Asthma Status and Risk of Incident Myocardial Infarction: A Population-Based Case-Control Study

Background The role of asthma status and characteristics of asthma in the risk of myocardial infarction (MI) are poorly understood. Objective We determined whether asthma and its characteristics are associated with risk of MI. Methods The study was designed as a population-based retrospective case-control study, which included all eligible incident MI cases between November 1, 2002, and May 31, 2006, and their matched controls. Asthma was ascertained using predetermined criteria. Active (current) asthma was defined as the occurrence of asthma-related episodes (asthma symptoms, use of asthma medications, unscheduled medical or emergency department visit, or hospitalization for asthma) within 1 year before MI index date. Results There were 543 eligible incident MI cases during the study period. Of the 543 MI cases, 81 (15%) had a history of asthma before index date of MI, whereas 52 of 543 controls (10%) had such a history (adjusted odds ratio [OR]: 1.68; 95% CI: 1.06-2.66) adjusting for risk factors for MI and comorbid conditions (excluding chronic obstructive lung disease). Although inactive asthma did not increase the risk of MI, individuals with active asthma had a higher odds of MI, compared with those without asthma (adjusted OR: 3.18; 95% CI: 1.57-6.44) without controlling for chronic obstructive pulmonary disease (COPD). After adjusting for COPD, although asthma overall was no longer statistically significant (adjusted OR: 1.34, 95% CI: 0.84-2.15), active asthma still was associated (adjusted OR: 2.33, 95% CI: 1.12-4.82). Conclusion Active asthma is an unrecognized risk factor for MI. Further studies are needed to assess the role of asthma control and medications in the risk of MI.