Key result
Left atrial ACT sampling is non-inferior to femoral venous sampling, differing by ~6 seconds.
Why the study?
Activated clotting time monitors unfractionated heparin during left atrial ablation, where inadequate anticoagulation increases thromboembolic risk and excessive dosing increases bleeding. Whether sampling from the left atrium versus a femoral venous sheath influences ACT values during atrial fibrillation ablation was unknown.
Does sampling blood from the left atrium provide non-inferior Activated Clotting Time (ACT) measurements compared to sampling from the femoral venous sheath in patients undergoing cryoballoon pulmonary vein isolation?
Observational (n=62)
Does sampling blood from the left atrium provide non-inferior Activated Clotting Time (ACT) measurements compared to sampling from the femoral venous sheath in patients undergoing cryoballoon pulmonary vein isolation?
Mean Difference: 6.1
Absolute Event Rate: 365% vs 359%
p-value: p=0.002 for noninferiority
ACT sampling from the left atrium is non-inferior to femoral venous sampling during cryoballoon ablation, allowing clinicians to reliably use either site for intraprocedural anticoagulation monitoring.
Left atrial ACT sampling may be interchangeable with femoral sampling during cryoballoon ablation; leaves open confirmation in randomized trials before practice change.
Background Activated clotting time (ACT) is used to monitor unfractionated heparin (UFH) during left atrial (LA) ablation procedures. Inadequate anticoagulation increases thromboembolic risk, while excessive UFH may increase bleeding. ACT can be sampled from a femoral venous sheath (ACT FV ) or from oxygenated blood within the LA (ACT LA ). The influence of sampling site on ACT values during atrial fibrillation ablation is unknown. Methods In this prospective observational study, consecutive patients undergoing cryoballoon pulmonary vein isolation received intravenous UFH. ACT was sampled sequentially from the LA and from a femoral venous sheath. All samples were analyzed on the same point-of-care ACT machine. Non-inferiority of LA relative to femoral venous sampling was tested against a 30-s margin, with agreement assessed by Cohen's kappa at 300 s and Bland-Altman analysis. Results Sixty-two patients were recruited (42% female; CHA 2 DS 2 -VASc 3.1 ± 1.8); 61 had paired samples. Mean ACT LA was 365 ± 83 and ACT FV was 359 ± 65 s ( p = 0.455). The mean paired difference (ACT LA − ACT FV ) was +6.1 s (upper one-sided 97.5% confidence limit +22.4 s), below the 30-s non-inferiority margin ( p = 0.002). Bland-Altman limits of agreement were − 119 to +131 s, with significant proportional bias (β = 0.288, p = 0.017). Dichotomized at 300 s, Cohen's kappa was 0.586 (moderate concordance). Conclusions ACT sampling from the LA was non-inferior to femoral venous sampling within a 30-s margin, supporting the use of either sampling site during LA ablation. Despite notable variability between paired measurements, unexpected ACT values should prompt repeat testing rather than be attributed to the sampling site.
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Margolis et al. (2026) conducted an observational in Atrial fibrillation undergoing cryoballoon pulmonary vein isolation (n=62). Left atrial (LA) blood sampling for Activated Clotting Time (ACT) vs. Femoral venous sheath (FV) sampling for ACT was evaluated on Activated Clotting Time (ACT, in seconds) (MD +6.1 s, 95% CI upper one-sided 97.5% CL +22.4 s, p=0.002 for noninferiority). ACT sampling from the left atrium was non-inferior to femoral venous sampling within a 30-s margin during cryoballoon ablation (mean difference +6.1 s; p=0.002 for non-inferiority).
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