Sudden Death After Myocardial Infarction

Abstract & Commentary

By John P. DiMarco, MD, PhD, Professor of Medicine, Division of Cardiology, University of Virginia, Charlottesville. Dr. DiMarco is a consultant for Novartis, and does research for Medtronic and Guidant.

Source: Adabag AS, et al. Sudden death after myocardial infarction. JAMA. 2008;300:2022-2029.

In this paper, Adabag et al from the Mayo Clinic analyzed the risk of sudden death after an acute myocardial infarction over a 28-year period in patients residing in Olmsted County, MN. Virtually all medical care in this area is provided by a small number of providers who share their patient database, allowing accurate, long-term epidemiological studies. Patients who survived to hospital discharge after a diagnosis of acute myocardial infarction were identified. Baseline demographic and clinical characteristics were collected and long-term outcomes determined. Sudden cardiac death was defined as any out-of-hospital death for which the primary cause of death was classified as coronary heart disease by the death certificate.

Between 1979 and 2005, a total of 3,296 incident myocardial infarctions occurred in Olmsted County. There were 2,997 hospital survivors. The mean age for survivors was 67; 59% were male. Most events were non-ST segment elevation myocardial infarctions (66%). Reperfusion and/or revascularization were performed in 52% of the group. Over a median follow-up of 4.7 years, 1,160 deaths occurred among the hospital survivors. Of these deaths, 282 (24%) were classified as sudden cardiac deaths. Thirty-five of these sudden cardiac deaths occurred during the first 30 days following hospital discharge. After that, the rate of sudden cardiac death was constant at 1.2% per year. Patients who experienced sudden cardiac death were older, more likely to be women, and to have a history of hypertension, diabetes, and other comorbidities. They were also more likely to have more signs of heart failure, have had an anterior myocardial infarction, and were less likely to have been treated with reperfusion or revascularization. The risk of sudden death after myocardial infarction decreased over time. Compared with the sudden death rate during the first nine years of the study, the risk was 20% lower in the middle nine years and 38% lower in the last nine years. Recurrent ischemia and heart failure were common after myocardial infarction, with 69% of the group having one or both. Recurrent ischemia was not associated with the risk for sudden death after adjustment for other clinical variables. However, heart failure showed a strong adverse association with sudden cardiac death, even after adjustment for these variables with a hazard ratio of 4.2. There were only 50 patients who received an implantable cardioverter defibrillator (ICD) in this sample, so ICD therapy had little effect on the reported sudden death rates.

Adabag et al conclude that the risk for sudden cardiac death is highest during the first month after myocardial infarction and then continues at a much lower frequency during long-term follow-up. Heart failure is the strongest predictor of sudden cardiac death after MI. The risk for sudden death has decreased significantly over time.

Commentary

This report is an interesting look at the changing epidemiology of sudden death after myocardial infarction. Adabag et al looked at all patients who were coded as having a myocardial infarction, not just those in whom it was the principal diagnosis. The definition of sudden death as an out-of-hospital death caused by coronary heart disease is also somewhat different from the more common definition. However, the trends identified are probably valid and provide insights into the problem. Clearly, the risk for sudden death has decreased over time as therapies for ischemia, heart failure, and risk factor reduction have improved. After the first 30 days after discharge, the sudden death rate was only 1.2% per year. Heart failure, however, increased the risk more than four-fold.

The very early period after discharge was associated with the highest risk of sudden death, and preventing sudden death in this period remains a clinical problem. In the DINAMIT study, ICD therapy in high-risk patients identified in this time frame did not improve overall survival. Although arrhythmic mortality was decreased in the ICD group, there were more heart failure deaths, and the result was no benefit. It seems likely that the key to preventing sudden death in this early period will be improvements in managing the acute infarction and its early complications.