Atrial fibrillation and risk of myocardial infarction by sex and time since diagnosis. The Tromsø Study 1994–2021

AIMS: The relationship between atrial fibrillation (AF) and myocardial infarction (MI) remain unclear. We aimed to examine the sex-specific risk of MI, ST-segment elevation MI (STEMI) and non-ST-segment elevation MI (NSTEMI) in participants with AF, overall and by time since AF diagnosis. METHODS AND RESULTS: We followed 25 132 participants (53% women) from the Tromsø Study (1994-95) without AF and MI at baseline through 2021. Cox proportional- and Fine-Gray sub-distribution-hazard regression assessed AF as a risk factor for MI, STEMI and NSTEMI overall and by time since AF diagnosis (0 to <0.5, 0.5 to <1, 1 to <5, 5 to <10 and ≥10 years). During follow-up, 115 women and 124 men experienced incident AF and subsequent MI. AF was associated with increased hazard of MI in women (sub-distribution hazard ratio [sHR] 1.39, 95% confidence interval [CI] 1.12-1.72), but not in men. In women, the hazard of MI increased 1-10 + years since AF, peaking at ≥10 years (sHR 1.75, 95% CI 1.07-2.84). In men, hazard was increased within the first six months (sHR 2.27, 95% CI 1.45-3.54) but not thereafter. STEMI hazard was increased only in men within six months. NSTEMI hazard was elevated in women 1-10 + years since AF and in men within the first year. CONCLUSION: AF is a risk factor for MI in both sexes, but risk patterns differ. Women are at increased hazard of NSTEMI 1-10 + years since AF, while men are at increased hazard of STEMI within six months and NSTEMI within the first year.