Trends in Mechanical Support Use as a Bridge to Adult Heart Transplant Under New Allocation Rules

Abstract

This study investigates trends in mechanical support use after implementation of the Organ Procurement and Transplantation Network’s new heart transplant allocation rules.

On October 18, 2018, new US adult heart transplant allocation rules were implemented by the Organ Procurement and Transplantation Network (OPTN). Updated rules were needed primarily to reduce significant overcrowding in the top-priority tier.^1,2 A key modification divided the prior status 1A into 3 categories (status 1-3), reserving status 1 for the sickest few, and created status 4 corresponding to prior status 1B.³ In this division, patients supported by durable left ventricular assist devices (LVADs) were largely redistributed to lower tiers, reflecting improved waitlist survival with continuous-flow LVADs over the last decade.⁴ Patients with most LVAD complications or within the 30-day LVAD discretionary window, previously assigned status 1A, were made status 3. Remaining LVAD-supported patients became status 4 unless they have device malfunction (status 2) or life-threatening ventricular arrhythmias (status 1). Conversely, the smaller number of transplant candidates requiring veno-arterial extracorporeal membrane oxygenation (VA-ECMO), typically for biventricular failure, retain status 1 listing if stringent criteria are met justifying VA-ECMO. While the goal of these changes was to redistribute donor hearts to patients at higher risk of pretransplant mortality,² the degree to which this has affected VA-ECMO or LVAD use as a bridge to transplantation is unknown.

Methods

We conducted a retrospective analysis of all adult patients in the OPTN registry listed for isolated heart transplant from January 1, 2014, to June 30, 2019, excluding retransplantation. We performed interrupted time series analysis to evaluate trends of VA-ECMO or dischargeable LVAD support at initial listing (defined via status justification forms with all data present) during each of 3 periods: (1) before the new allocation tiers were publicized in August 2016 (n = 8658),⁵ (2) after rule publication but prior to implementation (n = 7422), and (3) after implementation in October 2018 (n = 2599). The month of October 2018 overlapped both allocation systems and was treated as a transition period. Given that this is a publicly available, deidentified database, we obtained an institutional review board exemption from the University of Pennsylvania that also applied to patient consent. Linear mixed models were fit with center-level random slope and intercept along with first-order autoregressive errors to account for center effect and time-dependent autocorrelation. A 2-sided α of .05 was used.

Results

The percentage of patients supported by LVAD at listing had been stable since 2014 under both preimplementation periods but began decreasing under the new allocation rules, from 35.1% in November 2018 to 24.5% in June 2019 (Figure). Before rule publication, LVAD listings were increasing only 0.11% per month (95% CI, −0.007% to 0.2%; P = .07), and this slope decreased by only 0.10% after rule publication (95% CI, −0.32% to 0.12%; P = .37). After rule implementation, the slope decreased significantly by 1.44% per month compared with after publication (95% CI, −2.2% to −0.64%; P < .001).

Figure. Monthly Percentage of Heart Transplant Candidates Listed With Veno-Arterial Extracorporeal Membrane Oxygenation (VA-ECMO) or Durable Left Ventricular Assist Device (LVAD), 2014 to 2019.

Each dot represents the monthly percentage of transplant candidates supported by VA-ECMO or LVAD at the time of initial transplant listing in the United States from January 1, 2014, to June 30, 2019. The change in percentage per month (ie, slope) is displayed for the first period, and the change in slope compared with the immediate prior period is displayed for the second and third periods.

Conversely, the percentage of patients supported by VA-ECMO at listing had been decreasing slightly during both preimplementation periods but began increasing significantly after rule implementation, from 1.2% in November 2018 to 3.2% in June 2019. Before rule publication, VA-ECMO listings were decreasing 0.03% per month (95% CI, −0.06% to −0.009%; P = .008), and this slope was unchanged after rule publication (slope change, 0.04% per month; 95% CI, −0.01% to 0.09%; P = .17). After rule implementation, the slope increased significantly by 0.33% per month compared with after publication (95% CI, 0.10% to 0.56%; P = .005).

Discussion

Compared with the prior allocation system, the percentage of patients supported by durable LVAD at listing has been significantly decreasing while VA-ECMO percentages have been significantly increasing. These results suggest some exchangeability between initial support platforms, aligning with allocation incentives in spite of stringent listing criteria. These changes could be detrimental to waitlist or posttransplant outcomes if lower-acuity patients are prioritized for transplantation or if VA-ECMO support in the pretransplant period is itself directly harmful compared with LVAD. This study has several limitations associated with the use of a large retrospective database. However, this database is the largest and most comprehensive database for heart transplants in the United States and as such represents all patients transplanted in the United States and the criteria used to justify their listing status.