Variability in ACT Response to Standard UFH Bolus During PCI: A Prospective Study on Determinants of Subtherapeutic...

Unfractionated heparin (UFH) remains the standard anticoagulant during percutaneous coronary intervention (PCI), with guidelines recommending a target activated clotting time (ACT) of ≥250 s. However, despite receiving a standardized bolus dose, many patients fail to achieve this target.

To evaluate the effectiveness of standard UFH bolus dose in achieving the target ACT and to identify patient-related factors associated with suboptimal anticoagulant response.

This single-center, prospective observational study included 171 patients undergoing PCI between October 2024 and April 2025. All patients received a 100 IU/kg intravenous UFH bolus immediately before PCI. ACT was measured 5 min after administration, and additional 50 IU/kg boluses were given as needed to achieve an ACT ≥ 250 s. The primary endpoint was the proportion of patients achieving this target after the initial bolus. The secondary endpoint was the identification of factors associated with suboptimal anticoagulation.

Among 171 patients (mean age 68 years; 26.3% women), the target ACT was achieved in 35.7% (n = 61), while 64.3% (n = 110) did not. Active smoking was independently associated with failure to reach the target ACT (adjusted OR, 6.06; 95% CI, 1.41 to 43.8; p = 0.032), although the confidence interval was wide. Despite similar weight-adjusted UFH dosing and timing to ACT measurement, smokers had significantly lower ACT values (p < 0.001) and required higher cumulative UFH dose during PCI (p = 0.043). Propensity-score matching confirmed this association (p = 0.004).

In this prospective cohort, nearly two-thirds of patients did not achieve the recommended ACT target after a standard 100 IU/kg UFH bolus during PCI. Active smoking was independently associated with failure to reach therapeutic ACT levels, although this association should be interpreted cautiously. These findings underscore the variability of UFH response and reinforce the importance of ACT monitoring.