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: This study aimed to assess whether measured ACT values differ across measurement platforms and whether contemporary anticoagulation strategies vary accordingly in clinical practice. METHODS: We performed a 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 4 electrophysiology-specific studies comparing ACT platforms. Across all studies, simultaneously measured ACT values differed substantially among platforms, with mean paired differences of 50-60 seconds, corresponding to a 15%-25% discrepancy at ACT targets of 300-350 seconds. These interplatform differences persisted despite high correlation among devices. The survey was completed by 164 electrophysiologists (82% from Europe and 13% from North America). The most 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; and users of Medtronic showed an intermediate pattern. Nearly one-third of respondents reported modifying heparin dosing after switching ACT platforms. CONCLUSION: Available cross-validation data indicate substantial differences among 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.