Coronary Artery Disease
Comparison of Long-Term Mortality of Patients Aged ≤40 Versus >40 Years With Acute Myocardial Infarction

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Young patients with acute myocardial infarction (MI) have a more favorable prognosis than older patients with MI. However, there are limited data comparing the prognosis of young patients with MI with young population controls. Comparison with an age-matched background population could unmask residual mortality risk in young patients with MI that would otherwise not be apparent when merely comparing the mortality risk of young and older patients with MI. We studied 15,151 patients with AMI from 2000 to 2005, of which 601 patients were ≤40 years (young MI). The relative survival ratio (RSR) was calculated as the ratio of the observed survival of patients with MI divided by the expected survival, estimated from the background population (n = 3,771,700) matched for age, gender, and follow-up year. An RSR of <1.0 or >1.0 indicates poorer or better survival, respectively, than the background population. The 12-year all-cause and cardiovascular mortality of young versus older patients was 12.8% versus 50.7% (p <0.001) and 9.2% versus 34.5% (p <0.001), respectively. The adjusted hazard ratio (95% confidence interval) for all-cause and cardiovascular mortality comparing young with older patients was 0.20 (0.16 to 0.27) and 0.27 (0.20 to 0.36), respectively. The RSR (95% confidence interval) of young and older patients was, respectively, 0.969 (0.950 to 0.980) and 0.804 (0.797 to 0.811) at 1 year, 0.942 (0.918 to 0.960) and 0.716 (0.707 to 0.726) at 5 years, and 0.908 (0.878 to 0.938) and 0.638 (0.620 to 0.654) at 9 years. In conclusion, despite a fivefold lower long-term mortality than older patients with MI, young patients with MI remain at significantly greater risk of long-term mortality than an age-matched background population.

Section snippets

Methods

This study was conducted according to the Declaration of Helsinki and approved by the institutional review boards of all 6 publicly funded hospitals in Singapore. All patients consecutively hospitalized for MI at the 6 hospitals are captured in this unselected registry that includes 96.0% of patients with MI in Singapore. The public health care system in Singapore provides health care access to all Singapore citizens and permanent residents through 3 interdependent government-led financing

Results

From the study population of 15,151 patients hospitalized for MI, 601 (4.0%) were ≤40 years, whereas 14,550 were >40 years (Table 1). Female was the minority gender in both the ≤40 and >40 age group, although the proportion of women was significantly lower in the ≤40 group. Among the ≤40-year-old patients with MI, the ethnic composition was as follows: 53.7% Chinese, 25.0% Malays, and 21.3% Indian, whereas that in the >40 group was 67.2%, 19.6%, and 13.2% for Chinese, Malay, and Indian,

Discussion

In our study of young patients with MI, age 40 was taken as the cutoff so as to achieve a balanced sensitivity and specificity in selecting biologically young patients. Moreover, age 40 was also one of the most commonly used cutoff in the existing literatures,3, 4, 5, 6, 7, 17 thus applying this same cutoff would allow comparisons with existing data. Among our Asian cohort of patients hospitalized for MI from 2000 to 2005, patients ≤40 years were uncommon with a prevalence of 4.0%. This is

Acknowledgment

The authors would like to acknowledge the efforts of all the clinical research co-ordinators from the Singapore Cardiac Databank, Singapore. They would also like to acknowledge Sandra Lim (National Registry of Diseases office) for linking data from the Singapore Cardiac Databank with mortality outcomes from the Singapore Births and Deaths Registry.

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    Drs Chua and Chan are co-senior authors.

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