Comorbidity and risk of venous thromboembolism after hospitalization for first-time myocardial infarction: A population-based cohort study

Background Myocardial infarction (MI) is a risk factor for venous thromboembolism (VTE). Although comorbidities affect MI prognosis, it is unclear whether they affect VTE risk after MI. Objectives We examined the impact of comorbidity on VTE risk after MI. Methods We used nationwide population-based registries to identify first-time hospitalizations for MI and subsequent occurrence of VTE in Denmark (1995-2013). We included a comparison cohort from the general population matched 5:1 with MI patients by sex, age, and comorbidities. We computed 30-day and 1- to 12-month cumulative risks, rates, and hazard ratios of VTE. We also assessed the interaction between MI and comorbidity, defined as excess VTE risk in patients with both MI and comorbidity, by computing interaction contrasts and attributable fractions relating to the interaction. Results Thirty-day and 1- to 12-month VTE risks were 0.6% and 0.5% in the MI cohort (n = 160 338) and 0.03% and 0.3% in the comparison cohort (n = 792 384). The 30-day hazard ratio for VTE in the MI cohort was 23 (95% confidence interval, 20-27), which decreased during 1-year follow-up. Thirty days after MI, interactions between MI and comorbidity accounted for 16% and 39% of VTE rates in MI patients with low-to-moderate and high comorbidity, respectively. The interactions were driven primarily by hemiplegia and cancer. Conclusions Thirty-day VTE risk was substantially increased after MI compared with the general population. Although the absolute VTE risk was low, comorbidity substantially increased this risk, especially hemiplegia and cancer. VTE prophylaxis might be indicated in such high-risk patients but warrants further investigation.