Giving hearts, and patients, longer lives with advanced technology
Expanded use of warm and cold perfusion techniques enlarges pool of transplant organs
Two innovative technologies – one hot, one cold – have made using hearts after circulatory death possible, tripling the length of time the organ is viable for transplant and expanding the pool of donor organs.
At a time when there are not enough donors to meet the need for heart transplants, warm and cold perfusion technology allows the UTSW Heart Transplant team to re-energize and restore hearts for transplantation, said Matthias Peltz, M.D., Professor of Cardiovascular & Thoracic Surgery and Surgical Director of Cardiac Transplantation and Mechanical Circulatory Support. These “heart in a box” devices maintain oxygen flow in the donor heart during transport, support energy metabolism, and extend the life of the tissue.
“Perfusion technologies are a significant change in heart transplantation,” Dr. Peltz said. “They have created a wider, deeper donor pool. Time is now less of a factor, and our patients can receive donor hearts from anywhere in the country. Hearts that once were unrecoverable due to distance or circulatory death can now give our patients a second chance.”
Warm and cold perfusion technologies have deepened the donor pool by 30%, nearly doubling the donor-to-transplant window and more than tripling the geographic area that donors can be accepted from, Dr. Peltz said.
In the past, donations came only from those declared brain dead whose hearts continued to function on life support. This preserved the organs until they could be packed on ice in a cooler for transport, giving medical teams only a three- to four-hour window to transplant the de-oxygenated heart. With these new technologies, machines keep the heart functioning significantly longer.
How warm perfusion works
In nearly a third of its heart transplant cases, UT Southwestern uses a warm perfusion, or beating-heart technology called the TransMedics Organ Care System. The technology was approved by the U.S. Food and Drug Administration (FDA) in 2021 for expanded criteria heart donation after brain death and extended in 2022 to include donation after circulatory death. For warm perfusion collection, the transplant team removes the donor heart and attaches it to the machine, which oxygenates the organ with a blood-based solution at a pressure of 60-90 mmHg – the normal pressure for an average adult. The oxygenated blood and pumping activity of the device reanimates the donor heart and restores the heartbeat while maintaining a temperature of 34 degrees Celsius (93 degrees Fahrenheit).
Once the heart is reanimated, the transplant team assesses its function and any structural nuances. Because the warm perfusion technology supports the heart, the organ isn’t burning through its own metabolic storages like it did in days when an Igloo cooler was used, Dr. Peltz said. This extends the recovery-to-transplant window from three to four hours to over 12 hours, which can make the difference between life and death for transplant recipients.
“Transplant teams can travel more than triple the distance to accept donor hearts, increasing our previous 1,000-mile radius to 3,500 miles,” Dr. Peltz said. “We can now receive hearts from anywhere in the continental U.S. and even Hawaii or Alaska.”
The warm perfusion technology is also used extensively for liver and lung transplants. It is also available for kidney donations. However, kidney transportation is less time-sensitive – the organs can remain viable out of the body for up to 72 hours with device support.
How cold perfusion works
With this technology, the donor heart does not beat in the box. Instead, it remains in an energy-neutral state. The heart is attached to the machine, where it is perfused with an oxygenated gas mixture (95% oxygen, 5% carbon dioxide). The heart is maintained at 8 degrees Celsius (about 46 degrees Fahrenheit), which has been shown to have better outcomes than transport at colder temperatures.
The XVIVO Heart Assist Transport cold perfusion technology received an FDA investigatory device exemption in 2023 for hearts from extended criteria donors and donors after circulatory death and is still being tested.
UTSW is participating in the PRESERVE Heart Study, a clinical trial to measure the safety and effectiveness of this technology for higher risk donors and donation after circulatory death among donors whose hearts have structural differences or risk factors for primary graft dysfunction (organ rejection by the recipient). This includes:
- Donors older than 50
- Heart-out-of-body time of more than four hours
- Donations after circulatory death
- Heart-out-of-body time of more than two hours with minimal acceptable risk factors such as thick heart tissue, lengthy death-to-resuscitation time, or minor coronary artery irregularities
UTSW enrolled the final recipient in November 2024. In November 2025, researchers from 20 institutions across the country will compare the outcomes in this study. It is anticipated XVIVO will seek approval for heart transplant centers that participated in the trial to continue using the system while it pursues FDA approval. So far, UTSW has not used this technology involving donor hearts recovered after circulatory death due to restrictions on how those hearts need to be recovered. As of Jan. 24, five UT Southwestern heart transplant recipients had received their donor hearts through cold perfusion as part of the PRESERVE study.
Extending the gift of life in North Texas
There is ongoing debate about whether warm or cold perfusion is preferred, but experts agree on one point, Dr. Peltz said.
“Transporting an oxygen-perfused heart is hands-down better than packing one on ice in an Igloo cooler,” he said. The importance of warm and cold perfusion technology is clear.
“More than 5,700 people in the U.S. are waiting for a heart, and 400 of them are on the Texas waitlist,” Dr. Peltz said. “Warm and cold perfusion technologies make it possible to give more patients with heart failure lifesaving heart transplants.”