Cardiac assist systems

Introduction

Besides of cancer cardiovascular diseases are the main cause of death in modern industrial societies. In a typical European industrial country 5,000 out of a million inhabitants die annually of heart related problems. 2,000 of these patients die immediately without possibility of medical intervention. 500 out of this group are eligible for a cardiac assist. According to estimates of cardiac surgeons 20 % out of these would need a chronic support of the failing heart. There is one method available today to fulfil this need: cardiac transplantation. However, its application has severe limitations, because only a comparably small number of donor hearts is available. It is very unlikely that this number will increase. An example may illustrate this: in 1995 in Germany — 80 million inhabitants — the number of heart transplantations was only about 450. According to the estimates above about 8,000 patients were left without adequate treatment.

The problem of the scarcity of donor hearts cannot be solved with the available medical technology. Only the development of a chronic mechanical cardiac assist system can solve this problem.

The mechanical cardiac assist systems, which are clinically applied today can be divided into three groups:

• centrifugal blood pumps for very short time use,
• pneumatically driven systems for short and intermediate time of use,
• electrically driven systems for an intermediate time of use.

Heart assist systems are usually needed only for the left heart, because it has to supply the whole body with a high blood pressure. These systems are called left ventricular assist devices (LVAD's). They take fluid from the left ventricle and pump it into the aorta.

The Biofluid Mechanics Lab has developed two different heart assist systems:

• an implantable heart assist system
• a partially implantable pneumatic heart assist system

Both systems are described below.

The figure shows a principle sketch of the implantable artificial heart system.

Figure 1: Artificial heart

Here some more information about the energy converter:

An energy converting system that can function for years without maintenance is required for the drive of a LVAD. To meet the requirements of safety, the energy converter should have a simple design with few moving elements. The design applied herein has only one moving part and thus has greater inherent safety than competing systems. The only moving part is the rotor unit, comprised of the impeller of a centrifugal pump, the rotor of an electric motor, and the rotor of an electric axial actuator. A reversal of flow of the transmitter fluid can be achieved with an axial shift of this rotor unit. This fluid acts on the outer surface of a blood chamber and enables it to draw in blood and to expel it. Valves direct the flow of blood. The energy converter performs a flow of 12 L/min at a motor speed of 6,000 rpm against a pressure head of 115 mmHg according to an output of the pulsatile blood pump of 5 L/min.

The energy converter is covered by patents (EU patent no.: 912 50 163; US patent no.: 5 980 568), that are not owned by the lab anymore.

Photo of the device and German article

The pneumatic heart assist system consists of an implantable part, the ventricle, and an extra corporal part, the driver. The figure shows the implantable part of the heart assist system.

Figure 2: Artificial heart