Paving the way for destination therapy of end-stage biventricular heart failure: the ReinHeart total artificial heart concept.

Abstract

The rising demand for cardiac transplantation and the steady decline in the number of instances of organ donation pose a serious challenge to physicians dealing with biventricular end-stage heart failure. Total artificial heart (TAH) therapy is therefore an alternative of growing importance. Three systems are currently available: The SynCardia-TAH (SynCardia Systems, Inc., Tucson, AZ, USA), the AbioCor-TAH (Abiomed, Inc., Danvers, MA, USA) and since recently the CARMAT-TAH (Carmat SA, Velizy Villacoublay, France). The ‘SynCardia’ is the only TAH system widely available. In addition to being a bridge to transplant [1, 2], the US Food and Drug Administration (FDA) recently approved a Humanitarian Use Device designation for the SynCardia-TAH for its use for destination therapy (DT) in patients not eligible for transplantation [3]. The limitations of this technology are mechanical parts that are prone to wear and tear, the need for percutaneous tubes and dependence on a permanent external driver. The ‘AbioCor-TAH’ was the first totally implantable, electrically driven TAH, designed as an alternative to cardiac transplantation. Although approved under the Humanitarian Device Exemption program in 2006, the device is currently not implanted due to its limited clinical success [4]. Finally, the ‘CARMAT’ is a fully implantable, electrohydraulically driven, pulsatile flow device with four bioprosthetic valves. Its artificial ventricles consist of processed bioprosthetic pericardial tissue and expanded polytetrafluorethylene [5]. The first-in-man implant was performed in 2013. The duration of support was 74 days. The feasibility trial is still ongoing. Durability and maintenance-free operation are essential requirements incorporated into any TAH design to facilitate long-term support. Reliable operation and broad applicability depend on small dimensions of the pump unit, low weight, low thermal losses, minimal haemolysis and thrombogenicity, sufficient pumping capacity and redundancy in all possible system components. These requirements are addressed by the ‘ReinHeart’ (Fig. 1). This is an electrically driven TAH currently being developed on this basis by our institutions. It is designed as an alternative to heart transplantation and aimed to support patients for at least 5 years. The size of the pump unit and the orientation of the inand outlets have been optimized according to anatomical and virtual fit studies [6]. A first major characteristic of the ReinHeart concept is the application of a linear motor concept that diminishes the need for wearprone components such as ball-bearings, gears and lubricants, increasing the durability and reliability of the pump unit. The linear motor is directly connected to a left and a right pusher plate, guided by a single linear bearing. The pusher plates are actuated in an alternating way, pumping the blood out of the chambers in a physiological sinusoidal pattern. The chambers consist of highly biocompatible transparent methacrylate–acrylonitrile–butadiene– styrene thermoplastic copolymer. Four mechanical valves (St Jude Medical, Inc.; St Paul, MN, USA) facilitate unidirectional blood flow. A second major characteristic of the ReinHeart is that the pump chambers are not mechanically attached to the pusher plates, enabling a preload sensitive filling and consequently ejection of the ventricles. This allows a robust implementation of a starling-like behaviour similar to the natural heart. In contrast to the AbioCor and the CARMAT-TAHs, vulnerable pressure sensors are not required for this purpose. Depending on operational frequency and preload, the artificial ventricles can generate a pump flow of up to 7.5 l/min. Figure 2 gives an overview of the system components. The implanted components are the pump unit, an implantable controller, a transcutaneous energy transmission (TET) system and a compliance chamber that optimizes ventricular filling. External patient equipment consists of the primary TET coil and a user interface with batteries. The TET system supports the device up to a distance of 30 mm. The batteries are charged by connecting the outer coil of the TET system and can operate the device for 45 min at full capacity. Total implantability of the system components facilitates increased patient mobility and silent operation, thus contributing to a significantly increased quality of life.