Artificial Heart Valves

The cardiovascular system is a closed circulatory system that ensures blood flow through the human body. Blood circulates through two systems; the first is responsible for pushing blood from the heart to the lungs to capture oxygen, and the second is responsible for distributing oxygenated blood to body organs. This system is composed of a double pump with branched tubes that leads blood from the heart to the organs (arteries) and returns it to the heart (veins). The heart is essentially a muscular pump with four rooms, two for receiving incoming blood (atria) and two for pushing blood toward the organs (ventricles). In order to maintain unidirectional flow of blood, 3-D open-close ‘‘gateways’’ (valves) are optimally located between atria and ventricles, and between the ventricles and the emerging arteries. The workload of heart valves is nothing short of extraordinary. The valves open and close once per second totaling more than 3 billion times in a lifetime. These movements take place under constant pressure and in flowing blood, a very viscous fluid rich in minerals, proteins, lipids, and cells. Valves may progressively become defective and critically influence the performance of the heart. These defects are collectively named valve diseases. As the properties of normal and diseased valves are not sufficiently understood, no drugs are available to treat and cure valve diseases. The only curative solution is to perform open-heart surgery to replace diseased valves with artificially engineered devices. These valve substitutes are nonliving materials fashioned in the form of valves that reestablish initial mechanical functions and restore the functionality of the heart. However, these devices may eventually fail because of imperfections in design, composition, or biocompatibility. Once a device shows signs of failure, the patient requires a second open-heart surgery for replacement of the defective device. Reoperations are generally risky and pose additional problems for children who naturally outgrow their implants. Thus, the long-term goal of biomedical engineering is to find better methods for treating valvular diseases and thus impact lives of millions of patients worldwide. This daunting effort brings together a multidisciplinary team of specialists in medicine, biology, engineering, and mechanics. This chapter describes the structure, function, biology, and pathology of heart valves; information on current replacement devices; and the necessary prerequisites for constructing an ‘‘ideal’’ replacement valve. Ongoing research is aimed at improving existing devices by enhancing biocompatibility, as well as pioneering work on novel tissue-engineering approaches, which would facilitate complete regeneration of valve tissues.