Myocardial infarction in a population-based cohort of patients with biopsy-confirmed giant cell arteritis in southern Sweden

Objectives To determine the incidence rate (IR) of myocardial infarction (MI), relative risk of MI, and impact of incident MI on mortality in individuals with biopsy-confirmed giant cell arteritis (GCA). Methods MIs in individuals diagnosed with GCA 1998-2016 in Skåne, Sweden were identified by searching the SWEDEHEART register, a record of all patients receiving care for MI in a coronary care unit (CCU). The regional diagnosis database, with subsequent case review, identified GCA patients receiving care for MI outside of a CCU. A cohort of 10 reference subjects for each GCA case, matched for age, sex and area of residence, was used to calculate the incidence rate ratio (IRR) of MI in GCA to that in the general population. Results The GCA cohort comprised 1134 individuals. During 7958 person-years of follow-up, 102 were diagnosed with incident MI, yielding an IR of 12.8 per 1000 person-years (95% CI 10.3 to 15.3). The IR was highest in the 30 days following GCA diagnosis and declined thereafter. The IRR of MI in GCA to that of the background population was 1.29 (95% CI 1.05 to 1.59). Mortality was higher in GCA patients who experienced incident MI than in those without MI (HR 2.8; 95% CI 2.2 to 3.6). Conclusions The highest incidence of MI occurs within the 30 days following diagnosis of GCA. Individuals with GCA have a moderately increased risk of MI compared with a reference population. Incident MI has a major impact on mortality in GCA.