 40 days after a myocardial infarction.
Investigators concluded that prophylactic implantable cardioverter defibrillators therapy did not reduce overall mortality in high-risk patients who recently had a myocardial infarction. Implantable cardioverter defibrillator therapy was associated with a reduction in the rate of death due to arrhythmia, offset by an increase in the rate of death from nonarrhythmic causes.
The IRIS (Immediate risk stratification improves survival) trial found that the risk of sudden cardiac death was reduced by implantable cardioverter defibrillator therapy but was offset by an increase in the risk of non-sudden cardiac death, a finding which requires further study.
Liew refers to a recent study by Pouleur et al which assessed autopsyrecords in a 398 cases (14% of deaths) classified as sudden death events in patients from the VALIANT (Valsartan in acute myocardial infarction) trial as shedding light on why early insertion of an implantable cardioverter shortly after acute myocardial infarction may not improve survival.
They found that recurrent myocardial infarction or cardiac rupture accounted for a high proportion of sudden death in the early period after acute myocardial infarction, with arrhythmic death a subsequent likely cause.
The findings further support the notion that non-arrhythmic death may be a more important cause of death in the early stages after acute myocardial infarction, explaining the overall lack of benefit on mortality when implantable cardioverter defibrillators are inserted within one month, added Liew.
In his own 2010 paper published in the Annals Academy of Medicine, Liew asks “When is the optimal time to insert an implantable cardioverter defibrillator?” before adding, “The answer is still unresolved, although current evidence suggests no overall survival benefit for devices inserted within 40 days of infarction. Clearly, more work is needed in this area to refine the optimal clinical and cost-effective approach.”