An Intraventricular Soft Robotic Pulsatile Assist Device for Right Ventricular Heart Failure1

摘要

Heart failure occurs when either or both ventricles of the heart cannot pump sufficient blood to meet the metabolic needs of the body. While symptoms vary widely depending on which ventricle is failing and the underlying cause, the standard indicator of failure is low ejection fraction, which is the volumetric proportion of blood ejected when the ventricle contracts. Effective therapies for heart failure target the etiology, but treatment of symptoms is also necessary to sustain patient health and quality of life. Though early-stage heart failure can be treated with drugs, more advanced cases require support from a ventricular assist device (VAD) [1]. Such devices assume some or all of the heart's pumping work, unloading the heart and restoring normal circulation, until the patient recovers or a transplant becomes available.Due to its more complex geometry and motion, right ventricular heart failure (RVHF) is less understood than left ventricular heart failure and has fewer treatment options. Currently, only 1 implantable and 2 paracorporeal devices are FDA-approved for mechanical circulatory support of the right ventricle [2], and all are originally left ventricular assist devices set to produce lower pressures. Implantation requires cannulation via sternotomy, which is a very invasive procedure. In addition, all current VADs require blood to flow through the device, which presents a thrombogenic risk. Newer VADs mitigate this by using magnetic suspension for contactless bearings, but this is power-intensive and reduces portability. This paper presents the design of a VAD tailored for the right ventricle, which leverages its specific geometry and lower pressure in order to avoid the major pitfalls of current VADs.From clinician input, it was determined that the device must be compact enough to span the right ventricle and be deliverable via a minithoracotomy procedure. In addition, to reduce the need for a strong anticoagulation regimen, which has undesirable side-effects, we sought to minimize the surface area of contact between the device and the blood. Because the target population is adolescents, many with congenital heart defects, the device also needed to be compatible with anatomical variation. Finally, we determined that the device should be able to generate the physiological 30 mmHg of systolic pressure in the right ventricle, which translates to an estimated 7 N of force applied on the walls.The final device concept employs the use of a soft robotic linear actuator anchored in the free wall of the right ventricle and the septum (Fig. 1). The actuator contracts and brings the walls of the right ventricle together, contributing to the ejection of blood from the ventricle into the pulmonary artery.The actuator is a pneumatic artificial muscle consisting of an inflatable inner bladder constrained by a braided mesh, which contracts in length when pressurized. To avoid the risk of air embolisms, the final device will use hydraulics instead of pneumatics. The actuator is only 5 mm in diameter when unpressurized, facilitating minimally invasive delivery. It is also very soft, with the inner bladder molded out of a 30 Shore OO hardness silicone rubber. This allows for operation at low pressures below 15 psi, and safer direct tissue contact.Two anchors hold the device in place, one on the septal wall and one on the right ventricular free wall (RVFW). The septal anchor is delivered through the septum and unfolds in the left ventricle (Fig. 2), and was thus designed to prioritize deliverability. The final design is a 1 mm thin circular disk made of Elastosil (Wacker), a 28 Shore A hardness silicone rubber, and provides sufficient resistance to device pullout while still fitting inside a 10 mm-diameter delivery tube.The free wall anchor design prioritizes adjustability and tight sealing to prevent blood leakage (Fig. 3). A thin Elastosil disk is deployed against the inner surface of the RVFW to provide a seal against leaks, and