Sudden cardiac death after myocardial infarction in patients with type 2 diabetes

Background

Type 2 diabetes mellitus is a well-established risk factor for atherosclerosis, but its contribution to sudden cardiac death (SCD) risk after myocardial infarction (MI) is not well defined.

Objective

The purpose of this study was to compare the incidence and time-dependent risk of SCD in diabetic patients versus nondiabetic patients during 5-year follow-up after acute MI.

Methods

A total of 3,276 patients were enrolled at the time of acute MI between 1996 and 2005. Mean age at entry was 60 ± 11 years, and the cohort was followed until 2009. At entry into the study, diabetes was present in 629 (19.2%) patients. The primary endpoint was SCD, and the secondary endpoints were non-SCD and all-cause mortality.

Results

Among diabetic patients, the incidence of SCD was higher (5.9%) than in nondiabetic patients (1.7%), with a hazard ratio (HR) of 3.8 (95% confidence interval [CI] 2.4–5.8; P <.001) and adjusted HR of 2.3 (95% CI 1.4–3.8; P <.01). In diabetic patients with left ventricular ejection fraction >35%, the incidence of SCD was nearly identical to that of nondiabetic patients with ventricular ejection fraction ≤35% (4.1% vs 4.9%; P = .48). An excess in the incidence of non-SCD began to appear among diabetic patients within the first 6 months of follow-up (P <.001) but not in the incidence of SCD (P = .09). The excess in SCD among diabetic patients began to appear more than 6 months after the index event.

Conclusion

Patients with type 2 diabetes are at higher risk for SCD after MI than are nondiabetic patients. The incidence of SCD in post-MI type 2 diabetic patients with left ventricular ejection fraction >35% is equal to that of nondiabetic patients with left ventricular ejection fraction <35%.

Introduction

Type 2 diabetes mellitus is a common disorder in developed areas of the world. It also is considered a prominent component of the currently emerging epidemic of chronic diseases in less developed areas of the world. Worldwide prevalence is estimated to reach nearly 220 million people by the year 2010.¹ In addition to its implications as a primary disorder, type 2 diabetes mellitus is a powerful risk factor for other chronic diseases, most notably cardiac and vascular disease. For example, the population subset of diabetic patients has a higher prevalence of coronary artery disease, and patients with type 2 diabetes without prior evidence of coronary artery disease are at increased risk for having cardiovascular events earlier than nondiabetic patients. Type 2 diabetic patients have an increased risk for cardiovascular mortality with or without evident coronary artery disease at the time of diagnosis.2, 3, 4 A number of studies have suggested that diabetes is a risk factor for sudden cardiac death (SCD) as well as for other mechanisms of cardiac mortality,⁵ but data regarding fatal and nonfatal cardiac event rates among diabetic subjects without prior myocardial infarction (MI) compared to nondiabetic subjects with prior MI are conflcting.6, 7, 8 In one study, the risk of future events in type 2 diabetic patients without MI was as high as in nondiabetic patients with prior MI.⁶ In another study, diabetic patients without MI were at lower risk for future events.⁷ Neither study provided data on measures of infarct size, history of heart failure, or SCD as a specific primary or secondary endpoint.

SCD in the post-MI patient is of special interest because of the magnitude of risk, the challenge of individual risk profiling, and the potential for prevention in high-risk individuals.⁹ The previous observational studies comparing diabetic and nondiabetic patients with respect to death and cardiovascular morbidity after MI10, 11, 12, 13 or with respect to heart failure¹⁴ did not address the question of SCD risk. Only one of the MI studies¹⁰ and one heart failure study¹⁴ provided secondary analyses comparing SCD risk in diabetic and nondiabetic patients. A population-based observational study identified diabetes as a predictor of MI, non-SCD, and SCD, but the latter was not analyzed for SCD after MI because only 10% of the SCD cases had a prior MI.¹⁵ To our knowledge, no studies have focused on diabetes as a specific risk marker of SCD after MI. Furthermore, the duration of follow-up in prior studies of cardiovascular events in diabetic patients has been relatively short, and the majority of studies assessing the risk of cardiovascular mortality among diabetic patients were performed in 1990s, before the more recent advances in treatment of acute and chronic MI that improved the prognosis of affected patients. Because of current emphasis on the importance of identifying better clinical associations and biomarkers for SCD risk prediction, this study was designed to compare the contemporary incidence and temporal patterns of SCD in diabetic and nondiabetic patients during long-term follow-up after MI.