The Syncardia(™) total artificial heart: in vivo, in vitro, and computational modeling studies

Abstract

The SynCardia(™) total artificial heart (TAH) is the only FDA-approved TAH in the world. The SynCardia(™) TAH is a pneumatically driven, pulsatile system capable of flows of >9L/min. The TAH is indicated for use as a bridge to transplantation (BTT) in patients at imminent risk of death from non-reversible bi-ventricular failure. In the Pivotal US approval trial the TAH achieved a BTT rate of >79%. Recently a multi-center, post-market approval study similarly demonstrated a comparable BTT rate. A major milestone was recently achieved for the TAH, with over 1100 TAHs having been implanted to date, with the bulk of implantation occurring at an ever increasing rate in the past few years. The TAH is most commonly utilized to save the lives of patients dying from end-stage bi-ventricular heart failure associated with ischemic or non-ischemic dilated cardiomyopathy. Beyond progressive chronic heart failure, the TAH has demonstrated great efficacy in supporting patients with acute irreversible heart failure associated with massive acute myocardial infarction. In recent years several diverse clinical scenarios have also proven to be well served by the TAH including severe heart failure associated with advanced congenital heart disease. failed or burned-out transplants, infiltrative and restrictive cardiomyopathies and failed ventricular assist devices. Looking to the future a major unmet need remains in providing total heart support for children and small adults. As such, the present TAH design must be scaled to fit the smaller patient, while providing equivalent, if not superior flow characteristics, shear profiles and overall device thrombogenicity. To aid in the development of a new "pediatric," TAH an engineering methodology known as "Device Thrombogenicity Emulation (DTE)", that we have recently developed and described, is being employed. Recently, to further our engineering understanding of the TAH, as steps towards next generation designs we have: (1) assessed of the degree of platelet reactivity induced by the present clinical 70 cc TAH using a closed loop platelet activity state assay, (2) modeled the motion of the TAH pulsatile mobile diaphragm, and (3) performed fluid-structure interactions and assessment of the flow behavior through inflow and outflow regions of the TAH fitted with modern bi-leaflet heart valves. Developing a range of TAH devices will afford biventricular replacement therapy to a wide range of patients, for both short and long-term therapy.

Fig. 1

Three components of the SynCardia^™ TAH system. (a) Representation of a patient implanted with the TAH. Note right and left ventricles, drivelines and an external driver—original “Big Blue” and (b) actual photo of the TAH ventricles with attached outflow grafts and incorporated drivelines.

Fig. 2

Exploded view of SynCardia^™ TAH ventricle. Note housing assembly, diaphragms and base creating separated blood and air chambers.

Fig. 3

(a) Motion of TAH diaphragm assembly and corresponding airflow and pressure waveforms for fill phase and (b) ejection phase.

Fig. 4

Range of pneumatic drivers for the SynCardia^™ TAH. Left—original circulatory support system (CSS) or “Big Blue” driver. Middle—new Companion driver (precursor to Companion 2) and right—Freedom portable “discharge” driver.

Fig. 5

(a) SynCardia^™ TAH left ventricle and a schematic of the flowloop used for the platelet activity measurements and (b) platelet activity rate (PAR) at 6.7 and 8.7 L/min cardiac outputs (p<0.05) (bottom).

Fig. 6

SynCardiaTM with open (green) and closed (red) Medtronic Open Pivot bileaflet mechanical heart valves showing the various rotational valve orientations (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

Fig. 7

Ejection phase of an actual TAH (left) and FSI results (right) showing similar nonuniform deformations of the membrane.

Fig. 8

Velocity magnitude pathlines—shown here for the 55O Medtronic Open Pivot MHV orientation.

Fig. 9

Multiple passages PDF (‘thrombogenic footprint’) for the various valve orientations studied. The “leftward shift” towards lower SA values indicates that the 55° valve orientation (shown in blue) is the optimal orientation for reduced thrombogenicity (majority of the platelets experience lower flow induced stresses) (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)