Author: Melissa Colizza, MD - Centre Hospitalier Universitaire Sainte-Justine - Montreal, Quebec
A seven-year-old, 23 kg male has a left ventricular-assist device (LVAD) due to dilated cardiomyopathy. Which of the following devices is associated with the HIGHEST risk of thromboembolic complications?
Heart failure affects 0.7-7.4 children per 10,000 globally. The mortality rate is 7-15% in patients with severe heart failure in the United States. Although heart transplantation is a definitive treatment, the number of patients on the heart transplant waiting list exceeds the number of donor hearts available. Thus, mechanical support with extracorporeal membrane oxygenation (ECMO) or ventricular assist devices (VADs) has been utilized as a bridge-to-recovery, bridge-to-transplant, or destination therapy. VAD placement prior to the onset of end-organ dysfunction reduces waitlist mortality, but there are still significant complications associated with VADs. Appropriate VAD selection in the pediatric population remains challenging. Patient size (body surface area) and anticipated duration of support are the primary considerations when choosing a particular device. The ideal device would account for the physiologic differences in pediatric versus adult patients with minimal risk of hemolysis or thromboembolism.
The Berlin Heart EXCOR (BHE), a paracorporal pulsatile flow device, has been used in the pediatric population since the 1990s and is the only FDA-approved VAD for children with a body surface area (BSA) less than 0.6 m2. The volume capacity of the BHE pneumatic pump and set heart rate determine cardiac output. The BHE has been used successfully as a bridge to recovery and bridge to transplantation in children. However, BHE implantation is associated with a higher rate of thrombosis and adverse neurological events compared to the continuous-flow devices. A 2018 literature review (including 27 studies) analyzing antithrombotic therapies and thromboembolic complications in 558 children with different types of VADs (87% BHE and 1.8% Heartware HVAD) by Huang et al reported an overall incidence of thromboembolic events in 26% of patients. The overall incidence of thromboembolic complications ranged from 22 to 56% in patients with the BHE the studies included.
Conversely, there is a lower rate of thromboembolic events with continuous-flow devices. Rates of thromboembolic events in patient cohorts with the Heartmate II (HM2) in the early 2010s were reported at less than 15%. The newer generation, Heartmate III (HM3), is another continuous-flow device with magnetically levitated bearings and intrinsic pulsatility, allowing ejection through the aortic valve thereby decreasing the shear stress and compressive forces on blood which is known to lead to thrombosis. It has been the only FDA-approved long-term continuous-flow device for children since the recall of the Heartware (HVAD) in 2021. A 2020 study by O'Connor and colleagues investigated outcomes in 35 pediatric and adult congenital cardiac patients who had undergone HM3 implantation. They reported no episodes of pump thrombosis, pump dysfunction requiring exchange, or stroke. While the recommended patient body surface area for HM3 implantation is greater than 1.4 m2, successful implantation has been reported in a patient with a BSA of 0.78 m2. A 2022 meta-analysis by George and colleagues (using twelve papers) investigated the complications associated with different types of VADs placed in infants and children. The study demonstrated that the BHE was associated with the highest risk of thromboembolic complications compared with the HVAD and HM3 (continuous flow devices). The authors postulate that this increased risk may be related to the more complex design of pulsatile VADs, such as one-way valves, which create areas of stagnant flow. In contrast, with continuous-flow devices, thrombosis may be caused by increased shear stress and heat generated by the pump. Although the HeartWare HVAD was commonly used in older children, it was withdrawn from the markets in 2021 due to an increased risk of neurological complications and technical failure related to the battery.
The HM3 seems to be the most promising mechanical support device with respect to safety and freedom from thromboembolic events. However, the BHE remains the only FDA approved device that is available on the market for neonates, whom are intrinsically at a higher risk for both thromboembolic and hemorrhagic complications. Notably, it is important to remember that anticoagulation protocols vary between individual patients, devices, and institutions.
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