Surgical Director of Cardiac Transplant
Department of Cardiovascular and Thoracic Surgery at UT Southwestern Medical Center
DALLAS – When a patient needs a heart transplant, time is of the essence. Two innovative technologies – one hot, one cold – can now keep the heart perfused outside the body, extending the organ’s viability for longer transports and expanding the pool of donor hearts.
As the heart pumps blood, it delivers oxygen and other nutrients throughout the body, including to the heart itself. When it stops, blood also stops circulating, depriving tissues of oxygen and making the heart potentially unsafe for transplant.
In the past, that meant transplant teams could not accept hearts for donation after circulatory death where the heart stopped. Instead, 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 an Igloo cooler for transport, giving medical teams only a 3-to 4-hour window to transplant the de-oxygenated heart.
This severely limited the number of donor hearts available and how far we could travel to collect them. But today, normothermic (warm) and hypothermic (cold) perfusion technologies have made transplants using hearts after circulatory death or from long distances not only possible, but also more the norm.
Warm and cold perfusion technology allows the UTSW Heart Transplant team to re-energize and restore hearts for transplantation. These “heart in a box” devices maintain oxygen flow in the donor heart during transport, supporting energy metabolism and extending the life of the tissue.
Perfusion technology has:
- Nearly doubled the donation-to-transplant timing window
- More than tripled the geographic area from where we can accept donations
- Deepened the donor pool by 30%
More than 5,700 people in the U.S. are waiting for a heart, and nearly 400 of them are on the Texas waitlist. Warm and cold perfusion technologies allow us to accept more donor hearts than ever before – so that we can give more patients with heart failure the lifesaving heart transplants they need.
Warm perfusion
UT Southwestern uses a warm perfusion, or beating-heart, technology called the TransMedics Organ Care System in nearly one third of our heart transplants. The technology was approved by the Food and Drug Administration (FDA) in 2021 for expanded criteria heart donation after brain death and expanded 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 perfuses (pumps through) the organ with an oxygenated, 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 reanimate the donor heart and restore the heartbeat while maintaining a temperature of 34 degrees Celsius (93 degrees Fahrenheit).
How it works
Once the heart is reanimated, we assess its function and any structural nuances. Because the warm perfusion technology supports the heart, the organ isn’t burning through its own metabolic stores like it did in the Igloo cooler days.
This extends the recovery-to-transplant window from 3-4 hours to over 12 hours, which can make the difference between life and death for transplant recipients in the case of unexpected delays or surgical complications. Transplant teams can travel more than triple the distance to accept donor hearts, increasing our previous 1,000-mile radius to 3,500 miles – we can now receive hearts from anywhere in the continental U.S. and even Hawaii or Alaska.
UTSW has set a threshold of acceptable time between circulatory death of the donor, organ recovery, and reanimation on the warm perfusion machine. Following our process, we have not yet had to turn down a heart donation after circulatory death. Clinical studies have shown that six-month outcomes for recipients of hearts after circulatory death are comparable to those of who received donor hearts after brain death.
In some cases, we can even keep the heart beating continuously when it is removed from the device and implanted into the recipient. By connecting the donor heart directly to a bypass machine, we can maintain the heart’s flow of life-sustaining energy from donor to recipient. Hearts in these cases tend to recover more quickly after transplant, with less need for pharmacological support.
Warm perfusion technology is also used extensively for liver and lung transplants. In fact, our liver team uses it for nearly every procedure. The technology 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.
Cold perfusion
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.
With this technology, the donor heart does not beat in the box. Instead, it remains in an energy-neutral state. The donor 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 shown to have better outcomes than transport at colder temperatures.
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
We enrolled our final recipient patient in November 2024, and we are observing three primary data points: 30-day survival, occurrence of primary graft failure, and one-year survival. In November 2025, researchers from 20 institutions across the country will compare the outcomes data in this study to established benchmarks to understand whether the device meets those criteria. From there, we anticipate that XVIVO will seek approval for heart transplant centers that participated in the trial to continue using the system while it pursues FDA approval.
Extending the gift of life in North Texas
There is ongoing debate about whether warm or cold perfusion is preferred. But experts can agree on one point for certain: Transporting an oxygen-perfused heart is hands-down better than packing one on ice in an Igloo cooler.
Perfusion technologies are a game-changer in heart transplantation. They’ve created a wider, deeper donor pool. Time is now less of a factor, and UTSW 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.
The timing couldn’t be better. The rate of heart transplantation across the U.S. increased 13 years straight from 2011 to 2024, and in 2024, there were nearly 800 heart transplants involving donors after circulatory death, more than three and a half times greater than the number in 2021, according to federal transplant data. Thanks to warm and cold perfusion technology, thousands more families can now choose to extend the gift of organ donation to patients waiting for a new heart.
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