Measuring activated clotting time (ACT) from the left atrium versus venous femoral sheath during cryo-balloon ablation - does the sampling site matter

Abstract Background The activated clotting time(ACT) is used routinely to monitor and titrate anticoagulation therapy with unfractionated heparin(UFH) during ablation procedures in the left atrium(LA). Inadequate anticoagulation during LA ablation procedure increases the risk of systemic emboli, while excessive UFH use is associated with bleeding. Technically, ACT can be sampled from the femoral venous sheath or from oxygenized blood after crossing to the LA. The influence of the sampling site on ACT values has not been investigated. Methods A prospective observational study comparing ACT results of patients undergoing cryo-balloon pulmonary vein isolation(PVI). All patients were treated with UFH intravenously at a standardized dose of 100U per kg. ACT levels were sampled sequentially from the LA after trans-septal crossing via the long femoral sheath, and then from the femoral venous sheath. All samples were tested immediately on the same point of care ACT machine. Two tailed t-test was used to assess the mean difference between the sampling sites. Results 62 patients undergoing cryo-PVI consented and recruited to the study. 42% were female and only 4 patients were on concomitant aspirin treatment. Mean CHADS-VASC was 3.1 and 4 patients had CHADS-VASC=0 and were started on anticoagulation only after the procedure. One patient had a technical issue with ACT from the femoral vein. Mean ACT was 364±84 seconds when sampling from the LA and 360±65 seconds with the femoral venous sample(p=0.36). Among subgroups, patients weighting less than 80 kg and those not on Beta blocker therapy had significantly lower ACT results from venous testing. Conclusion No significant impact of the sample site, venous or from the LA, on ACT results during LA ablation was observed. Either approach to ACT sampling is permissible, and interchanging between these sampling methods during LA ablation is feasible for managing anticoagulation during ablation.ACT measurements for all patients