The Changing Landscape of Heart Disease

Medical science has made major inroads in the treatment of Heart Disease. Patients with heart disease who in earlier years would not have survived are alive because of newer drugs, stents or heart surgery. These patients frequently have sustained damage to their heart from previous heart attack, cardiomyopathy or other cause, and they go on to develop heart failure.

The National Heart, Lung and Blood Institute, a branch of The National Institute of Health, reports that the present pool of Heart Failure patients in the U.S. is over 5,000,000 people. There are 550,000 new cases added to this pool each year and Heart Failure is the leading cause of hospital admission for patients over 65 with an annual cost of over $32 billion. The incidence of heart failure is increasing and this trend is expected to continue as the population ages and as treatment improves for other types of heart disease. Early heart failure responds to medication but end stage disease requires heart transplant or some type of mechanical assistance pump.

Mechanical Ventricular Assist Devices

The shortage of available donor hearts limits heart transplants. Mechanical blood pumps have become a viable alternative. These pumps are often referred to as ventricular assist devices. In some cases these mechanical pumps function as a bridge. They support the heart until a donor heart for transplant is available or until the patient’s own heart heals. In other cases the mechanical pump will support the patient indefinitely. Mechanical blood pumps are also used for short-term support of the circulation during heart surgery. Blood pumps for this purpose have been available for years but a more physiologic blood pump such as we are proposing here would be an improvement.

The first generation of these devices was ventricle type pumps. Although they provided pulsatile flow, in contrast to the natural heart the parameters of flow through the device such as shear and Reynolds number were dependent on the fixed geometry of the outer shell of the device. The size and durability of these early pulsatile devices as well as associated thromboembolism and infection were issues that needed improvement. To overcome these issues, new approaches were explored using continuous flow pumps. Continuous flow pumps are very small turbines or centrifugal pumps that spin at thousands of revolutions per minute similar to small pumps used in industrial applications. Because of their small size and simplicity, these continuous flow pumps have, to a great degree, replaced the older pulsatile devices in clinical practice.

As more experience is obtained with these continuous flow devices, major problems are becoming apparent. Stroke, thrombosis and non-surgical bleeding are issues as well as infection. High non-physiologic levels of fluid shear related to the high-speed impeller cause or contribute to these problems. Because the high-speed impeller is the critical part of the device, it is difficult to eliminate this issue with this type of device. In addition these devices provide non-pulsatile flow. Although non-pulsatile flow is tolerated, the problems associated with long term non-pulsatile flow are gradually becoming apparent.

Blood flow parameters in the heart, particularly fluid shear are very important. Platelets, some types of blood cells and the von Willibrand molecule are known to be sensitive to fluid shear. It is essential to control these parameters of blood flow through the heart to control thromboembolism, bleeding and infection. There are a number of things important in this regard but fluid shear and other parameters of flow are high on the list.

The Innovation

The ElishaHeart* innovation brings an entirely new design concept to pulsatile ventricular assist devices. An expansile (elastic) pumping bladder is used. This is in contrast to the flexible, but not elastic, pumping bladder or diaphragm used in first generation pulsatile devices. This expansile pumping bladder emulates the action and function of the walls of the natural heart. The walls of the pumping bladder are stretched by drawing a vacuum on the driving side of the bladder during the filling phase (diastole). Elastic energy is stored in the walls of the bladder and this energy is then used to pump, or help pump, the blood as the bladder wall recoils to its resting position during the ejection phase (systole). This action provides a method for modeling the flow of blood through the device. By making various areas of the walls of the pumping bladder out of polymer material with different viscoelasticity and different thickness, some areas of the walls of the pumping bladder can be designed to stretch earlier than others and some areas can be designed to recoil earlier than others.

In the natural heart, all the muscle segments in the walls of the ventricle do not contract simultaneously. Various segments contract earlier than others. As these various segments contract in sequential fashion, they direct the blood flow through the heart maintaining parameters of blood flow through the heart in physiologic range. With appropriate design, the various segments of this elastic pumping bladder will also contract sequentially and will direct the blood through the pumping bladder similar to the way the muscular walls of the heart direct the blood through the natural heart. Shear, Reynolds number and other parameters of flow will be maintained in physiologic range. The thrombosis, bleeding, infection and other problems that are due to nonphysiologic parameters of flow will be controlled as the parameters of flow will be maintained in physiologic range.

Advancing this concept to practice requires formulating a series of polymers, each with a slightly different viscoelasticity and all with minimal hysteresis and creep and adequate durability. The mathematical analysis to determine the local viscoelasticity and motion of the various segments of the pumping bladder to achieve physiologic flow parameters through the pumping bladder is complex. We have identified and consulted with experts in mathematics and polymer chemistry who have extensive experience with biological systems, particularly the heart. They estimate this can be done by modifications of available polymers and the application of available mathematical techniques.

The first phase in building the prototype is formulating and testing the series of polymers based on the requirements of the initial mathematical design. This is an iterative process as the mathematical design is constrained by the possible polymer formulations. After the series of polymers is formulated the next phase will be fabrication and testing of the pumping bladder.

A pulsatile device emulating the function of the natural heart would be ideal provided it could overcome the problems associated with earlier pulsatile devices. Such a device would maintain the hemodynamic parameters of the system in physiologic range so that with regard to hemodynamics, neither the blood being pumped nor the peripheral vascular system would see this device as anything other than a natural heart. The ElishaHeart innovation of an elastic pumping bladder in which various segments of the bladder wall contract sequentially provides a method to build such a device.

THE THERAPEUTIC APPLICATION

This innovation represents a new generation in the evolution of pulsatile ventricular assist devices (VADs). The walls of the pumping bladder actively model blood flow through the device similar to the way blood flow is modeled in the natural heart. Industry sources estimate the current worldwide demand for VADs at over $2 billion this year and it is expected to grow to between $7.5 billion and $12 billion annually in five years. A significant innovation in the design of VADs and artificial hearts, like the ElishaHeart technology, will determine how rapidly the market reaches its potential.

Dr. Arthur S. Palmer, a cardiothoracic surgeon and a mechanical engineer, created the breakthrough technology. The ElishaHeart technology has three patents issued in the United States and one in Europe. It is anticipated that additional patents will be filed and issued as development proceeds.

Dr. Palmer has assembled a team of world leaders in multiple disciplines including mathematics, polymer science and engineering to create this truly innovative cardiac assist device. These collaborators are confident that the project is valuable and has a high likelihood of success.

For further information, contact Art Tauder at Thunderhouse LLC art@thunderhouse.org or by phone at 203-451-2699.

* The name "ElishaHeart" was derived from a Biblical story of resuscitation -- breathing new life -- from Kings II: Chapter 4.