Selena S. Li, MD: The US Heart Allocation System and Transplant Bridge Devices

Selena S. Li, MD

A new assessment from a team at the Massachusetts General Hospital (MGH) sought to interpret the effects of the current US heart donor allocation system on the use of mechanical circulatory supports (MCSs) as a transplant bridge.

The findings, to be presented in 2 parts this month at the International Society for Heart and Lung Transplantation (ISHLT) 2022 Meeting and the American Thoracic Society (ATS) 2022 Meeting, provide insight into the intersection of modernized donor allocation strategies and innovations in heart-supporting devices as clinicians become more capable of keeping fatal disease and events at bay in transplant-eligible patients.

In an interview with HCPLive, study author Selena S. Li, MD, a general surgery resident with MGH, discussed her team's findings as presented at ISHLT, the current state of US heart donor allocation, and the methods by which heart transplanted can be further improved relative to cardiac innovations.

HCPLive: Could we talk first and foremost about the current standard of the US heart allocation system practice, relative to previous iterations: how has it changed?

Li: In short, the previous iteration was a three-tiered system, categorizing patients into status 1A, status !B, or status 2, based on the acuity of their situation, the type of mechanical circulatory support and additional comorbidities. And in 2018, that changed to a six-tiered system—so, status 1-6. That aimed to provide increasing granularity to some of the previous tiers, and then also adjusted some of the locations. And so, what we focused on in particular was the effect of this on patients with durable left ventricular assist devices.

So previously, under the old allocation system, patients who were stable on a durable LVAD were status 1B, with the option to bump up to a status 1A for a 30-day exception or for any left ventricular-assisted device (LVAD)-related complications. And so this encompassed all ranges of complications. And under the new system, the aim was to categorize these into different buckets. Patients who were stable on durable LVAD support would then classified as status 4, with the option to bump the status 3 under the 30-day exception. And the types of complications were then categorized as status 1, 2 or 3, based on severity.

Regarding MCS's and their evolution in recent years, what exactly does that look like? And what's the current standard for VAD or total artificial heart (TAH) allocation? Who are our ideal patients, and at what stages of disease are we targeting them?

I think that's still sort of a nuanced question, and it depends largely on the clinician in the in the center implanting the devices. But I will say that the durable LVADs, the newer generations, have increasing durability. So, patients are able to be supported with a durable LVAD with good outcomes for 1-2 years with about 80-90% survival rates compared to previous generations in which that mortality was much more limited. And so, the new allocation system reflects this change in bumping down the priority of durable LVAD patients because they have improved survival. In contrast, there are significant advances in temporary mechanical circulatory support devices as well, such as the Impella.

So, in older generations of Impella, which is a temporary LVAD, they were able to provide some sort of partial circulatory support. But the newer version of impella—the Impella 5.5, which you can implant via axillary access—that is able to provide full circulatory support. So it provides an interesting alternative to durable LVADs.

Regarding your team's research, what really stood out to you as the most significant findings from this assessment?

We actually conducted 2 parallel studies. The second is being presented at ATS in the next couple of weeks. And the first is what you referred to which is presented at ISHLT. One study focused on the effects of the new allocation system on durable LVAD patients only, pre- and post-allocation change. And that's what will be presented at ATS. And we found that after the allocation change, patients with durable LVADs had worse post-transplant survival outcomes. But this was largely attributed to a difference in patient population. Because of the lower priority status of these patients, only the sickest patients, or patients who are willing to accept more marginal donor offers, are those who are being transplanted. As a result, you see worse transplant survival outcomes.

As a parallel, we looked at durable LVAD versus temporary LVAD patients under the new allocation system. What we saw is that temporary LVAD patients had improved survival compared to durable LVAD patients. But again, we suspect that this is largely due to differences in donor offers. Temporary LVAD patients spent less time on the waitlist, were transplanted at higher priority waitlist statuses, and had overall lower numbers of the donor sequence number, which reflects the how far down you have to go on the waitlist in order to receive a donor offer.

For these reasons, and probably additional factors that were not accounted for in the database, we saw that temporary LVAD patients had improved survival compared to durable LVAD patients and that this could be an interesting alternative as a bridge to transplant.

From your perspective, and relevant to these findings, what are some tangible approaches we could be taking to continue to improve our transplant allocation strategies for our patients?

I think that's definitely an important question and one that's difficult to answer without considering everything that goes into donor availability. I know there are efforts in increasing the donor pool, whether that is accepting more marginal donor offers such as hepatitis C-donor organs, which our group has previously shown to have comparable outcomes to hepatitis C-negative offers. That's one way to expand the donor pool. The other is using donation after cardiovascular death, so DCD hearts with new transport devices such as the transmatic device—which allows you to take a DCD heart, which was previously not able to be used for heart transplant, reperfuse the heart in transport with normothermic perfusion. That's basically placing the heart on a pump, and allowing that heart to recover, and then to implant the recovered heart into a recipient. That would definitely change the game in terms of expanding the number of offers that are available.

And then the final piece is on the recipient side, making sure that we are giving the hearts to the patients who need it the most—understanding that's a very nuanced question. And I think that that is what the new allocation system is getting at.

Despite our studies, which show worse survival for the durable LVAD patients, I think it is still too early to say that the allocation system has had negative effect or positive effect. It's still quite early, and new studies need to be done as we have more data to see what the effects of the current allocation change are, in terms of affecting waitlist mortality and post-transplant mortality. So, I think from multiple funds, there are things that we can do to both expand the donor pool as well as to make sure that we're allocating the organs to the correct patients.