Activated Clotting Time Requires Adaptation Across Altered Measurement Devices: Determination of Appropriate Range During Atrial Fibrillation Ablation

Background: Methods for measuring activated clotting time (ACT) are not yet standardized. Objectives: To adjust and compare values between two measurement systems and to optimize ACT during atrial fibrillation (AF) ablation. Methods: Two systems were compared: electromagnetic detection using a rotating tube (EM system; Hemochron Response) and photo-optical detection using a cartridge immersed in blood (PO system; ACT CA-300TM). Results: ACT was measured simultaneously in 124 instances in 53 patients before and during AF ablations using both methods. A linear regression analysis showed ACT (EM system) = 1.19 x ACT (PO system) + 9.03 (p < .001, r = 0.90). Bland-Altman plots indicated an average difference of 50 s between the two systems. In 3364 ACT measurements from 1161 ablations, the EM system recorded a mean ACT of 320 +/- 44 s (range 156-487 s). Estimating the target range as mean +/- 1 SD range, the EM system's range was 275-365 s, in 5-s increments. The pre-ablation ACT measured on the EM system was 143 +/- 28 s (115-170 s). Cardiac tamponade occurred in 4 out of 2085 ablations (0.19%) over 5 years, with ACT values ranging from 330 to 391 s on the EM system. Based on these findings, the estimated optimal ACT range for the PO system was adjusted to 225-300 s to align with the EM system's range of 275-365 s. Conclusions: ACT target ranges should be system-specific, and direct extrapolation between devices is not recommended. Adjustment is clinically necessary when switching systems.