1. Introduction
Coronary heart disease (CHD) is the most common cause of death worldwide, and led to nearly 7 million deaths in 2010 (Lozano et al., 2013). Sudden cardiac death (SCD) often occurs with little warning and leads to death within an hour (Engdahl et al., 2002). SCD is important because it may happen in CHD patients who were previously stable, or who were not even recognized to have the disease (Zipes, 2005). Because CHD constitutes the major cause of SCD and most SCD occurs outside the hospital setting, outof-hospital coronary death (OHCD) is regarded as an approximate surrogate of SCD (Forastiere et al., 2005; Goraya et al., 2003). As the largest developing country in the world, China has changed its disease spectrum in the last few decades, with cardiovascular diseases becoming the primary cause of death. SCD is estimated to emerge as an important public health burden in China, especially in developed areas such as Shanghai