Heparin-Induced Thrombocytopenia Complicating Support by the Berlin Heart

Hemostasis in Pediatric Extracorporeal Life Support: Overview and Challenges

Extracorporeal membrane oxygenation (ECMO) and ventricular assist devices (VADs) are increasingly used in critically ill children. Despite improvements in mechanical design and clinical management, thromboembolic and hemorrhagic events remain significant causes of morbidity and mortality related to the use of both devices. Choice of anticoagulant agents and assays for monitoring continue to present challenges in management. In this review, we describe the incidence and risk factors for thrombosis and hemorrhage, the different types of anticoagulants currently in use, the assays available for monitoring anticoagulation, and management of thromboembolic and bleeding complications in children on mechanical circulatory support (MCS). We conclude by emphasizing the areas that need further study to minimize the risk for thrombosis and hemorrhage in the use of ECMO and VAD in children.

The blood compatibility challenge. Part 4: Surface modification for hemocompatible materials: Passive and active approaches to guide blood-material interactions

Biomedical devices in the blood flow disturb the fine-tuned balance of pro- and anti-coagulant factors in blood and vessel wall. Numerous technologies have been suggested to reduce coagulant and inflammatory responses of the body towards the device material, ranging from camouflage effects to permanent activity and further to a responsive interaction with the host systems. However, not all types of modification are suitable for all types of medical products. This review has a focus on application-oriented considerations of hemocompatible surface fittings. Thus, passive versus bioactive modifications are discussed along with the control of protein adsorption, stability of the immobilization, and the type of bioactive substance, biological or synthetic. Further considerations are related to the target system, whether enzymes or cells should be addressed in arterial or venous system, or whether the blood vessel wall is addressed. Recent developments like feedback controlled or self-renewing systems for drug release or addressing cellular regulation pathways of blood platelets and endothelial cells are paradigms for a generation of blood contacting devices, which are hemocompatible by cooperation with the host system. STATEMENT OF SIGNIFICANCE: This paper is part 4 of a series of 4 reviews discussing the problem of biomaterial associated thrombogenicity. The objective was to highlight features of broad agreement and provide commentary on those aspects of the problem that were subject to dispute. We hope that future investigators will update these reviews as new scholarship resolves the uncertainties of today.

Heparin-induced thrombocytopenia in patients with ventricular assist devices: are new prevention strategies required?

Heparin-induced thrombocytopenia (HIT) is caused by platelet-activating antiplatelet factor 4/heparin antibodies. However, clinical HIT (thrombocytopenia or thrombosis, or both) develops in only a minority of patients who form antibodies. It is difficult to distinguish HIT from non-HIT thrombocytopenia in patients after ventricular assist device (VAD) implantation. Further, the risks of heparin-induced immunization and clinical HIT approach 65% and 10%, respectively, in this patient population, with a particularly high risk of cerebrovascular ischemia/infarction. Given the apparent high risk of HIT and its complications, and the diagnostic challenges, we suggest that the VAD patient population be evaluated using alternative, nonheparin agents for routine postimplantation anticoagulation.

Prevalence of heparin-dependent platelet antibodies in children after cardiopulmonary bypass

OBJECTIVE

To determine the prevalence of heparin-dependent platelet antibodies (HDPA) in children requiring heparin for >5 days after cardiopulmonary bypass surgery.

DESIGN

Prospective, observational study.

SETTING

Tertiary care pediatric intensive care unit.

PATIENTS

Thirty children were enrolled: 15 patients <30 days old and 15 patients between 30 days and 12 yrs of age.

INTERVENTIONS

Detection of HDPA by heparin-platelet factor 4 enzyme-linked immunosorbent assay after 5-10 days of postoperative heparin exposure. Positive or equivocal results were confirmed with serotonin release assay.

MEASUREMENTS AND MAIN RESULTS

There were no confirmed cases of HDPA in this study (95% confidence interval 0-11.6%). Despite the lack of HDPA, the study population was at high risk of thrombosis with symptomatic clot developing in six patients (20%). Clinical models developed in adults to determine the pretest risk of heparin-induced thrombocytopenia were not valid in this study population.

CONCLUSIONS

The prevalence of HDPA in children after cardiopulmonary bypass surgery is low. After bypass surgery, critically ill children are at risk of developing thrombosis from multiple etiologies, and suspicion of heparin-induced thrombocytopenia needs to be confirmed with laboratory testing including a functional assay.

Successful treatment of ventricular assist device associated ventricular thrombus with systemic tenecteplase

We report a case of intracardiac thrombus in a patient supported by the Jarvik 2000 Flowmaker successfully treated with a single dose of peripherally administered TNK-tissue plasminogen activator (Tenecteplase, Metalyse, Boehringer Ingelheim). This strategy may be considered in the case of life-threatening VAD associated thrombosis to avoid the need for intracardiac drug delivery or VAD replacement. We also discuss the apparent increased thrombotic risk in patients receiving a VAD for chemotherapy induced cardiomyopathy and the implications this may have for the choice of VAD.