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Impact of sampling site on Activated Clotting Time (ACT) during cryoballoon ablation: Left atrium vs femoral sheath

Year: 2026

Type: article

Abstract: 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.

Source: American Heart Journal Plus Cardiology Research and Practice

DOI: 10.1016/j.ahjo.2026.100995