Prediction and prevention of sudden cardiac arrest.

1692 CMAJ, October 18, 2011, 183(15) © 2011 Canadian Medical Association or its licensors Major advances have been made in understanding the causes of and treatments for cardiovascular disease, and mortality related to such disease has been reduced. However, the incidence of sudden cardiac arrest has remained almost un changed for decades, generally affecting younger people (mean age about 65 yr) more so than other cardiovascular conditions causing death. Sudden cardiac arrest therefore represents a heavy burden to families, com munities and the health care system. Several reasons have been identified for the lack of improvement in outcomes for people at risk of premature, unexpected, sudden cardiac arrest, such as insufficient understanding of the mechanisms responsible or of the role played by genetic or environmental factors and the lack of good parameters for stratifying risk. The study by Reinier and colleagues published in the CMAJ has tested the hypothesis that environmental factors, such as those found in North American neighbourhoods with lower socioeconomic status, are associated with a higher incidence of sudden cardiac arrest. The high incidence of cardiac arrest is recognized as the predominant mechanism of sudden cardiac death, especially among patients with cor onary artery disease. As such, medical scientists and clinicians have sought ways of predicting and preventing these events. Previously identified variables that help predict the risk of sudden cardiac arrest among patients with structural heart disease include the left ventricular ejection fraction, various markers of cardiovascular autonomic function, electrical markers measured from standard and exercise electrocardiograms and biomarkers such as plasma levels of natriuretic peptides and markers of inflammation. Despite the multiplicity of factors known to be related to an increased risk of sudden cardiac death, the only clinical practice currently used to predict such an event is the measurement of left ventricular ejection fraction. Use of this measurement for stratifying risk is based on the re sults of randomized trials of implantable defibrillators, which have shown a mortality benefit for patients with depressed left ventricular ejection fraction (< 35%), especially after a myocardial infarction (> 40 d after event). Although left ventricular ejection fraction stratifies risk of sudden cardiac arrest for a specific subgroup of patients, it is an inadequate predictor of overall incidence because most randomized trials have focused on patients at high risk (i.e., patients who account for a low cumulative number of events). Therefore, the results of these studies cannot be accurately applied to the general population and have probably not had a substantial effect on the overall incidence of sudden cardiac arrest, as seen in statistics from the United States, despite the widespread use of such devices. Traditional coronary risk factors, such as high cholesterol and hypertension, do not specifically identify those patients at high risk for sudden cardiac arrest. Studies involving samples drawn from the general population have shown that certain clinical and demographic variables are associated with risk of sudden cardiac arrest, such as male sex, exercise capacity, vital capacity, heart rate, having diabetes, obesity and smoking. Some electrocardiographic features, such as an early repolarization pattern in the inferior leads of a standard 12-lead electrocardiogram, have also recently been shown to predict the occurrence of sudden cardiac death in the general population. Factors such as obesity, diabetes, exercise habits and smoking could be mitigated using widespread population-based preventive stratePrediction and prevention of sudden cardiac arrest