Continuation of systemic hormone therapy after myocardial infarction and risk of recurrent cardiovascular events: a SWEDEHEART nationwide cohort study

Background A clinical dilemma is how we should manage women currently on systemic hormone therapy at the time of a myocardial infarction (MI). Current guidelines generally discourage hormone therapy in women with established cardiovascular disease but provide limited guidance for those already receiving therapy at the time of MI. Contemporary evidence on the safety of continuation versus discontinuation of hormone therapy after MI is limited and inconclusive. Purpose To investigate whether continuation of systemic hormone therapy after MI is associated with increased risk of recurrent cardiovascular events or all-cause mortality within the first two years after discharge, and to evaluate whether cardiovascular risk profile influence this association. Methods This nationwide registry-based study included women aged 40–70 years with first MI recorded in the SWEDEHEART registry between 2006 and 2021. Hormone therapy exposure was obtained from the Swedish Prescribed Drug Register and based on dispensing patterns in relation to the index MI admission. Exposure was defined as at least one dispensed prescription of systemic hormone therapy within four months before admission. Continued use was defined as at least one dispensed prescription within four months after discharge, and women were categorised as discontinuers or continuers accordingly. The primary outcome was 1-year MACE, defined as recurrent MI, heart failure hospitalisation, unplanned coronary angiography or percutaneous coronary intervention (PCI), ischaemic stroke, arterial thrombosis, or all-cause death. To reduce misclassification and ensure accurate exposure classification, follow-up for outcomes began four months after discharge. Cox proportional hazards models were used to estimate hazard ratios (HR) with 95% confidence intervals (CI), adjusted for age, cardiovascular risk factors, and comorbidities. Kaplan–Meier survival curves were constructed and groups were compared using the log-rank test. Results Among 23 675 women (mean age 60.9 ± 7.3 years), 1818 (7.7%) were using hormone therapy prior to MI. Of these, 1139 (62.7%) continued therapy after MI, whereas 679 (37.3%) discontinued. During 1-year follow-up, 150 MACE events occurred, including 52 among discontinuers and 98 among continuers (crude HR 1.11, 95% CI 0.79–1.55, p=0.545). Continuation of hormone therapy was not significantly associated with increased risk of MACE compared with discontinuation (adjusted HR 1.11, 95% CI 0.79–1.56, p=0.540). At 2 years, there were a corresponding trend towards higher risk among continuers that did not reach statistical significance (log-rank p=0.084; adjusted HR 1.25, 95% CI 0.98–1.59, p=0.07). Conclusion Continuation of hormone therapy after MI was not associated with increased risk of recurrent cardiovascular events within the first year. However, a trend towards higher risk emerged beyond one year, suggesting that potential longer-term effects warrant further investigation.