Temporal context may shape the observed association between varenicline and outcomes after cardiac surgery

Yan et al. reported favorable postoperative cardiovascular outcomes associated with preoperative varenicline use in cardiac surgery patients. While their findings provide valuable real-world evidence, the 20-year study period raises the possibility of calendar-time confounding, as both varenicline prescribing patterns and cardiac surgical care evolved substantially during this interval. Incorporating calendar year into matching or conducting era-stratified sensitivity analyses could help clarify whether the observed associations are independent of secular improvements in perioperative and cardiovascular care.