Welcome to Congress 2023 and the STAR research presentation. I will be presenting my research titled, Validation of Heparin-Induced Thrombocytopenia Risk Stratification Tools in Post-Surgical Cardiovascular Patients. My name is Sheraston Kokoi. In my current role, I am the Critical Care Pharmacy Fellow in the Vanderbilt-Lipscomb Critical Care Fellowship Training Program at the Critical Illness, Brain Dysfunction, and Survivorship Center, also known as the SIPP Center in Nashville, Tennessee. I am a Nashville native who graduated from Lipscomb University College of Pharmacy in 2021 with my doctorate of pharmacy and completed PGY-1 residency training at TriStar Centennial Medical Center. My area of interest is critical care with an emphasis on acute cardiovascular illnesses, sedation strategies, and delirium. This research was supported in whole or in part by HCA and or an HCA-affiliated entity. The views expressed in this publication represent those of the authors and do not necessarily represent the official views of HCA or any of its affiliated entities. The study authors have no personal or financial relationships to disclose. Learning objectives for this presentation include identifying risk factors for thrombocytopenia in this patient population, differentiating between the 4T, CPB, and HEP scoring tools, and determining which scoring tool you would utilize to risk stratify this population. Heparin-induced thrombocytopenia, or HIT, is an immune-mediated adverse event that occurs in approximately 0.1 to 3% of cardiovascular surgery patients. The 2012 CHESS guidelines recommend utilizing the 4T score to risk stratify patients, but this tool has only been validated in medical patients. The flowchart on the slide demonstrates a typical course for clinical suspicion of HIT. The two tests employed in a HIT workup are the enzyme-linked immunosorbent assay, or ELISA, and the serotonin release assay, or SRA. The ELISA is detecting IgG antibodies to heparin platelet factor 4 complexes and is the preliminary test in patients determined to be at an increased risk of HIT. This lab is highly sensitive but has a variable specificity. If the optical density is greater than 0.4, an SRA should be sent out as a confirmatory test. There is much debate regarding the optical density when it comes to the ELISA, as traditionally scores greater than 0.4 indicate a higher likelihood of HIT. Some sources point to greater than 1.0 as high risk, and some go as far as indicating 1.5 as high likelihood for HIT. The SRA is a functional assay that measures heparin-dependent platelet activation. Platelets are incubated and exposed to different concentrations of heparin. This exposure should stimulate the binding of IgG antibodies to the platelets, leading to the release of endogenous serotonin, and thus a positive result. The caveat with this lab is time because of the incubation period. It's important to consider other contributions to thrombocytopenia in patients post-CV surgery, although it is not uncommon for providers to focus on heparin exposure as the culprit. Specifically in our patient population, we find that continuous renal replacement therapy, or CRRT, medications, acute blood loss, mechanical circulatory support, or MCS, and cardiopulmonary bypass machine use to be concerning for thrombocytopenia, either due to sheer mechanical stress or from platelet sequestration in the circuits. Thinking back to the contributing factors of thrombocytopenia in our CV surgery patients, these factors are not considered in the 4T scoring tool, which has been deemed the gold standard in medical patients. The novel CPB score considers time on the cardiopulmonary bypass machine as a risk factor, and a score of 2 or more indicates high-risk patients. Like the CPB score, the HEP score looks at various contributors, but also factors that mitigate the risk of HIT as a source of thrombocytopenia. A score of 2 or more also indicates high-risk patients. We aim to investigate the implication of these scoring tools in our CV surgery patient population. Our study was a retrospective single-center cohort analysis, and the purpose was to compare the accuracy of the 4T, CPB, and HEP scoring tools to identify HIT in the surgical CV population. Our objective was to evaluate the impact of applying these scoring tools in post-surgical CV patients compared to the ELISA and or SRA results to accurately predict HIT. The primary endpoint of our study was the number of patients whose scoring tool prediction matched ELISA and SRA testing. Our secondary endpoints included the sensitivity and specificity of the scoring tools, the optical density cutoff correlated with HIT within our population, and the overall occurrence of thromboembolism. We included adults 18 years and older admitted to the CVICU or CCU with CB surgery, which was defined as a mitral valve replacement, a surgical aortic valve replacement, aortic dissection repair, or coronary artery bypass grafting. Non-CV surgery patients were excluded, as well as patients who required ECMO secondary to cardiogenic shock. 291 patients were identified by location of HIT lab testing, and we excluded 154 due to no CV surgery. A total of 137 patients were included and further characterized by HIT status. We defined HIT positive as either an ELISA optical density greater than 1, with evidence of thromboembolism, or a positive SRA. The higher optical density cutoff was chosen due to increasing literature indicating a cutoff of one or more being more specific for HIT. In total, 126 patients were HIT negative and 11 were HIT positive. Looking at the baseline characteristics, there was no difference in both groups overall. The average patient in our analysis was a 68-year-old white male with comorbid hypertension, whose primary CV surgery was a CABG. Notably, there was a trend towards a significantly longer length of stay in the ICU in our HIT positive arm. When assessing the primary endpoint of the number of patients who scored into a prediction matched ELISA and SRA testing, we found a significant difference when utilizing the 4T score, which was driven by the indication of high risk, indicated by a score greater than 6. Additionally, both the CPB and HEP scores demonstrated significance in predicting HIT with patients determined to be high risk. When assessing the secondary outcomes, the optical density associated with HIT in our population was a significant finding, with a median score of 1.28 in the HIT positive arm, which correlates with emerging literature indicating a higher cutoff holding a stronger positive predictive value. Both arterial and venous thromboembolism occurred more commonly in the HIT positive arm. Looking at the sensitivity and specificity of these two novel scoring tools, the CPB sensitivity was 33% compared to the HEP score, which was 100%. Whereas comparing the specificity, the CPB score was higher at 75% compared to the HEP scoring tool, which was 57%. In discussing some of the strengths, limitations, and conclusions of our analysis, it is a real-world analysis of novel scoring tools in a defined patient population. Additionally, there are limited publications comparing this data with similar outcomes, although we do acknowledge it is retrospective in nature and it is a small sample size from one cohort analysis. There are data inconsistencies within the electronic health record as well. But in conclusion, we would say the HEP scoring tool demonstrated high sensitivity and 100% specificity in identifying HIT in our patient population. An optical density greater than 1 is highly concerning for HIT and warrants great concern. Future opportunities include evaluating the impact of other contributors to thrombocytopenia and replicating this analysis on a larger scale to better validate the scoring tools. I would like to acknowledge and thank my research team for their guidance and assistance throughout this project. And I thank you for your interest and attendance to my presentation.

heparin-induced thrombocytopenia

risk stratification tools

post-surgical cardiovascular patients

4T score

HEP