Impact of Age on Antiplatelet Monotherapy in the Chronic Maintenance Period After Percutaneous Coronary Intervention: A Post Hoc Analysis From the HOST-EXAM Extended Study

Backgrounds: The HOST-EXAM Extended study reported the benefit of clopidogrel monotherapy over aspirin monotherapy in secondary prevention after percutaneous coronary intervention (PCI). This age-specific subgroup analysis of the study aimed to assess the impact of age on antiplatelet monotherapy after PCI. Methods: We analysed data from the per-protocol population (4717 patients) with a median follow-up of 5.8 years. The old age group comprised 2033 patients (43.1%), defined as those 65 years of age or older. The primary end point was the composite of all-cause death, nonfatal myocardial infarction, stroke, readmission due to acute coronary syndrome (ACS), and Bleeding Academic Research Consortium (BARC) bleeding type 3 or greater. The secondary end points were thrombotic composite outcomes and any bleeding. Results: Age correlated with an elevated risk of adverse events, particularly from age 65. Clopidogrel monotherapy was associated with a reduction of the primary end point in both the old age group (19.4% vs 23.1%, hazard ratio [HR] 0.802, 95% confidence interval [CI] 0.664-0.968; P = 0.022) and the young age group (7.8% vs 11.7%, HR 0.646, 95% CI 0.506-0.825; P < 0.001), without significant interaction (interaction P = 0.167). These findings were consistent for the secondary composite thrombotic end point and any bleeding events (interaction P value of secondary thrombotic end point: 0.786; interaction P value of any bleeding end point: 0.565). Consistent results were observed in analyses with a 75-year age cutoff and in subgroup analyses by 10-year age intervals. Conclusions: In patients requiring antiplatelet monotherapy after PCI, occurrence of both ischemic and bleeding events dramatically increased from age 65. The beneficial impact of clopidogrel over aspirin monotherapy was consistent regardless of age. Clinical Trial Registration Information: ClinicalTrials.gov Identifier: NCT02044250.