Selecting the right patients for artificial hearts

Arabia highlights various patient groups benefiting from TAHs, including those with severe biventricular failure, right heart failure, arrhythmias, post-infarction ventricular septal defects and amyloidosis. He stresses that TAH technology is typically reserved for the sickest patients, providing a lifeline while they await a transplant. Without long-term hemodynamic support, the patients would likely otherwise not survive to transplant.

These are five groups of patients typically considered for a TAH as a bridge to transplant:

   • Sickest patients with severe biventricular failure. He said these are patients who are often put on ECMO or temporary percutaneous ventricular assist device because of the severity of their end-stage heart failure. 

   • Patients with severe arrhythmia. Arabia said these patients often have been ablated multiple times and continue to have the arrhythmia. Patients with a left ventricular assist device (LVAD) where the arrhythmia is still not under control face an increased risk of experiencing right ventricle failure. 

   • Post-infarction caused ventricular septal defect (VSD). In some myocardial infarction patients, a perforation occurs where the muscle dies in the septum between the right and the left ventricle. Arabia said this can sometimes be repaired, but if they are a potential transplant candidate, it is much easier to put in a TAH and remove the damaged heart. 

   • Patients who have cardiac amyloidosis and are transplant candidates. When their condition deteriorates because the amyloid has infiltrated both ventricles and the inside of the heart has been compromised because there is too much accumulation, a TAH can help.

   • Patients who have congenital heart disease.

The current workhorse artificial heart

Arabia, who is deeply involved in the field, explained that the SynCardia artificial heart, a direct descendant of the Jarvik 7 from the 1980s, has been a crucial bridge to transplant for critically ill patients. The SynCardia, powered by compressed air, enables patients to lead a relatively normal life while awaiting transplantation.

The cost of a TAH ranges from $150,000 to $200,000, which is comparable to a heart transplant. Arabia notes that using a TAH as a bridge to transplant doubles the cost of care due to the requirement for two major operations.

This 30-year-old technology may soon be replaced by a new generation of artificial hearts currently being used in clinical trials.

Next-generation artificial heart technology

There has been a lot of interest in cardiology in the past couple years for two new TAHs entering the scene, the Carmat Aeson and BiVacor devices. The Carmat device, currently in FDA trials, features electro-mechanical components and an innovative design using bovine pericardium to minimize the need for anticoagulation. The BiVacor is unique in that it uses an electromagnetically levitated impeller as its only moving part. This feature also makes it completely silent and potentially reduces complications associated with traditional TAHs.

The newer artificial hearts only have one drive line, compared to two with the Syncardia device. 

The SynCardia is made out of polyurethane and the valves are metallic and pneumatically driven. In comparison, the Carmat TAH is electromechanically driven, pushing silicone oil between the left and the right ventricles in the pump. Each ventricle has a diaphragm and the inside of the diaphragms are covered with bovine pericardium. This organic material should enable minimize anticoagulation. 

Carmat reached 50 patients now implanted with its TAH in 2023. Three U.S. patients were implanted with a Carmat device until the trial was put on hold in 2022 due to device supply issues. Carmat has ccontinued its in-depth discussions with the FDA in order to use its EFS10 and ongoing EFICAS study data in France to enable the company to avoid undertaking a substantial U.S. pivotal study. The company said it hopes to apply for FDA premarket approval (PMA) by the end of 2026.

In November 2023, BiVacor received the green light from the FDA to begin its trial at U.S. centers. It's impeller is electromagnetically levitated and floats between the left and the right ventricle. 

"The incredible thing about it is that with no valves and with one impeller that moves, by applying oscillating electromagnetic impulses to the pump, you can generate a pulse by accelerating and decelerating the impulse. So here you have the most simplistic artificial heart, one moving part, no valves, producing aortic pulsation like if there was a natural heart," Arabia explained. 

Both devices are designed for a service life of between 10-20 years, which is about the same that can be expected from a transplanted heart.

He hopes these advances will make TAHs more accepted and more widely used in the next few years.

Barriers to artificial heart implants

Arabia admits the number of TAHs is low compared to the overall need for transplants and the long and growing patient waiting list for new hearts. He said the barriers are multifactorial. 

"Sometimes people are reluctant to use it because they think that their patient is going to expire or not do well. That's number one. Number two, the surgery is a little bit more involved and that has negatively impacted many surgeons who do not want to use it because it is a little bit more involved. So what we have done over the last 10, 15 years is actually to simplify the surgery, so implanting it and removing it is actually now fairly simple. So hopefully people will be able to understand that these barriers have been overcome. And now we have the ability to send those patients home," Arabia explained.

He said many healthcare providers complained that the current model of total artificial heart is noisy.

"It's usually the healthcare provider who tells me it's noisy and say they don't want to use it. The patients are glad to be alive and the family members are glad to have them," he said. 

Future or completely implanted devices without drivelines

All LVADs and artificial hearts in use and in trials use external drivelines to power the device. Because some of these do enable the patient to carry a bag with batteries to power the drivelines, the patient is permanently tethered to the drivelines. The way these lines move through the patient's skin can also be a source of infections.

Looking ahead, Arabia envisions future TAH devices will not require as much electrical power as they do now. When that power consumption drops, it will enable drivelines to be eliminated. Instead, transcutaneous power transmission devices with a wearable battery belt under the patient's clothing will power the device. This technology is already in development to use a power transmission pads under the skin and in the wearable battery pack to transfer power through the skin. This is the same technology now used by the newer generation iPhones where they can be charged by just setting them on a charging pad, rather than using a cord and plug. He said this will make make TAHs even more viable. He said new devices boasting longer lifespans may also help evolve TAHs into a more permanent alternative to heart transplantation.

Pig hearts rather than human heart transplants

Pig hearts are anatomically very similar to human hearts, which is why they are used to test new cardiac devices in translation research labs. There has been ongoing research for years on how to enable pig hearts to be used as a readily available supply for humans rather than needing extensive transplant waiting lists and admission requirements. This use of animal organs in humans is called a xenotransplant.

Surgeons at the University of Maryland Medical Center (UMMC) in Baltimore transplanted the first genetically modified pig heart into a human in January 2022. A second attempt was made in 2023. Both patients died within two months, but researchers said the lessons learned may help unlock this technology in the near future to enable an unending supply of off-the shelf transplant hearts. But Arabia feels this may be a viable option within the next decade and move from the realm of science fiction to daily clinical use.

"In the next 10 years, I'm hoping we will have patients with xenotransplants. A patient might start with an artificial heart and then 10, 15 years later we'll get a xenotransplant and then in the last part of their life will get a human transplant. I want to be optimistic that we will be able to overcome the barriers that have been identified, like the hypertrophy. There is no doubt that we still have some work to do," Arabia explained.

An even better option for exact patient-donor matches would be to use DNA from the patient to just grow a new heart in the lab and then transplant it into the patient. Or, he said cell therapies may be developed to fix a patient's existing heart and completely eliminate the need for transplants.

"I'm not too sure I'll be seeing that [in my lifetime], but at least we know that if someone is in ventricular failure at this point and a heart transplant is not available, an artificial heart is an option," he explained.