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Expanding the Pool of Organs for Transplant

Heart transplantation does not adequately address the magnitude and severity of advanced heart failure (HF), a global public health concern that has the potential to reach epidemic proportions. While the gold standard for treating end-stage HF continues to be heart transplantation, there are simply not enough donor hearts available (about 2,000) for the more than 3,000 Americans on the transplant wait list. As such, doctors and scientists are developing alternative means for providing cardiac support, many of which will make an impact in the next decade.

Mechanical circulatory support devices (MCSDs) have the potential to treat many of the patients with end-stage HF, and more than 300,000 American patients each year qualify for some kind of mechanical assist device. These innovative devices replace some of the mechanical functions of the failing heart while improving cardiac output and organ perfusion.

The role of MCSDs in advanced heart replacement therapy is increasing steadily, with some thinking that the improvement in prolonged mechanical circulatory support brought on by their rotary blood pumps could have the potential to overcome heart transplant in the next decade. This would not only provide unrestricted, off-the-shelf solutions in terms of symptomatic relief, but also improve quality of life to those without access to transplantation.

Advances in the technology of MCSDs includes miniaturization, versatility with biventricular support devices, complete internalization, improved hemocompatibility profiles, and responsiveness to cardiac loading conditions. As such, MCSDs could potentially surpass heart transplantation as the primary therapy for advanced heart failure.

Presently, due to the long rehabilitation and potential complications of heart transplant surgery, only about 35 percent of patients with left ventricle assist devices (LVADs) ever get transplanted. Understanding this barrier in moving patients from mechanical support to transplantation, researchers in Chicago recently implanted the first intravascular ventricular assist (iVAC) system to assist and support a patient awaiting a heart transplant. This novel system doesn’t require open-heart surgery, and it reduces pain and dramatically shortens rehabilitation. The bulk of the system is in the six-pound external drive that’s carried over one shoulder.

An increasing number of people are succumbing to heart disease each year because there are too few hearts available for transplantation. To meet this vital need, a group of Boston-based scientists has successfully grown human heart tissue by using messenger RNA to revert skin cells to stem cells that could then be stimulated to grow into cardiac muscle tissue.

While this is a major step toward bioengineering hearts for people in need of a transplant, creating an entire human heart in the lab from a patient’s own genetic material is still some time away. However, this novel research is expected to be used in the coming years to regenerate tissue in hearts damaged by heart attack or heart failure, thereby eliminating their need for a heart transplant in the future.

Another group of Boston researchers is attacking the heart shortage problem by using CRISPR/Cas9 gene editing in an effort to create an endless supply of safe and dependable pig hearts suitable for use in humans. The initial goal of this process, known as xenotransplantation, is to develop implantable porcine hearts that can be used with conventional immunosuppression regimens. Within a year, researchers expect to begin transplanting the organs into primates.

Transporting human hearts to new recipients is fraught with problems. The traditional way the heart is preserved and delivered for transplant is cold storage—flushing the heart with a solution that drops its core temperature, and then putting it in a picnic cooler with ice. This method can have limitations, due to organ decay, time, and distance of retrieval, resulting in the loss of many viable, transplantable organs. Now, seven hospitals are testing a novel device that could prevent this from happening by using a machine that replicates the heart functions as closely as possible while it’s in transit.

This “heart in a box” device is a wheeled cart with an oxygen supply, a sterile chamber, and tubing to clamp onto the donor heart and keep it fed with blood and nutrients. Doctors say this technology may extend the time a heart can last outside the body, and can even allow for the recovery of donor hearts that wouldn’t have been eligible in the past. Unlike the cold storage in a cooler, the heart in a box simulates the heart’s natural environment: It is kept warm; it’s beating, and it’s fed by a steady stream of oxygenated blood and nutrients. All the while, doctors are able to monitor the organ’s vitals.

If and when this device is approved in the U.S., it could expand the number of donated hearts by between 15 and 30 percent, saving the lives of people who would otherwise die from heart failure.

For more information about Dr. Madsen’s research, please contact Partners HealthCare Innovation by clicking here.