Discrepancy between parallel anti-Xa and APTT is related to mortality in patients with Impella™ supported cardiogenic shock.

Background: Managing unfractionated heparin (UFH) during percutaneous mechanical circulatory support (PMCS) for cardiogenic shock (CS) is challenging due potential discrepancies between coagulation tests.

Objectives: To study the causes and consequences of discrepancies between anti-Xa and activated partial thromboplastin time (APTT) for UFH-monitoring during micro-axial flow pump support (Impella™) for CS.

Patients/methods: We assessed patients in CS supported with Impella™ in two tertiary care centres over 62 months. UFH was titrated based on anti-Xa levels with parallel APTT measurements. In-range anti-Xa levels were considered between 0.20-0.30IU/mL or 0.31-0.50IU/mL and corresponding APTT levels were 40-55s and 56-80s, respectively. Pearson correlation was calculated between anti-Xa and APTT. Samples with in-range anti-Xa but prolonged APTT were analyzed for abnormalities in INR (≥1.5) and/or fibrinogen (<1.5g/l). Mortality during Impella™ support was then compared in those with and without additional coagulation abnormalities (Chi-square test).

Results: Correlation between anti-Xa and APTT was weak (r=0.50, p<0.001, N=2447). When anti-Xa in range (N=1914 samples), 24% had short, 52% had in-range, and 24% had prolonged corresponding APTT. Of 57 patients with prolonged APTT, 28 had abnormal same-day INR and/or fibrinogen, whereas 29 had normal fibrinogen and INR. Mortality was higher in patients with abnormal INR and/or fibrinogen compared to those with normal fibrinogen and INR (32% vs. 10%; p=0.043).

Conclusions: Anti-Xa/APTT-discrepancies are frequent during pMCS for CS, highlighting the importance of a multiple testing strategy. Outcomes of patients with prolonged APTT was related to the presence of abnormal INR and/or fibrinogen, suggesting serious concomitant underlying disease.