Background: Sleep impairment such as insomnia is an established risk factor for the development of cardiovascular disease and acute myocardial infarction (AMI). The aim of the current study was to examine the association between insomnia and all-cause mortality among AMI patients.
Methods: This prospective cohort study used data on n=732 patients recruited from September 2006 to May 2011 as part of the Västmanland Myocardial Infarction Study (VaMIS), a prospective cohort study of AMI patients living in Västmanland County, Sweden. Participants were followed up for all-cause mortality until December 9, 2015. The outcome of interest was time-to-death (TTD), with the presence of insomnia being the risk factor of main interest. Data were analyzed using a piecewise Cox regression model with change point for insomnia at two years of follow-up, adjusted for socioeconomic, lifestyle and clinical risk factors.
Results: In total, n=175 (23.9%) of the participants suffered from insomnia. During a mean (SD) follow-up time of 6.0 (2.5) years (4392person-years), a total of n=231 (31.6%) participants died, n=77 (44.0%) in the insomnia group and n=154 (27.6%) in the non-insomnia group (log-rank test p<0.001). In a multiple adjusted piecewise Cox regression model, insomnia did not imply a higher risk of death during the first two years after AMI (HR 0.849; 95% CI 0.508-1.421; p=0.534). During the period after the first two years, however, insomnia implied a 1.6 times higher risk of death (HR 1.597; 95% CI 1.090-2.341; p=0.016).
Conclusions: Insomnia implies a higher risk of death among AMI patients in the long term.
Keywords: Acute myocardial infarction; All-cause mortality; Cardiovascular epidemiology; Insomnia; Long-term follow-up; Survival analysis.
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