Heparin-Induced Thrombocytopenia in Cardiac Surgery Patients

Risk factors and prediction model for thrombocytopenia following coronary artery bypass graft surgery in elderly Chinese population

Background

Thrombocytopenia, a common complication of coronary artery bypass graft (CABG) surgery, is particularly prevalent among elderly individuals. This study developed a risk prediction model utilizing preoperative and intraoperative variables to identify high-risk elderly patients prone to developing thrombocytopenia.

Methods

The patients were retrospectively recruited from Beijing Anzhen Hospital between February 2019 and December 2020. Postoperative thrombocytopenia was defined as a postoperative platelet (PLT) count <100×109/L as measured within 7 days after surgery. The entire population was randomly split into derivation and validation sets in a 7:3 ratio. The derivation set underwent variable screen by the least absolute shrinkage and selection operator (LASSO) regression method. To evaluate the predictive ability of the model for thrombocytopenia, decision curve analysis (DCA) and receiver operating characteristic (ROC) curves were generated in the derivation and validation sets.

Results

A total of 1,773 patients were recruited in this study, with random assignment to either the derivation set (1,242 cases) or the validation set (531 cases). LASSO regression was utilized the risk factors associated with thrombocytopenia, resulting in selection of preoperative baseline variables: body mass index (BMI), estimated glomerular filtration rate (eGFR), B-type natriuretic peptide (BNP), preoperative PLT, and use of beta-blocker, and intraoperative variables: red blood cell (RBC) transfusion, plasma transfusion, use of intra-aortic balloon pump (IABP) and cardiopulmonary bypass (CPB), reoperation for bleeding, washed RBC transfusion volume, and use of epinephrine. The logistic regression was employed to establish the risk prediction. The area under the ROC curve (AUC) for the derivation set was 0.900 [95% confidence interval (CI): 0.880-0.920], while for the validation cohort, it was 0.897 (95% CI: 0.866-0.928).

Conclusions

The model incorporating significant preoperative and intraoperative variables exhibited good predictive performance for thrombocytopenia in elderly patients undergoing CABG surgery.

Heparin-Induced Thrombocytopenia After Cardiac Surgery-A Statewide Review of Health Care Utilization

BACKGROUND

Despite its severe consequences, clinical and economic impacts of heparin-induced thrombocytopenia (HIT) after cardiac operations have not been well characterized. This study assessed statewide incidence, outcomes, and resource consumption associated with HIT after cardiac operations.

METHODS

This was a retrospective investigation of cardiac surgery patients using the Maryland Health Services Cost Review Commission's database from 2012 to 2020. Health care costs, utilization, and outcomes for those who experienced postoperative HIT were compared with propensity score-matched controls.

RESULTS

Of 33 583 cardiac surgery patients, 184 (0.55%) were diagnosed with postoperative HIT. Compared with non-HIT patients, HIT patients were significantly more likely to be in the oldest age group (>80 years; P < .001) and to have greater severity of illness at admission (P < .001). HIT was associated with a longer hospitalization (21 vs 7 days; P < .001), greater mortality (13.6% vs 2.3%; P < .001), and greater hospital charges ($123 160 vs $45 303; P < .001), even after propensity score matching. Readmission rates were not significantly different, however, and readmission hospital charges did not significantly differ between HIT and non-HIT patients.

CONCLUSIONS

In addition to worse outcomes, HIT was associated with higher costs during index admissions but not during readmissions of cardiac surgery patients. Strategies to minimize HIT could yield better outcomes and reduced costs, particularly relevant for health care systems seeking improved value-based care while reducing unnecessary hospitalizations.

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

OBJECTIVE

To identify risk factors and develop a pretest scoring system to differentiate patients with heparin-induced thrombocytopenia (HIT) in the mechanical circulatory support (MCS) population. The authors present a modified "4TMCS" scoring system, which considers the "type of mechanical circulatory support" that may help identify patients at risk for developing postoperative HIT.

DESIGN

A retrospective cohort study. Patients who underwent cardiac surgery were categorized into 3 groups: (1) normal platelet count, (2) thrombocytopenia with a negative HIT test, and (3) thrombocytopenia with a positive HIT test. A comparison of diagnostic accuracy between the 4Ts and 4TMCS probability scores was performed.

SETTING

At a single adult tertiary-care center.

PARTICIPANTS

A total of 5,314 patients who underwent cardiac surgery between May 1, 2008 and December 31, 2016.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

In total, 125 out of 5,314 patients (2.4%) were diagnosed with HIT, of whom 75 out of 5,314 (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). Mechanical circulatory support 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 compared with the 4Ts (AUC = 0.83 v 0.77, p < 0.044). The 4TMCS score had higher sensitivity than the 4Ts, using the guideline-recommended score cutoff of ≥4 (95.2% v 85.7%).

CONCLUSION

Heparin-induced thrombocytopenia is associated with worse outcomes and increased morbidity and mortality in the MCS population. Awareness of patient risk factors and the application of a modified 4TMCS probability score may allow for more accurate screening and treatment of HIT in the MCS population.

Does heparin rebound lead to postoperative blood loss in patients undergoing cardiac surgery with cardiopulmonary bypass?

BACKGROUND

Heparin rebound is a common observed phenomenon after cardiac surgery with CPB and is associated with increased postoperative blood loss. However, the administration of extra protamine may lead to increased blood loss as well. Therefore, we want to investigate the relation between heparin rebound and postoperative blood loss and the necessity to provide extra protamine to reverse heparin rebound.

METHODS

We searched PubMed, Cochrane, EMBASE, Google Scholar and Web of Science to review the question: "Does heparin rebound lead to postoperative blood loss in patients undergoing cardiac surgery with cardiopulmonary bypass." Combination of search words were framed within four major categories: heparin rebound, blood loss, cardiac surgery and cardiopulmonary bypass. All studies that met our question were included. Quality assessment was performed using the Cochrane risk of bias (RoB2) tool for randomized controlled trials and the risk of bias in non-randomized studies of intervention (ROBINS-I) for non-randomised trials.

RESULTS

4 randomized and 17 non-randomized studies were included. The mean incidence of heparin rebound was 40%. The postoperative heparin levels, due to heparin rebound, were often below or equal to 0.2 IU/mL. We could not demonstrate an association between heparin rebound and postoperative blood loss or transfusion requirements. However the quality of evidence was poor due to a broad variety of definitions of heparin rebound, measured by various coagulation tests and studies with small sample sizes.

CONCLUSION

The influence of heparin rebound on postoperative bleeding seems to be negligible, but might get significant in conjunction with incomplete heparin reversal or other coagulopathies. For that reason, it might be useful to get a picture of the entire coagulation spectrum after cardiac surgery, as can be done by the use of a viscoelastic test in conjunction with an aggregometry test.

Development of the Modern Cardiothoracic Intensive Care Unit and Current Management

The modern cardiothoracic intensive care unit (CTICU) developed as a result of advances in critical care, cardiology, and cardiac surgery. Patients undergoing cardiac surgery today are sicker, frailer, and have more complex cardiac and noncardiac morbidities. CTICU providers need to understand postoperative implications of different surgical procedures, complications that can occur in CTICU patients, resuscitation protocols for cardiac arrest, and diagnostic and therapeutic interventions such as transesophageal echocardiography and mechanical circulatory support. Optimum CTICU care requires a multidisciplinary team with collaboration between cardiac surgeons and critical care physicians with training and experience in the care of CTICU patients.

Heparin-induced thrombocytopenia: An illustrated review

Heparin-induced thrombocytopenia (HIT) is an immune-mediated adverse drug effect from unfractionated or low-molecular-weight heparin that results in thrombocytopenia and potentially catastrophic thrombosis. HIT occurs due to the development of platelet-activating antibodies against multimolecular complexes of platelet factor 4 and heparin. Given the frequency of thrombocytopenia and heparin use among hospitalized patients, calculation of the 4Ts Score is recommended to identify patients at increased likelihood of HIT and direct further evaluation. In patients with an intermediate or high probability 4Ts Score, an immunoassay and functional assay are recommended to confirm or refute the diagnosis of HIT. Heparin avoidance and initiation of nonheparin anticoagulation are the mainstays of acute HIT management. In this illustrated review, we provide visual summaries of the diagnosis and management of HIT, highlighting connections between pathophysiology and clinical care as well as summarizing efforts in quality improvement in the field. We further emphasize common pitfalls and pearls in diagnosis and management to encourage evidence-based care. We include graphical representation of the unique challenges of HIT with cardiopulmonary bypass and also delineate autoimmune HIT and its subtypes.

Modulation of ultralarge immune complexes in heparin-induced thrombocytopenia

BACKGROUND

Heparin-induced thrombocytopenia (HIT) is a serious thrombotic disorder caused by ultralarge immune complexes (ULICs) containing platelet factor 4 (PF4) and heparin that form the HIT antigen, together with a subset of anti-PF4 antibodies. ULICs initiate prothrombotic responses by engaging Fcγ receptors on platelets, neutrophils, and monocytes. Contemporary anti-thrombotic therapy for HIT is neither entirely safe nor entirely successful and acts downstream of ULIC formation and Fcγ receptor-initiated generation of thrombin.

OBJECTIVES

To determine whether HIT antigen and ULIC formation and stability could be modified favorably by inhibiting PF4-heparin interactions with fondaparinux, together with blocking formation of PF4 tetramers using a humanized monoclonal anti-PF4 antibody (hRTO).

METHODS

Results: The combination of fondaparinux and hRTO inhibited HIT antigen formation, promoted antigen dissociation, inhibited ULIC formation, and promoted ULIC disassembly at concentrations below the effective concentration of either alone and blocked Fcγ receptor-dependent induction of factor Xa activity by monocytic THP1 cells and activation of human platelets in whole blood. Combined with hRTO, fondaparinux inhibited HIT antigen and immune complex formation and activation through Fcγ receptors at concentrations at or below those used clinically to inhibit FXa coagulant activity.

CONCLUSIONS

HIT antigen and immune complexes are dynamic and amenable to modulation. Fondaparinux can be converted from an anticoagulant that acts at a downstream amplification step into a rationale, disease-specific intervention that blocks ULIC formation. Interventions that prevent ULIC formation and stability might increase the efficacy, permit use of lower doses, shorten the duration of antithrombotic therapy, and help prevent this serious thrombotic disorder.

Evaluation of Latex Immunoturbidimetric Assay Thresholds and HIT in Cardiothoracic Surgery

BACKGROUND

Heparin-induced thrombocytopenia (HIT) is a common differential diagnosis in cardiothoracic surgery. The latex immunoturbidimetric assay (LIA) is an enhanced immunoassay that has recently been introduced for the detection of total HIT immunoglobulin and retains a higher specificity of 95% compared to the enzyme-linked immunosorbent assay.

OBJECTIVES

To investigate if a semiquantitative relationship exists between increasing LIA levels beyond the current positivity threshold and its correlation to positive serotonin release assay results in cardiothoracic surgery.

METHODS

This was a multicenter, observational cohort of cardiothoracic surgery patients initiated on anticoagulation with heparin-based products. To conduct sensitivity and specificity analysis of LIA values, HIT positive was defined as a LIA value ≥1 unit/mL and HIT negative was defined as a LIA level <1 unit/mL. A receiver operating characteristic (ROC) analysis was utilized to evaluate the predictive performance of the LIA.

RESULTS

At manufactures' cutoffs of ≥1.0 unit/mL, LIA sensitivity and specificity was 93.8% and 22%, respectively, yielding a false positive rate of 78%. At a higher cutoff of 4.5 units/mL, LIA sensitivity and specificity was 75% and 71%, respectively, yielding a false positive rate of 29% and an area under the ROC curve of 0.75 (P = .01; 95% confidence interval: 0.621-0.889). Bivalirudin was initiated in 84.6% of false positive LIA results.

CONCLUSION

This study suggests that the diagnostic accuracy of the LIA can be optimized by increasing the LIA positivity threshold. Proposing a higher LIA cutoff, may mitigate unwarranted anticoagulation and bleeding outcomes.

Cardiopulmonary Bypass Surgery in a Patient with Unexpected Heparin-Induced Thrombocytopenia

We report a case of a 77-year-old woman with massive pulmonary embolism associated with heparin-induced thrombocytopenia. Before developing a pulmonary embolism, the patient underwent gastrectomy due to gastric cancer and received subcutaneous heparin calcium for deep venous thrombosis prophylaxis for 5 d. Then, thrombectomy with cardiopulmonary bypass using full heparinization was successfully performed. The patient was definitively diagnosed with this condition postoperatively, based on elevated serum antibody levels, in addition to pre- and postoperative thrombocytopenia and thrombosis. Intravenous heparin therapy was switched to argatroban. Although it is uncommon, clinicians should consider this condition in patients with a history of heparin exposure.

Temporal presentations of heparin-induced thrombocytopenia following cardiac surgery: A single-center, retrospective cohort study

BACKGROUND

Heparin-induced thrombocytopenia (HIT) is an important adverse drug reaction that can occur postcardiac surgery. Preoperative exposure to unfractionated heparin (UFH) is common, raising the issue of how frequently cardiac surgery-associated HIT occurs after immunizing preoperative exposure to heparin.

OBJECTIVE

To determine the frequency and clinical picture of HIT occurring within 4 days of cardiac surgery (early presentation) versus later presentations (typical, delayed).

METHODS

We identified patients with laboratory-confirmed HIT following cardiac surgery over 30 years in a single cardiac surgery center. Three different clinical presentations of HIT were identified: typical (HIT-related platelet count fall beginning between postoperative days [PODs] 5-10), delayed (patients with falls after POD10 or who presented following hospital discharge), and early (established before POD5, including during cardiac surgery [acute intraoperative HIT]).

RESULTS

Of 129 patients identified with HIT complicating cardiac surgery, 100 had typical and 16 had delayed presentation of HIT; only 13 patients (10.1%) presented with early HIT, all of whom had received exposure to UFH during the 10 days before cardiac surgery. No patient was identified in whom remote preoperative UFH exposure was implicated in explaining early HIT. Notably, five patients appeared to have had acute intraoperative HIT, without immediate adverse consequences.

CONCLUSIONS

Approximately 90% of patients with HIT after cardiac surgery appear to develop this complication due to immunization triggered by cardiac surgery; however, in approximately 10% of patients, early presentation during the first four PODs (or intraoperatively) can be explained by recent immunizing exposure to heparin.

A Review of Direct-acting Oral Anticoagulants and Their Use in Solid Organ Transplantation

Direct-acting oral anticoagulant (DOAC) use has increased dramatically since their introduction because of the growing evidence of proven efficacy and enhanced safety compared with warfarin and the low-molecular-weight heparins in the general population. Unfortunately, there is a dearth of quality data regarding the safety and efficacy of the DOACs in patients awaiting organ transplant and those who received a solid organ transplant. This review aims to evaluate the available literature and considerations regarding anticoagulation use in transplant recipients, focusing on preoperative, perioperative, and postoperative DOAC use.

Non-heparin-induced thrombocytopenia in patients after open-heart surgery

BACKGROUND

Thrombocytopenia (platelet count below 150 x 10³/μL) is a common finding after open-heart surgery and can lead to various complications, including patient death. This study aimed to determine the extent of non-heparin-induced thrombocytopenia in open-heart surgery and to highlight the associated factors.

MATERIALS AND METHODS

In this cohort study, 842 patients who underwent valve and/or coronary bypass surgery over a 5-year period were retrospectively analyzed. After open-heart surgery, patients whose platelet count was less than 150 x 10³/μL on a complete blood count 12 and 24 h after surgery were classified as thrombocytopenic. Three hundred twenty patients without thrombocytopenia and 21 patients with a high probability of heparin-induced thrombocytopenia were excluded from the study. Logistic regression analysis was used to assess the association of independent variables in moderate-severe thrombocytopenia: Age groups, sex, underlying disease, symptoms, type of surgery, pump time, pulsatile or non-pulsatile duration, degree of hypothermia, hemodilution, oxygenator type, use of an intra-aortic balloon, and erythrocyte transfusion counts were included in the analysis.

RESULTS

A total of 501 patients were diagnosed as having non-heparin-induced thrombocytopenia, and 64.3% were male. Three hundred seventy-seven (75.2%) patients had mild thrombocytopenia and 124 (24.7%) had moderate-severe thrombocytopenia. The postoperative platelet count was significantly lower than the preoperative platelet count (213 x 10³ vs.117 x 10³/μL; p < 0.001). Moderate-severe thrombocytopenia was associated with age ≥80 years odds (OR = 9.026, 95% CI: [1.757-46.363]; p = 0.008), isolated valve surgery (OR = 3.090, 95% CI: [1.867-5.114]; p < 0.001), and valve surgery with coronary bypass (OR = 4.938, 95% CI: [1.638-14.889]; p = 0.005) compared to isolated coronary bypass, type of oxygenator (Nipro vital compared with Affinity OR = 11.097, 95% CI: [1.923-64.023]; p = 0.007), erythrocyte transfusion count (OR = 1.219, 95%CI: [1.046-1.420]; p = 0.011).

CONCLUSION

Age 80 years or older, surgical procedures including heart-valve surgery, and the number of red blood cell transfusions are associated with the risk of moderate-to-severe thrombocytopenia. This study provides a guide in terms of risk factors that may lead to moderate-to-severe thrombocytopenia after open-heart surgery. However, future multicentre prospective randomized studies may provide more detailed information on this subject.

Heparin-induced thrombocytopenia and thrombosis in primary lymphedema patients who underwent vascularized lymph node transplantations

BACKGROUND

Heparin-induced thrombocytopenia and thrombosis (HITT) may result in microsurgical flap failure. This study investigated the outcomes of HITT in primary lymphedema patients who underwent vascularized lymph node transplantations (VLNT).

METHODS

Between 2012 and 2019, primary lymphedema patients who underwent VLNTs were retrospectively included. The 4Ts score was used to categorize patients into HITT (scores of 5-7) and non-HITT (score < 5) groups. Outcome evaluations included the re-exploration rate, success rate, circumferential differences, cellulitis episodes, and Lymphedema Specific Quality of Life Questionnaire (LYMQoL) scores.

RESULTS

Twenty-six and 15 patients with 31 and 16 VLNTs were included in the HITT and non-HITT groups, respectively. The HITT group had significantly greater first, second and third re-exploration rates of 38.7% (12/31), 25.7% (8/31), and 6.5% (2/31) than the non-HITT group (6.3%, 0%, and 0%, all p < 0.01), respectively. The platelet counts significantly decreased by 21.0% in the HITT group compared with the non-HITT group (14%) on postoperative Day one (p < 0.01) with a cutoff value of 17% and AUC = 0.88.

CONCLUSIONS

HITT may cause a high re-exploration rate of VLNTs in primary lymphedema patients. The 17% reduction in platelets on postoperative day one was an early sign for detecting HITT.

Cardiac transplantation after heparin induced thrombocytopenia: A systematic review

PURPOSE

Heparin induced thrombocytopenia (HIT) presents a unique challenge in patients requiring orthotopic heart transplantation (OHT). We sought to pool the existing evidence in a systematic review.

METHODS

Electronic search was performed to identify all relevant studies on OHT in patients with HIT. Patient-level data for 33 patients from 21 studies were extracted for statistical analysis.

RESULTS

Median patient age was 51 [41, 55] years, with 75.8% (25/33) males. All patients had a clinical diagnosis of HIT, and anti PF4/Heparin antibodies were positive in 87.9% (29/33). Median lowest reported platelet count was 46 × 10⁹ /L [27.2, 73.5]. Intraoperatively, 61% (20/33) of patients were given unfractionated heparin (UFH), while 39% (13/33) were given alternative anticoagulants. The alternative agent subgroup required more antifibrinolytics [54% (7/13) vs. 10% (2/20), p = 0.02] and clotting factors [69.2% (9/13) vs. 15.0% (3/20) p<0.01]. Peri-operative thrombosis occurred more in [53.8% (7/13) vs 0% (0/20, p<0.01) alternate agent subgroup. More patients in the alternate agent subgroup required post-operative transfusions [54% (7/13) vs. 0% (0/20), p<0.01]. Thirty-day mortality of 15.2% (5/33) was comparable between the subgroups.

CONCLUSION

Heparin use during OHT may be associated with less adverse effects compared to use of other anticoagulants with no difference in 30-day mortality. This article is protected by copyright. All rights reserved.

Heparin-induced thrombocytopenia and cardiovascular surgery

Clinicians generally counsel patients with a history of heparin-induced thrombocytopenia (HIT) to avoid heparin products lifelong. Although there are now many alternative (nonheparin) anticoagulants available, heparin avoidance remains challenging for cardiac surgery. Heparin is often preferred in the cardiac surgery setting based on the vast experience with the agent, ease of monitoring, and reversibility. To "clear" a patient with a history of HIT for cardiac surgery, hematologists must first confirm the diagnosis of HIT, which can be challenging due to the ubiquity of heparin exposure and frequency of thrombocytopenia in patients in the cardiac intensive care unit. Next, the "phase of HIT" (acute HIT, subacute HIT A/B, or remote HIT) should be established based on platelet count, immunoassay for antibodies to platelet factor 4/heparin complexes, and a functional assay (eg, serotonin release assay). As long as the HIT functional assay remains positive (acute HIT or subacute HIT A), cardiac surgery should be delayed if possible. If surgery cannot be delayed, an alternative anticoagulant (preferably bivalirudin) may be used. Alternatively, heparin may be used with either preoperative/intraoperative plasma exchange or together with a potent antiplatelet agent. The optimal strategy among these options is not known, and the choice depends on institutional experience and availability of alternative anticoagulants. In the later phases of HIT (subacute HIT B or remote HIT), brief intraoperative exposure to heparin followed by an alternative anticoagulant as needed in the postoperative setting is recommended.

Heparin-Induced Thrombocytopenia under Mechanical Circulatory Support by Large Impella for Acute Cardiogenic Shock

Despite the critical feature of heparin-induced thrombocytopenia (HIT) for patients on mechanical circulatory support, reports on its incidence and outcome are still scarce. Thus, we report on clinical features of HIT in patients under Impella 5.0 or 5.5 (Abiomed Inc., Danvers, MA, USA) (Impella 5+) support for acute cardiogenic shock (CS) by focusing on observed thrombotic events. Between November 2018 and December 2020, a total of 56 consecutive patients were enrolled in a single-center retrospective study. A total of 21 patients (37.5%) were tested for HIT, and 6 (10.7%) proved positive for HIT at 10.5 ± 2.89 days after the first heparin administration during current admission. Interestingly, thrombocyte counts dropped under Impella support in all groups (all cases, no HIT test, and HIT negative group: p < 0.001, HIT-positive group: p = 0.001). All HIT-positive patients were switched from heparin to argatroban. HIT-associated thrombotic events were observed in two cases resulting in Impella dysfunction due to pump thrombosis (n = 1) and left ventricular (LV) thrombus formation (n = 1). Under large Impella support, the prevalence of HIT was relatively high. Further, thrombocytopenia does not deliver a high specificity in the setting of Impella 5+ support. Considering HIT manifestation, a routine HIT test may be considered to avoid critical thrombotic adverse events.

Screening and diagnosis of heparin-induced thrombocytopenia in the pediatric population: A tertiary centre experience

INTRODUCTION

Heparin-induced thrombocytopenia (HIT) is a life-threatening side effect of heparin necessitating immediate heparin discontinuation. A missed diagnosis of HIT carries significant morbidity and mortality, while overdiagnosis may result in unnecessary and potentially harmful use of alternative anticoagulants in the pediatric population. We aimed to determine the proportion of HIT screening tests at our pediatric tertiary care centre ultimately leading to a diagnosis of HIT by functional assay (either lumi-aggregometry or serotonin-release assay). We hypothesized that the frequency of HIT at our centre would be lower than that reported in the literature.

MATERIALS AND METHODS

We conducted a retrospective review including children aged 0 to 18 years who had HIT testing performed at our centre between 2010 and 2018 (N = 189; 51% female). A screening enzyme immunoassay, if positive, is followed by a functional assay which must be positive to establish the diagnosis of HIT. Data were analyzed to establish trends in demographic and clinical features of patients with a positive HIT screening test. Our primary outcome was the rate of HIT confirmed by functional testing amongst children screened for HIT from 2010 to 2018.

RESULTS AND CONCLUSIONS

There were 233 screening tests performed on 189 distinct patients. Only one patient (0.4%) received a diagnosis of HIT based on functional assay. This patient was a 16-year-old female later found to have a JAK2 mutation. The false positive rate of the enzyme immunoassay was 9.4% (N = 22). There were no positive enzyme immunoassay tests in the neonatal age group (N = 49). These results reinforce that HIT is rare in children.

Heparin-Induced Thrombocytopenia in Iranian Cardiac Surgery Patients Using the 4Ts Clinical Scoring System and Laboratory Methods

Background: Heparin-induced thrombocytopenia (HIT) is a serious adverse drug reaction. HIT diagnosis needs an algorithmic approach including clinical evaluation and laboratory tests (screening and confirmatory). Few studies have been conducted on HIT in Iran, and most existing research has been general and based on clinical evaluations alone. The present study was conducted to determine the prevalence of HIT among cardiac surgery patients using an algorithmic approach.

Materials and Methods: A cross-sectional study was carried out over a period of 10 months, at Modares Hospital (Tehran, Iran) on 92 patients who were candidates for cardiac surgery. For the clinical evaluation, the 4Ts scoring system was used; in cases with 4Ts scores ≥4, a laboratory evaluation of anti-PF4/heparin antibody (Ab) was performed by enzyme-linked immunosorbent assay (ELISA) and a HIPA test too as a functional confirmatory method. The patients with 4Ts scores ≥4 who were ELISA positive (OD ≥0.2) and HIPA positive were taken as a definite case of HIT.

Results: Of the 92 patients who had undergone cardiac surgery, 14 (15%) had 4Ts scores ≥4. Anti- PF4/heparin Ab was detected in eight patients using the ELISA and in six patients using the HIPA. Ultimately, definite HIT was confirmed in five of the patients.

Conclusion: The prevalence of HIT was 5.4% among the cardiac surgery patients assessed in the present study. To the researchers’ knowledge, this is the first time that HIT has been evaluated in Iran using a comprehensive algorithmic approach including clinical history-taking and both immunological and functional laboratory tests, and the findings showed a slightly higher HIT frequency in this single-center study in comparison with the other studies carried out in other countries.

Comparison of Clinical Scoring Tools to Predict Heparin-Induced Thrombocytopenia in Cardiac Surgery

The 4Ts and HIT-Expert Probability (HEP) scoring tools for heparin-induced thrombocytopenia (HIT) have not been validated in cardiac surgery patients, and the reported sensitivity and specificity of the Post-Cardiopulmonary Bypass (CPB) scoring tool vary widely in the 2 available analyses. It remains unclear which of the available scoring tools most accurately predicts HIT in this population. Forty-nine HIT-positive patients who underwent on-pump cardiac surgery within a 6-year period were loosely matched to 98 HIT-negative patients in a 1:2 case-control design. The 4Ts, HEP, and CPB scores were calculated for each patient. Sensitivity and specificity of each tool were calculated using standard cut-offs. The Youden method was utilized to determine optimal cut-offs within receiver operating characteristic (ROC) curves of each score, after which sensitivities and specificities were recalculated. Using standard cut-offs, the sensitivities for the CPB, HEP, and 4Ts scores were 100%, 93.9%, and 69.4%, respectively. Specificities were 51%, 49%, and 71.4%, respectively. The AUC of the scoring tool ROC curves were 0.961 for the CPB score, 0.773 for the HEP score, and 0.805 for the 4Ts score. Using the Youden method-derived optimal cut-off of  ≥3 points on the CPB score, sensitivity remained 100% with improved specificity to 88.9%. The CPB score is the preferred HIT clinical scoring tool in adult cardiac surgery patients, whereas the 4Ts score performed less effectively. A cut-off of ≥ 3 points on the CPB score could increase specificity while preserving high sensitivity, which should be validated in a prospective evaluation.

Serotonin-release assay-positive but platelet factor 4-dependent enzyme-immunoassay negative: HIT or not HIT?

IgG-specific and polyspecific PF4-dependent enzyme-immunoassays (EIAs) have exceptionally high sensitivity (≥99%) for diagnosis of heparin-induced thrombocytopenia (HIT), a drug reaction caused by platelet-activating antibodies detectable by serotonin-release assay (SRA). The IgG-specific EIAs are recommended for screening, as their high sensitivity is accompanied by relatively high specificity vis-à-vis polyspecific EIAs. We investigated the frequency of SRA-positive/EIA-negative (SRA+/EIA-) HIT, prompted by referral to our reference HIT laboratory of serial blood samples from a patient ("index case") with false-negative IgG-specific EIAs. Despite initial clinical suspicion for HIT, repeat negative IgG-specific EIAs prompted heparin resumption, which triggered recurrent thrombocytopenia and near-fatal cardiac arrest, indicating likely post-heparin HIT-associated anaphylactoid reaction. Further investigations revealed a strong-positive SRA, whether performed with heparin alone, PF4 alone, or PF4/heparin, with inhibition by Fc receptor-blocking monoclonal antibody (indicating IgG-mediated platelet activation); however, five different IgG-specific immunoassays yielded primarily negative (or weak-positive) results. To investigate the frequency of SRA+/EIA- HIT, we reviewed the laboratory and clinical features of patients with this serological profile during a 6-year period in which our reference laboratory investigated for HIT using both SRA and IgG-specific EIA. Although ~0.2% of 8546 patients had an SRA+/EIA- profile, further review of 15 such cases indicated clerical/laboratory misclassification or false-positive SRA in all, with no SRA+/EIA- HIT case identified. We conclude that while SRA+/EIA- HIT is possible-as shown by our index case-this clinical picture is exceptionally uncommon. Moreover, the requirement for a positive EIA is a useful quality control maneuver that reduces risk of reporting a false-positive SRA result.

High-Dose Dabigatran Is an Effective Anticoagulant for Simulated Cardiopulmonary Bypass Using Human Blood

BACKGROUND

Currently no ideal alternative exists for heparin for cardiopulmonary bypass (CPB). Dabigatran is a direct thrombin inhibitor for which a reversal agent exists. The primary end point of the study was to explore whether Dabigatran was an effective anticoagulant for 120 minutes of simulated CPB.

METHODS

The study was designed in 2 sequential steps. Throughout, human blood from healthy donors was used for each experimental step. Initially, increasing concentrations of Dabigatran were added to aliquots of fresh whole blood, and the anticoagulant effect measured using kaolin/tissue factor-activated thromboelastography (rapidTEG). The dynamics of all thromboelastography (TEG) measurements were studied with repeated measures analysis of variance (ANOVA). Based on these data, aliquots of blood were treated with high-concentration Dabigatran and placed in a Chandler loop as a simple ex vivo bypass model to assess whether Dabigatran had sufficient anticoagulant effects to maintain blood fluidity for 2 hours of continuous contact with the artificial surface of the PVC tubing. Idarucizumab, humanized monoclonal antibody fragment, was used to verify the reversibility of Dabigatran effects. Finally, 3 doses of Dabigatran were tested in a simulated CPB setup using a heart-lung machine and a commercially available bypass circuit with an arteriovenous (A-V) loop. The primary outcome was the successful completion of 120 minutes of simulated CPB with dabigatran anticoagulation, defined as lack of visible thrombus. Thromboelastographic reaction (R) time was measured repeatedly in each bypass simulation, and the circuits were continuously observed for clot. Scanning Electron Microscopy (SEM) was used to visualize fibrin formation in the filters meshes during CPB.

RESULTS

In in vitro blood samples, Dabigatran prolonged R time and reduced the dynamics of clot propagation (as measured by speed of clot formation [Angle], maximum rate of thrombus generation [MRTG], and time to maximum rate of thrombus generation [TMRTG]) in a dose-dependent manner. In the Chandler Loop, high doses of Dabigatran prevented clot formation for 120 minutes, but only at doses higher than expected. Idarucizumab decreased R time and reversed anticoagulation in both in vitro and Chandler Loops settings. In the A-V loop bypass simulation, Dabigatran prevented gross thrombus generation for 120 minutes of simulated CPB.

CONCLUSIONS

Using sequential experimental approaches, we showed that direct thrombin inhibitor Dabigatran in high doses maintained anticoagulation of blood for simulated CPB. Idarucizumab reduced time for clot formation reversing the anticoagulation action of Dabigatran.

GTH 2021 State of the Art-Cardiac Surgery: The Perioperative Management of Heparin-Induced Thrombocytopenia in Cardiac Surgery

Heparin-induced thrombocytopenia (HIT) is a severe, immune-mediated, adverse drug reaction that paradoxically induces a prothrombotic state. Particularly in the setting of cardiac surgery, where full anticoagulation is required during cardiopulmonary bypass, the management of HIT can be highly challenging, and requires a multidisciplinary approach. In this short review, the different perioperative strategies to run cardiopulmonary bypass will be summarized.

Clinical validation of immunoassay HemosIL® AcuStar HIT-IgG (PF4-H) in the diagnosis of Heparin-induced thrombocytopenia

Heparin induced thrombocytopenia (HIT) is a life and limb-threatening complication of heparin exposure. The misdiagnosis of this disease can have major consequences on the patients. The objective of this study was to evaluate a diagnostic strategy that combines the 4Ts score with the result of HemosIL® AcuStar HIT-IgG (PF4-H) to confirm the diagnosis of HIT. Citrated plasmas from 1300 patients with suspicion of HIT were analyzed with a fully automated quantitative chemiluminescent immunoassay (HemosIL® AcuStar HIT-IgG (PF4/H)). If the IgG anti-PF4/H antibodies were positive (cut-off, 1 U/mL), HIT diagnosis was confirmed using functional tests. In total, 1300 samples of consecutive patients were enrolled, 94 (7.2%) of which gave positive results in HemosIL® AcuStar-IgG. HIT was diagnosed in 65 out of these patients, corresponding to a prevalence of 5%. Using ROC curve analysis, patients were divided into three groups according to their titer of antibodies. Higher values of the IgG (PF4-H) were associated with increased probability of HIT, and the diagnostic specificity was greatly increased using the combination of a 4Ts score > 3 and a positive titer ≥ 3.25 U/mL. Importantly, the diagnostic specificity is 100% when the titer is > 12.40 U/mL. We demonstrated that higher values of Anti PF4/H Antibodies were associated with a high probability of having HIT. A titer of HemosIL® IgG (PF4-H) > 12.40 U/mL has a specificity of 100% which should no require a functional test to confirm the diagnosis of HIT.

Positive Heparin/PF4 Antibodies and High Mortality Rate: a Retrospective Case-Series Analysis

Introduction

Heparin-induced thrombocytopenia (HIT) is a potentially lethal complication of unfractionated or low-molecular weight heparin therapy. We aimed to determine the incidence and mortality rate of patients with positive heparin/platelet factor 4 (PF4) antibodies, which is a rapid detection test of HIT.

Methods

Coronary artery bypass grafting and mitral and aortic valve surgeries were evaluated. Cardiopulmonary bypass was employed in all patients. The diagnosis of HIT was based on immunological assays. Postoperative complications, mortality rates, and the causes of death were specified in patients with positive heparin/PF4 antibodies.

Results

Postoperative thrombocytopenia was detected in 257 patients. Twenty of these patients undergoing open heart surgery were included in the final analysis. Antibodies against heparin/PF4 complex were positive in 20 patients. The mean body mass index was 28.8±2.3 kg/m², mean value of left ventricular ejection fraction was 48.3±6.7%, cardiopulmonary bypass time was 113.0±35.0 min, aortic cross-clamping time was 88.0±32.7 min, mean intensive care unit length of stay was 10.9±4.9 days, mean preoperative platelet count was 307.250±88528 platelets/microliter, and mean postoperative platelet count was 243.050±89.354 platelets/microliter. The mean duration of heparin exposure was 6.9±2.9 days. The mortality rate was 45% (nine patients) and 1.2% (three patients) in heparin/PF4 complex positive and negative patients, respectively.

Conclusion

Although the incidence of HIT was low in patients undergoing open heart surgery, an increased rate of early mortality was observed in patients with positive heparin/PF4 antibodies.

Association of Heparin Dose, Route, Timing, and Duration With Heparin-Induced Thrombocytopenia

BACKGROUND

The prevalence of heparin-induced thrombocytopenia (HIT) varies by population and the type and duration of heparinoid exposure; however, the association with unfractionated heparin (UFH) dose, route, timing, and duration has not been evaluated in cardiac surgery patients.

METHODS

A retrospective case-control study matched HIT-positive adult cardiac surgery patients (positive platelet factor 4 immunoglobulin G and serotonin release assays) 1:1 with HIT-negative controls. Total UFH dose, route, timing, and duration were compared between groups.

RESULTS

The study included 124 patients, 92 male (74%), with mean age of 65 ± 11 years. Significantly more HIT-positive patients received intravenous UFH preoperatively or postoperatively compared with patients without HIT (55 [88.7%] vs 23 [37.1%]; P < .001). There were no significant differences regarding intraoperative or subcutaneous UFH dose or duration. When controlling for obesity and cardiopulmonary bypass duration using multivariable conditional logistic regression, the odds of HIT were increased 10-fold in patients who received preoperative or postoperative intravenous UFH continuous infusion (odds ratio 10.2, 95% confidence interval, 3.1 to 33.7; P < .001). Receiver-operating characteristic curves demonstrated that receiving preoperative or postoperative intravenous UFH infusion total dose greater than 32,000 units (sensitivity 82%, specificity 74%, area under the curve 0.78) or longer than 7 hours (sensitivity 87%, specificity 68%, area under the curve 0.77) was associated with HIT.

CONCLUSIONS

Odds of HIT were increased 10-fold in adult cardiac surgery patients receiving preoperative or postoperative intravenous UFH infusion. Intraoperative UFH dose and subcutaneous route were not associated with HIT. Future study should evaluate incorporation of intravenous UFH administration, dose, and duration in HIT scoring tools for cardiac surgery patients.

How would we treat our own heparin-induced thrombocytopenia during cardiac surgery?

The aim of this article is to provide a comprehensive review of the current state of knowledge on heparin-induced thrombocytopenia (HIT) in cardiac surgery. The management of HIT patients undergoing cardiac surgery with cardiopulmonary bypass is complex and requires an interdisciplinary and patient-tailored approach because available evidence is limited and current anticoagulation strategies have potential risks. An index case is used to discuss both the established and new perioperative therapeutic options in HIT patients undergoing urgent cardiac surgery with cardiopulmonary bypass.

Association between the HLA-DRB1*03:01-DQB1*02:01 haplotype and PF4/heparin antibodies

HLA-DRB1*03:01-DQB1*02:01 haplotype patients develop higher anti–platelet factor 4/heparin (PF4/H) levels following IV heparin exposure. HLA-restricted antigen presentation may play a role in the formation of anti-PF4/H antibodies.

Heparin-induced thrombocytopenia (HIT): Review of incidence, diagnosis, and management

Heparin-induced thrombocytopenia (HIT) is a life and limb-threatening complication of heparin exposure. Here, we review the pathogenesis, incidence, diagnosis, and management of HIT. The first step in thwarting devastating complications from this entity is to maintain a high index of clinical suspicion, followed by an accurate clinical scoring assessment using the 4Ts. Next, appropriate stepwise laboratory testing must be undertaken in order to rule out HIT or establish the diagnosis. In the interim, all heparin must be stopped immediately, and the patient administered alternative anticoagulation. Here we review alternative anticoagulation choice, therapy alternatives in the difficult-to-manage patient with HIT, and the problem of overdiagnosis.

Thrombocytopenia After Cardiopulmonary Bypass Is Associated With Increased Morbidity and Mortality

BACKGROUND

Thrombocytopenia is a risk factor for morbidity and mortality in critically ill patients, and is common after cardiopulmonary bypass (CPB). In this study, we evaluate whether thrombocytopenia after CPB is an independent risk factor for postoperative morbidity and mortality.

METHODS

We retrospectively evaluated 1364 patients requiring CPB at the University of Colorado Hospital between January 2011 and May 2016. Platelet nadir, absolute change in platelets, and percent change in platelets were modeled as continuous variables. Patients with postoperative thrombocytopenia (defined a nadir <75 × 10³/μL within 72 hours) were also compared with patients without thrombocytopenia in a propensity-matched model. The primary outcome was in-hospital mortality, and secondary outcomes included postoperative infection, postoperative acute kidney injury (AKI), postoperative stroke, and prolonged intensive care unit (ICU) and hospital lengths of stay (LOS).

RESULTS

Postoperative thrombocytopenia occurred in 356 (26.0%) patients. In multivariable analysis, platelet nadir was significantly inversely associated with mortality (odds ratio [OR], 0.955; 95% confidence interval [CI], 0.934-0.975; P < .001), postoperative infection (OR, 0.992; 95% CI, 0.986-0.999; P = .03), AKI (all stage) (OR, 0.993; 95% CI, 0.988-0.998; P = .01), AKI (stage 3) (OR, 0.966; 95% CI, 0.951-0.982; P < .001), postoperative stroke (OR, 0.974; 95% CI, 0.956-0.992; P = .006), prolonged ICU stay (OR, 0.986; 95% CI, 0.981-0.991; P < .001), and hospital LOS (OR, 0.998; 95% CI, 0.997-0.999; P = .001). Percent change in platelets from baseline was also significantly associated with all primary and secondary outcomes.

CONCLUSIONS

Postoperative thrombocytopenia is independently associated with postoperative mortality, AKI, infection, stroke, and prolonged ICU and hospital LOS. Serial platelet monitoring may help identify patients at higher risk of postoperative complications. Further studies investigating strategies to reduce postoperative thrombocytopenia, including reducing CPB time, are needed.

Antithrombotic therapy management of adult and pediatric cardiac surgery patients

Despite the development of catheter-based interventions for ischemic and valvular heart disease, hundreds of thousands of people undergo open heart surgery annually for coronary artery bypass graft (CABG), valve replacement or cardiac assist device implantation. Cardiac surgery patients are unique because therapeutic anticoagulation is required during cardiopulmonary bypass. Developmental hemostasis and altered drug metabolism affect management in children. This narrative review summarizes the current evidence-based and consensus guidelines regarding perioperative, intraoperative and postoperative antithrombotic therapy in patients undergoing cardiac surgery. Anticoagulation preoperatively is required in the setting of cardiac arrhythmias, prior valve replacement or history of venous thromboembolism. In patients with ischemic heart disease, aspirin is continued in the perioperative period, whereas oral P2Y12 antagonists are withheld for 5-7 days to reduce the risk of perioperative bleeding. Intraoperative management of cardiopulmonary bypass in adults and children includes anticoagulation with unfractionated heparin. Variability in dose-response to heparin and influence of other medical conditions on dosing and reversal of heparin make intraoperative anticoagulation challenging. Vitamin K antagonist therapy is the standard anticoagulant after mechanical heart valve or left ventricular assist device (LVAD) implantation. Longer duration of dual antiplatelet therapy is recommended after CABG if patients undergo surgery because of acute coronary syndrome. Antiplatelet therapy after LVAD implantation includes aspirin, dipyridamole and/or clopidogrel in children and aspirin in adults. A coordinated approach between hematology, cardiology, anesthesiology, critical care and cardiothoracic surgery can assist to balance the risk of thrombosis and bleeding in patients undergoing cardiac surgery.