The Journal of Heart and Lung Transplantation
International Society for Heart and Lung Transplantation.
(189)| Volume 40, ISSUE 4, SUPPLEMENT , S88, April 2021

A Modified 4Ts Score for Heparin-Induced Thrombocytopenia in the Mechanical Circulatory Support Population

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      Patients undergoing cardiac surgery are at increased risk for heparin-induced thrombocytopenia (HIT). The aim of this study was to identify risk factors and assess the morbidity and mortality associated with HIT in the mechanical circulatory support population. We present a modified “4TMCS” scoring system for this population of patients. MCS represents a “definite” cause of thrombocytopenia and the proposed 4TMCS score replaces the "other causes" category with “Type of mechanical circulatory support”.


      We performed analysis of patients who underwent cardiac surgery at Stanford University Medical Center between May 1, 2008 and December 31, 2016. Patients were categorized into three groups: 1) Control, patients with normal post-operative platelet count; 2) HIT(-), patients who developed thrombocytopenia and tested negative for HIT; and 3) HIT(+), patients who developed thrombocytopenia and tested positive for HIT. Independent predictors of post-operative HIT were evaluated, and a comparison of diagnostic accuracy between the 4Ts and 4TMCS probability scores was performed.


      We identified 5,314 patients eligible for analysis between 2008 and 2016. In total, 125/5314 (2.4%) patients were diagnosed with HIT, of which 75/5314 (1.4%) had clinical evidence of thrombosis. Overall, in-hospital mortality was 25.6%, 11.7%, and 1.5% in the HIT(+), HIT(-), and control groups, respectively (P < 0.001). HIT significantly increased post-operative complications, including arterial and venous thromboembolism, respiratory complications, renal failure, and sepsis. MCS was associated with a significantly increased risk for HIT, with an incidence of 5.9% in patients receiving MCS versus 1.9% in those without (P < 0.001). Area under the receiver operator curve (AUC) analysis demonstrated improved diagnostic accuracy of the 4TMCS score in MCS patients compared to the 4Ts alone (AUC = 0.83 versus 0.77, P < 0.05).


      Heparin-induced thrombocytopenia is associated with worse outcomes and increased morbidity and mortality in patients undergoing cardiac surgery. Patients receiving MCS may be at increased risk for development of post-operative HIT. Awareness of pre-operative patient risk factors and application of a modified 4TMCS probability score may allow for more accurate screening and treatment of HIT in the MCS population.