Patients with advanced heart failure requiring ventricular assist device (VAD) therapy often exhibit a degree of right ventricular dysfunction. Nevertheless, most can be managed with left VAD (LVAD) implantation. Right ventricular dysfunction varies in severity and is difficult to predict, yet up to 20% of LVAD patients develop right ventricular failure. In such cases, TAH could offer an alternative support option. SynCardia Systems® has FDA approval for its TAH as a bridge to transplantation since 2004. Despite this, most transplant centers do not offer TAH to patients with severe biventricular dysfunction awaiting transplantation. Indeed, in US mechanical support registries, TAH comprises less than 2% of implanted VAD therapies, highlighting the limited use of the only FDA-approved device for biventricular dysfunction patients.

The article aims to evaluate the use and outcomes of TAH patients in the United States. Data from the UNOS (United Network of Organ Sharing Standard Transplant Research File) database were analyzed for all TAH implants in the US from 2005 to 2018.

Over this 13-year period, 471 patients with an average age of 47 years were treated with TAH, with males representing 87%. Among the 161 centers involved, 11 had performed more than 10 implants, classifying them as high-volume centers and accounting for nearly half of the studied cohort (212 patients). Patients treated at high-volume centers showed a higher incidence of renal failure requiring dialysis and worse hemodynamic parameters at implant time. A growing trend in TAH implants was observed, with a peak in 2013, followed by a gradual decline. High-volume centers generally had better outcomes. The cumulative incidence of mortality at 6 months and 1 year was 19% and 20%, respectively, for high-volume centers and 30% and 34% for others. The cumulative incidence of cardiac transplantation following TAH support at 6 months and 1 year was 51% and 65% at high-volume centers, and 47% and 58% at lower-volume centers. Finally, post-transplant mortality rates at 1 and 2 years after TAH therapy were 15% and 21% at high-volume centers compared to 25% and 31% at others. Cox multivariable regression analysis indicated that TAH implants at centers with fewer than 10 cases increased mortality during therapy (HR: 2.2; p < 0.001) and post-transplant mortality (HR: 1.5; p = 0.39).

The authors concluded that despite the low usage of TAH, it remains a valid bridging option for patients with severe biventricular dysfunction, particularly when performed at high-volume centers. The inferior outcomes observed at low-volume centers raise considerations for specialized training, certification, and minimum case volume requirements before initiating a program with this therapy.

COMMENTARY:
The SynCardia TAH is a pneumatic pulsatile pump used in cases of severe biventricular dysfunction. It is the only bridge-to-transplant device of its type approved by both the FDA and the European Union’s CE mark. The SynCardia technology builds on the Jarvik 7 platform, developed nearly 40 years ago. Copeland pioneered TAH as a bridge-to-transplant strategy after using the Jarvik 7 in a 25-year-old transplant-listed patient experiencing deterioration due to refractory ventricular arrhythmias in 1985. The success of this case led to the CardioWest Total Artificial Heart trial, published in 2004 by the same surgeon, which generated the evidence necessary for FDA approval. The trial compared TAH to a control group without circulatory support, demonstrating improved survival up to transplant (79% vs. 46%) and at one year (70% vs. 31%). Other TAH devices exist, including the AbioCor, approved for compassionate use as destination therapy in 2006 (with only one implant), and the CARMAT device, currently in clinical trials.

Despite Copeland’s 2004 findings, TAH use remains limited and is in decline. Notably, post-2013 outcomes appear worse than pre-2013. The Interagency Registry for Mechanically Assisted Circulatory Support’s overall results differ from the CardioWest trial, with a 59% transplant survival rate and a 34% one-year mortality incidence. The steep learning curve is evident, with one-year TAH survival rates at 72% in high-volume centers and 53% in others. This learning curve and disappointing results may contribute to TAH’s waning popularity. Some teams prefer more frequently used devices, implanting two HeartMate 3 devices (one per ventricle, off-label) or one HeartMate 3 for the left and one CentriMag for the right. Furthermore, UNOS’s revised priority criteria, which give short-term mechanical support patients the same or higher priority than long-term support patients, complicate TAH utilization. Finally, choosing TAH as therapy represents an irreversible decision, requiring either a transplant or, unfortunately, death while waiting, which complicates treatment decisions and acceptance of suboptimal organs once the decision is made.

This study has several limitations, including those inherent to its retrospective design. Using the UNOS database limits access to detailed information on major complications, such as stroke-induced neurological events. No control group was available for comparison, and patients in whom TAH was used as a bridge to candidacy are not captured in the UNOS database. Lastly, this study spans 13 years, encompassing multiple eras and protocol changes, necessitating caution in interpreting the results.

In conclusion, TAH is a therapy falling out of favor. In some countries, such as Spain, this therapy has not found its place. As the editorial to this article suggests, only time will tell whether TAH is forgotten or finds its niche.

REFERENCE:
Itagaki S, Toyoda N, Egorova N, Sun E, Lee T, Boateng Pet al. Total artificial heart implantation as a bridge to transplantation in the United States. J Thorac Cardiovasc Surg. 2024 Jan;167(1):205-214.e5. doi: 10.1016/j.jtcvs.2022.02.058.