Devices that provide support on a more long-term basis are also available. The Syncardia total artificial heart is a pulsatile system that replaces both heart ventricles with mechanical pumps, with the ventricles pneumatically driven through an external driver. The EXCOR VAD is an extracorporeal pneumatically driven pulsatile pump that uses silicone cannulas to connect to the atrium or ventricle and to the great arteries. Because the device is not completely implantable and requires a large driver, children receiving EXCOR support must remain hospitalized.
The HeartMate II (Abbott) is an intracorporeal continuous flow axial device that can fully support left ventricular function in patients who weigh more than 30 kg; it operates with a pump implanted in an intraperitoneal pocket, an inflow cannula in the left ventricle, and an outflow cannula in the ascending aorta.
A fourth device is the Jarvik 2015, another intracorporeal axial pump that has received regulatory approval for pediatric clinical trials. It is a redesign of a previous version that resulted in unacceptable levels of hemolysis. Experimental studies show that the newer version does not appear to have the same problem.
Hematologic Challenges in MCS
The authors noted that MCS devices cause multiple changes in the hematologic system because of the biomaterials used and the “shear forces” they create. When blood comes into contact with biomaterials, both the complement and contact pathways are activated and inflammatory cytokines are produced. The amount of platelet activation caused by MCS is currently unclear, as it depends on what methodology is used for identifying activation.
Perhaps the most devastating and potentially fatal adverse events related to MCS are stroke and pump thrombosis, which can occur in up to 30% of patients. Because of the high incidence of thrombosis, antithrombotic therapy is used in all MCS devices as a preventive measure. Studies have evaluated the safety and efficacy of some antithrombotic therapy regimens for patients supported by MCS, but the regimen of choice varies depending on the type of MCS device being used and on the individual treatment center. One survey examining antithrombotic therapy practices for patients supported by ECMO in centers belonging to the Extracorporeal Life Support Organization found that 100% of centers used unfractionated heparin at varying infusion rates. However, at the time of the survey, only 8% of centers were using direct thrombin inhibitors (ie, argatroban and bivalirudin) even though approximately half had access to them.
The authors noted the importance of hematologists’ understanding regarding which antithromobotic therapies are used at baseline in order to provide recommendations if hemorrhage or thrombosis occur. In a study of children supported by EXCOR who received antithrombotic therapy, 11% to 43% experienced gastrointestinal bleeding and intracranial hemorrhage, and 9% to 38% experienced ischemic stroke. Further analysis suggested that stroke and bleeding events could be reduced by earlier initiation of aspirin and a faster upward dose titration, steroid use in some cases, and the optimization of hemostasis prior to initiating anticoagulation.
Additional challenges in treating patients on MCS also include the influence of thrombophilia on the risk for thrombosis, as well as management of heparin-induced thrombocytopenia.
“Input from hematologists [on] development of evidence-based antithrombotic strategies has the potential to significantly improve the outcomes for patients treated with MCS,” the authors concluded.
1. Baumann Kreuziger L, Massicotte MP. Adult and pediatric mechanical circulation: a guide for the hematologist [published online November 30, 2018]. Hematology Am Soc Hematol Educ Program. doi: 10.1182/asheducation-2018.1.507