Incidence of heparin-induced thrombocytopenia in patients with temporary mechanical circulatory support devices.
Attar D, Lines B, McCarty M, Coba V, Lekura J, Smith Z, and To L. Incidence of heparin-induced thrombocytopenia in patients with temporary mechanical circulatory support devices. ASAIO Journal 2018; 64:78.
Introduction: Temporary mechanical circulatory support (MCS) devices are used for hemodynamic support in patients with cardiogenic shock. MCS devices are prone to thrombosis and require anticoagulation, often with unfractionated heparin. Heparin exposure and device related thrombocytopenia complicate the diagnosis of heparin-induced thrombocytopenia (HIT) and may lead to unnecessary treatment with direct thrombin inhibitors (DTI). To provide safe and effective care for patients with newly implanted MCS devices, the incidence of laboratory confirmed HIT needs to be further characterized. Objective: To determine the incidence of HIT in patients with newlyimplanted temporary MCS devices Study Design: Retrospective, cohort study Methods: This study included patients admitted to the cardiovascular intensive care unit with a newly-implanted temporary MCS device at Henry Ford Hospital from January 2014 to January 2017. MCS devices included in this study were extra-corporeal membrane oxygenation (ECMO) and Impella®. The primary endpoint was the incidence of laboratory confirmed HIT. Definite HIT was defined as a positive serotonin release assay (SRA) or heparin-induced platelet antibody assay (HIPA) with an optical density (OD) greater than or equal to 2. Probable HIT was defined as an OD between 1.01 and 1.99 +/-SRA intermediate, while possible HIT was defined as an OD between 0.41 and 1 +/-SRA intermediate. HIT negative was defined as an OD less than 0.4 or a negative SRA. Non-HIT related thrombocytopenia was defined as an absence of HIPA or SRA order. In cases where SRA and OD were both ordered but SRA interpretation conflicted with OD interpretation, HIT category was determined based on SRA due to this assay's greater sensitivity and specificity compared to HIPA. However, if SRA result was intermediate, then the likelihood of HIT was determined based on OD instead. Secondary endpoints include use of DTI such as argatroban in patients with unconfirmed HIT, incidence of HIT amongst each of the MCS devices, and utility of the 4T score, HIT Expert Probability (HEP) score, and Lillo-Le Louët model in predicting the presence of HIT. Categorical variables are presented as n (%). Continuous variables are presented as mean (standard deviation (SD)) or median (interquartile range), as appropriate. Results: A total of 182 cases with newly-implanted temporary MCS devices met inclusion criteria: 122 Impella® (67%) and 60 ECMO (33%). Diagnostic HIT assays were ordered in 43 of 182 cases (23.6%). In this population, 43 HIPA and 16 SRA assays were ordered. The median OD was 0.19 (0.11-0.52); two SRAs were positive and 14 were negative. Of the 182 cases, two had definite HIT (1.1%), zero had probable HIT, two had possible HIT (1.1%), and 39 were HIT negative (21.4%). The incidence of definite HIT was 1.7% (1/60) in the ECMO group and 0.82% (1/122) in the Impella® group. For patients with diagnostic HIT assays ordered, the 4T score sensitivity was 0.25 (0.01-0.78) and specificity was 0.79 (0.63-0.90). By comparison, the sensitivity of the HEP score was 0.50 (0.09-0.91) and specificity was 0.62 (0.45-0.76). Argatroban was administered to 16 patients with suspected HIT (37.21%) and was continued for an average of 6.25 days (SD 8.25); two of these patients were later determined to be HIT negative. Conclusion: Definite or probable HIT occurs infrequently with ECMO and Impella devices, yet over one-third of patients receive alternative anticoagulation despite being negative for HIT. Current HIT scoring systems failed to accurately screen for HIT in temporary support MCS devices and a modified MCS HIT scoring model is needed. Further analysis is needed to assess the implications of over-diagnosing HIT and the subsequent initiation of alternative anticoagulants.