Significant differences between "high range" and "low range" point of care activated clotting time (ACT) assays during atrial fibrillation cryoablation

Abstract Introduction Anticoagulation with unfractionated heparin (UFH) is recommended during atrial fibrillation ablation (AFAbl) to maintain an activated clotting time (ACT) greater than 300 seconds. However, significant variability in the UFH dose required has been observed, influenced by patient and procedural factors. Among these, we have noted differing responses to similar UFH doses depending on the point-of-care ACT test from the same manufacturer: high range (HR) vs. low range (LR). Purpose Our aim was to study the impact of using two different ACT assays (HR vs. LR) to monitor anticoagulation levels during AFAbl. Both tests are approved for typical UFH doses and the target ACT (>300 seconds) recommended in AFAbl procedures. Currently, no guidance exists on which test should be preferred. Evidence of a differential response could necessitate a different approach to UFH dosing, with potential risks of over- or under-anticoagulation depending on the test used. Methods Our anticoagulation protocol includes uninterrupted or minimally interrupted oral anticoagulant therapy in previously anticoagulated patients. We administer an initial UFH bolus of 50-100 IU/kg at the operator's discretion immediately after transseptal access. ACT is initially tested with LR assays for each patient prior to vascular access, followed by tests every 30 minutes after the UFH bolus, with additional boluses as needed to achieve the target ACT. We do not routinely reverse anticoagulation after the procedure, and therapeutic anticoagulation is resumed immediately with low molecular weight heparin or oral anticoagulants, depending on patient recovery from sedation. In this study, we added simultaneous ACT determinations with HR tests. We evaluated 30 unselected patients during AF cryoablation, comparing HR and LR ACT test results at baseline and at 30-minute intervals. We also compared the percentage of patients who achieved the target ACT > 300 seconds in the standard practice group (LR test) versus the HR group. Results We observed significant differences in ACT values both at baseline (129.7 in LR vs. 151.9 in HR, p<0.01) and at 30 (311 in LR vs. 249.1 in HR, p<0.002) and 60 minutes (343.7 in LR vs. 247.4 in HR, p<0.01) post-UFH administration. HR assays showed higher baseline values but had a smaller increase compared to LR assays. These differences were consistent at both the 30- and 60-minute intervals. In the LR group, 50% of patients reached an ACT of at least 300 seconds, compared to only 10% in the HR group. No significant thrombotic or bleeding complications were observed in any patient. Conclusion We found potentially clinically relevant differences in ACT testing (HR vs. LR) during AFAbl procedures. These findings suggest that UFH dosing may vary significantly depending on the test used, posing potential risks of over- or under-anticoagulation. Currently, there are no recommendations regarding which test to use.Comparison of LR vs HR ACT values.