Activated Clotting Time Measured by Hemochron Signature Elite in Adult Cardiac Surgery: Implications for Clinical Practice

Objectives: To assess concordance between Hemochron Response (ACTr) and the three-activator device Hemochron Signature Elite (ACTe) in adult cardiac surgery patients. To evaluate the correlation between ACTe and anti-Xa values. Design: Multicenter, prospective observational study. Setting: University hospitals. Participants: Thirty-five elective adult cardiac surgery patients. Interventions: Patients received 300 IU/kg of unfractionated heparin (UFH) before cardiopulmonary bypass (CPB), as recommended by guidelines. ACTe was the reference device, with ACTe target ≥ 450 seconds required to establish adequate anticoagulation during CPB. Otherwise, an additional 100 IU/kg UFH was administered, up to a maximum cumulative dose of 500 IU/kg. Blood samples for ACTe and ACTr and samples for anti-Xa activity were collected simultaneously at baseline and after each UFH administration. The analyses included Pearson correlation, linear regression, and the Bland-Altman test. Measurements and main results: Thirty-five patients were enrolled (71% male, median age 68 years). After 300 IU/kg UFH, 13 (37%) patients required a second heparin dose due to ACTe less than 450 seconds despite ACTr ≥ 450 seconds and 5 (14%) due to ACT less than 450 seconds with both devices. Following the second UFH administration, 10/18 (55%) patients still did not reach the target ACTe despite an ACTr ≥ 450 seconds, requiring a third UFH administration. ACTe and ACTr showed no correlation (r = 0.157, p = 0.369). Linear regression analysis demonstrated limited agreement (R2 = 0.025). Bland-Altman analysis indicated a mean bias of -20.7% (95% CI -75.28% to +35.5%), with ACTe underestimating ACTr. The predicted ACTe, corresponding to an ACTr threshold of 450 seconds, was 357 seconds. Anti-Xa levels always exceeded 4 IU/mL, confirming adequate anticoagulation in all cases and were positively correlated to ACTe (r = 0.587, p < 0.001). Predicted ACTe interval corresponding to anti-Xa levels of 4 IU/mL was 263 to 515 seconds. Conclusions: ACTe and ACTr showed no correlation. Switching devices without adjusting ACT thresholds leads to unnecessary UFH redosing, despite adequate anticoagulation as measured by anti-Xa levels.