Related Experiment Video
Updated: May 26, 2026
In Vitro Thrombosis Test for Ventricular Assist Devices
Published on: March 21, 2025
Chronic in vivo testing of the Penn State infant ventricular assist device
William J Weiss1, Elizabeth L Carney, J Brian Clark
1Department of Surgery, Penn State College of Medicine, Hershey, Pennsylvania, USA. bweiss@psu.edu
Insights
The Penn State Infant Ventricular Assist Device (VAD) achieved 4-6 weeks survival in juvenile sheep. Optimized anticoagulation protocols minimized heparin use and prevented thromboembolism, showing promising results for pediatric circulatory support.
Area of Science:
- Biomedical Engineering
- Cardiovascular Research
- Pediatric Medical Devices
Background:
- Pediatric circulatory support remains a critical challenge.
- Existing ventricular assist devices (VADs) require significant anticoagulation.
- The Penn State Infant VAD was developed to address these limitations.
Purpose of the Study:
- To evaluate the chronic performance and safety of the Penn State Infant VAD in a juvenile ovine model.
- To compare two anticoagulation protocols for VAD support.
- To assess the incidence of thromboembolism and device-related thrombi.
Main Methods:
- Seven chronic animal studies were conducted using juvenile sheep (mean weight 23.5 ± 4.1 kg).
- Animals received VAD support with either a target activated partial thromboplastin time (aPTT) or a target thromboelastography R-time.
- Unfractionated heparin was used for anticoagulation, with monitoring of heparin activity (anti-Xa).
Main Results:
- Five of seven studies achieved the 4-6 week survival goal, with a mean support duration of 26.1 days.
- The thromboelastography-guided anticoagulation protocol required significantly less heparin and showed minimal heparin activity.
- No significant thromboembolism was observed, except in one animal with infection; device thrombi were minimal and reduced with custom valves.
Conclusions:
- The Penn State Infant VAD demonstrates encouraging chronic performance in a juvenile ovine model.
- Optimized anticoagulation strategies, particularly thromboelastography-guided, can reduce heparin requirements while maintaining safety.
- These findings support the potential of the Infant VAD for pediatric circulatory support.
Abstract:
The Penn State Infant Ventricular Assist Device (VAD) is a 12-14 ml stroke volume pneumatically actuated pump, with custom Björk-Shiley monostrut valves, developed under the National Heart, Lung, and Blood Institute Pediatric Circulatory Support program. In this report, we describe the seven most recent chronic animal studies of the Infant VAD in the juvenile ovine model, with a mean body weight of 23.5 ± 4.1 kg. The goal of 4-6 weeks survival was achieved in five of seven studies, with support duration ranging from 5 to 41 days; mean 26.1 days. Anticoagulation was accomplished using unfractionated heparin, and study animals were divided into two protocol groups: the first based on a target activated partial thromboplastin time of 1.5-2 times normal, and a second group using a target thromboelastography R-time of two times normal. The second group required significantly less heparin, which was verified by barely detectable heparin activity (anti-Xa). In both groups, there was no evidence of thromboembolism except in one animal with a chronic infection and fever. Device thrombi were minimal and were further reduced by introduction of the custom valve. These results are consistent with results of adult VAD testing in animals and are encouraging given the extremely low levels of anticoagulation in the second group.
