Physiological Characterization of the SynCardia Total Artificial Heart in a Mock Circulation System

Abstract

The SynCardia total artificial heart (TAH) has emerged as an effective, life-saving bi-ventricular replacement system for a wide variety of patients with end-stage heart failure. While the clinical performance of the TAH is established, modern physiologic characterization, in terms of elastance behavior and pressure-volume characterization has not been defined. Herein we examine the TAH in terms of elastance using a non-ejecting left-ventricle, and then characterize the pressure-volume relationship of the TAH by varying preload and afterload parameters using a Donovan Mock Circulatory System. We demonstrate that the TAH does not operate with time-varying elastance, differing from the human heart. Further, we show that the TAH has a pressure-volume relationship behavior that also differs from that of the human heart. The TAH does exhibit Starling-like behavior, with output increasing via preload dependent mechanisms, without reliance on an alteration of inotropic state within the operating window of the TAH. Within our testing range, the TAH is insensitive to variations in afterload, however this insensitivity has a limit, the limit being the maximum driving pressure of the pneumatic driver. Understanding the physiology of the TAH affords insight into the functional parameters that govern artificial heart behavior providing perspective on differences compared to the human heart.

A Physical Heart Failure Simulation System Utilizing the Total Artificial Heart and Modified Donovan Mock Circulation

“…A Starling Curve for the variations in preload is presented in Fig. , comparing normal left ventricular drive conditions to the reduced drive conditions . Under normal drive conditions a higher EDV was achieved when the right ventricular vacuum was set at −20 mm Hg, reaching an EDV of 84 mL for normal conditions compared to 73 mL at heart failure conditions.…”

“…There are clear variations in the shape of PV loops in the TAH compared with PV loops of the human heart . Under normal operating conditions, the TAH has been shown to be afterload insensitive . However, with the TAH operating in reduced drive heart failure mode, the left ventricle is not always capable of overcoming the afterload and fully ejecting all volume that enters the ventricle during diastole.…”

“…Recently we have defined and characterized a full circulatory mock circulation system consisting of the SynCardia TAH in combination with a modified Donovan Mock Circulation System (DMCS) . This system is robust, capable of physically reproducing a wide range of hemodynamic parameters, for example, pressure and load extremes, is relatively transportable, and is presently installed in many clinical TAH implanting sites as part of the regulatory‐defined training program .…”

Control of the Fluid Viscosity in a Mock Circulation

“…A so‐called mock circulation (MC) allows the in vitro investigation, development, and testing of VADs. Instead of blood, the majority of mock circulations use an aqueous‐glycerol solution to mimic the viscosity of blood in the human body.…”

“…Figure shows the varying viscosity of the working fluids used in several state‐of‐the‐art MCs that have been published within the last 7 years using an aqueous‐glycerol solution with specified values of mixture ratio or viscosity . When only the mixture ratio was specified, we used Cheng's equation to calculate the viscosity assuming a room temperature of 25°C and a mixture ratio being given in mass percentage.…”