A post hoc subgroup analysis？

After coronary stent placement, continuation of single antiplatelet therapy with aspirin is recommended in the AHA/ACC guidelines,whereas European guidelines favor individualized decisions based on bleeding and thrombotic risks.A post hoc subgroup analysis from the Perioperative Ischemic Evaluation-2 study among 470 patients undergoing noncardiac surgery with a prior coronary stent suggests perioperative aspirin use is associated with a reduction in 30-day death or nonfatal myocardial infarction (6.0% vs 11.5% without aspirin use; hazard ratio, 0.50 [95 CI, 0.26-0.95]).Other factors associated with perioperative risks after coronary stent placement include longer lengths of the treated coronary lesion and a history of acute coronary syndrome as the initial indication for stent placement (Figure 2).

在冠状动脉支架置放后，AHA/ACC指南建议继续单独使用阿司匹林进行抗血小板治疗，而欧洲指南则支持基于出血和血栓风险的个体化决策。对470名接受过非心脏手术并有冠状动脉支架的患者进行的围手术期缺血性评估-2研究的后亚组分析表明，围手术期服用阿司匹林与30天死亡或非致死性心肌梗死的减少相关（不使用阿司匹林的患者为6.0% vs使用阿司匹林的患者为11.5%；危险比，0.50 [95 CI，0.26-0.95]）。与冠状动脉支架放置术后围术期风险相关的其他因素包括需治疗的冠脉疾病的病史较长和因急性冠状动脉综合征作为支架放置的初始指征（图2）。

A post hoc subgroup analysis？如何理解？谢谢