Abstract
Around 1% of the UK population suffer from heart failure. While many are treated using the available drugs, for some the only solution is a heart transplant. However, only around 120 transplants are performed in the UK each year and many patients die while waiting for a heart. Mechanical circulatory support devices have been developed to assist the circulation until a suitable donor can be found. Ventricular assist devices (VADs) are pumps which work in parallel with the native heart to augment the function of one or both of the ventricles. Compared with optimal drugs VADs double the one year survival rate and significantly increase quality of life. It has also been shown that in specific patient populations, VADs, in combination with drugs, can reverse end stage heart failure. However there are still a number of problems. Modern VADs are small axial or centrifugal rotary pumps which supply a continuous flow of blood to the arteries. There are high shear stresses on the blood which lead to blood trauma including hemolysis, platelet activation, emboli and destruction of von Willebrand factor. In addition the steady flow has the potential to cause changes in the blood vessels. Computational fluid dynamics studies of haemodynamics in a range of VADs were used to show how the geometry and operation of a device effect shear stresses and residence times. A numerical model for haemolysis was developed and validated against in vitro measurements and can be used to compare device prototypes. The most common complication with VADs is bleeding. Future work will involve assessment of the effects of destruction of von Willebrand factor, and reduced arterial pulse, on gastrointestinal bleeding, using numerical, in vitro and in vivo models. If the current problems with VAD technology can be eliminated more patients can be supported, and may recover from heart failure.