Activated Clotting Time Platforms Matter: Evidence Gaps and Real-World Variability in Anticoagulation Targets During Left Atrial Ablation.

Background Activated clotting time (ACT) is used to guide intraprocedural heparin anticoagulation during left atrial ablation, with guideline-recommended target values generally assumed to be device-independent.Objective To assess whether measured ACT values differ across measurement platforms and whether contemporary anticoagulation strategies vary accordingly in clinical practice.Methods We performed a PRISMA-registered systematic review of studies directly comparing ACT values across different measurement platforms during left atrial ablation. In parallel, we conducted an international physician survey assessing ACT platforms, heparin dosing strategies and targeted ACT ranges.Results The systematic review identified four electrophysiology-specific studies comparing ACT platforms. Across all studies, simultaneously measured ACT values differed substantially between platforms, with mean paired differences of 50-60 seconds, corresponding to a 15-25% discrepancy at ACT targets of 300-350 s. These inter-platform differences persisted despite high correlation between devices. The survey was completed by 164 electrophysiologists (82% Europe, 13% North America). The most commonly used platforms were Hemochron (42%), Medtronic ACT Plus (27%), and Abbott i-STAT (16%). Target ACT ranges and heparin dosing strategies varied by platform: higher ACT targets and higher weight-based heparin doses were most frequently reported with Hemochron, lower targets and doses were more common with i-STAT; Medtronic users showed an intermediate pattern. Nearly one-third of respondents reported modifying heparin dosing after switching ACT platforms.Conclusion Available cross-validation data demonstrate substantial differences between ACT platforms. Real-world heparin administration strategies and ACT targets vary markedly by platform. These findings challenge the assumption of universal ACT targets and highlight the need for platform-specific interpretation.