Temporary Mechanical Circulatory Support Use and Clinical Outcomes of Simultaneous Heart/Kidney Transplant Recipients in the Pre– and Post–Heart Allocation Policy Change Eras : Transplantation

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Original Clinical Science—General

Temporary Mechanical Circulatory Support Use and Clinical Outcomes of Simultaneous Heart/Kidney Transplant Recipients in the Pre– and Post–Heart Allocation Policy Change Eras

Agdamag, Arianne C. MD1; Riad, Samy MD2; Maharaj, Valmiki MD1; Jackson, Scott MS3; Fraser, Meg DNP, NP-C1; Charpentier, Victoria BS4; Nzemenoh, Bellony MD5; Martin, Cindy M. MD1; Alexy, Tamas MD, PhD1

Author Information
Transplantation ():10.1097/TP.0000000000004518, January 19, 2023. | DOI: 10.1097/TP.0000000000004518
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Abstract

INTRODUCTION

Heart transplantation remains the gold-standard therapy for qualified candidates with end-stage heart failure (HF). Although the annual volume of donor hearts accepted for transplantation only increased marginally in the United States during the past decade, the number of patients with high-priority listing status has tripled, exception requests soared, and waitlist mortality increased significantly.1 These unfavorable trends prompted the development of a new US donor heart allocation system by the United Network for Organ Sharing (UNOS) that was implemented on October 18, 2018. The policy change aimed at providing a more granular risk stratification of potential recipients and prioritizing organ offers to those with the most urgent need to reduce waitlist mortality.2

The new system gives priority, with stringent criteria and time constraints, to waitlisted patients requiring a temporary endovascular mechanical circulatory support (tMCS) device, such as intra-aortic balloon pump (IABP; status 2), Impella (Abiomed Inc, Danvers, MA; status 2) or venoarterial extracorporeal membrane oxygenation (VA-ECMO; Centrimag, Abbott, Chicago, IL, and Cardiohelp, Maquet, Rastatt, Germany; status 1). Utilization of tMCS systems has increased significantly in transplant centers across the United States for heart-alone transplant candidates after the UNOS allocation policy change.3-8 Despite initial concerns, several recent reports have shown that this change in clinical practice had no detrimental effect on survival rates, nonfatal major cardiac events, freedom from cardiac allograft vasculopathy, or the incidence of rejection after heart-alone transplantation (HAT) at 1 y.7-11

Renal dysfunction is relatively common in patients with end-stage HF owing to the cardiorenal syndrome, recurrent episodes of acute kidney injury, and high-dose diuretic requirements.12,13 Given its association with poor clinical outcomes, many centers use an estimated glomerular filtration rate (eGFR) of 30 mL/min as a relative contraindication to HAT14-16 and as the threshold to consider simultaneous heart-kidney (SHK) transplantation for appropriate candidates.17-20 The potential clinical practice changes in SHK candidates, driven by the UNOS heart allocation update, and their effect on clinical outcomes remain unexplored.

The primary aims of the present study were to contrast tMCS utilization in adult SHK candidates before and after October 2018 and to compare recipient survival up to 1 y in the 2 eras. Secondary aims included survival rates specific to tMCS devices at 1 y post-SHK and changes in SHK waitlist mortality in response to the heart allocation policy update.

MATERIALS AND METHODS

Data Source

This study used data from the Scientific Registry of Transplant Recipients (SRTR). The SRTR data system includes data on all donors, waitlisted candidates, and transplant recipients in the US, submitted by the members of the Organ Procurement and Transplantation Network. The Health Resources and Services Administration, US Department of Health and Human Services provides oversight of the activities of the Organ Procurement and Transplantation Network and SRTR contractors. All authors were approved to participate in the current project by the SRTR. This study was exempted by the Institutional Review Board of the University of Minnesota. All authors were approved to participate in the current project by the SRTR.

Study Population and Data Analysis

A detailed study enrollment flowchart is presented in Figure 1. First, we identified all adults (age ≥18 y) who underwent primary SHK between January 2010 and March 2022. Subsequently, recipients supported with one of the following tMCS devices before transplantation were selected: (1) VA-ECMO; (2) Impella 2.5, CP, 5.0; and (3) IABP. Those with any other pretransplant mechanical circulatory support strategy, including a durable left ventricular assist device, such as the HeartMate XVE, HeartMate II, HeartMate III (Abbott Laboratories, Minneapolis, MN), or HeartWare (Medtronic Inc, Minneapolis, MN), were excluded. Prior heart or kidney transplant recipients and those listed in both allocation periods were also excluded. Outcomes from this test cohort were compared with SHK recipients with no pretransplant device support in both the current and prior heart allocation eras. Impella 5.5 was not yet routinely coded in the most recent SRTR source file.

F1
FIGURE 1.:
Patient enrollment flowchart. “Other ineligible tMCS support devices” included support systems such as total artificial heart or TandemHeart. ECMO, extracorporeal membrane oxygenation; IABP, intra-aortic balloon pump; LVAD, left ventricular assist device; SHK, simultaneous heart-kidney transplantation; tMCS, temporary mechanical circulatory support.

Demographic information, the annual number of SHK transplants, tMCS utilization, recipient survival rates, and final urgency listing with the time accrued in each status were reviewed (status 1A, 1B, or 2 before the policy change and status 1–6 subsequently). Kaplan–Meier analysis was performed to compare 1-y survival rates of SHK recipients transplanted in the eras before and after the heart allocation policy update. Aiming to provide a general overview, this initial comparison included all SHK recipients independent of tMCS support or urgency listing status.

Next, Kaplan–Meier curves were generated to compare 1-y post-SHK survival of recipients supported with any of the eligible intravascular tMCS devices (peripheral VA-ECMO, Impella, or IABP) in the 2 heart allocation policy eras.

Subsequent analyses were restricted to the current heart allocation era, given the prolific increase in tMCS use after October 2018 to bridge candidates to SHK transplantation and its relevance to patient management. First, we compared the survival of recipients who were transplanted from urgency status 1 and 2 with a tMCS to those without a circulatory support device (no tMCS + status 1/2 group) at 1 y. Recognizing, however, that posttransplant outcomes may be affected by the level of hemodynamic support required before the surgery, survival rates specific to individual tMCS devices were contrasted and also compared with SHK recipients transplanted from the respective urgency statuses but without device support.

Finally, we performed a separate analysis comparing SHK candidate waitlist mortality before and after the heart allocation policy update. A detailed explanation of the complex methodology is provided in tandem with the results next.

Statistical Analysis

Baseline characteristics between the pre– and post–heart allocation change groups were compared with the chi-square or Fisher test for categorical variables and t test for continuous variables. Data are presented as mean ± SD for continuous variables and number (percentage) for categorical variables. Kaplan-Meier analysis with log-rank tests was performed to compare all-cause mortality between subgroups, censored at 1 y posttransplant. A Cox proportional hazards model was used to further investigate the effect of allocation period on patient survival up to 1 y, adjusted for the following covariates: recipient age, body mass index (BMI), black race, recipient-donor race match, pretransplant dialysis, total serum bilirubin, diabetes, the need for inotrope infusion, mechanical ventilator use, intensive care unit level of care at time of transplant, donor LVEF >50%, cytomegalovirus (CMV) serostatus, and heart total ischemia time (in minutes). Transplant center was considered as a random effect. Statistical analyses were performed using R version 4.2.1.

RESULTS

A total of 1548 adults with no prior heart or renal transplant were identified from the SRTR database who either underwent SHK between January 1, 2010, and September 30, 2018, or listed and transplanted between November 1, 2018, and March 2, 2022. Of these, 337 had a durable left ventricular assist device, and 109 had another ineligible tMCS device, such as total artificial heart (SynCardia, Tucson, AZ) or TandemHeart (LivaNova PLC, Houston, TX), and thus were excluded from further analysis by study design. The final cohort included 1102 SHK recipients, with 534 surgeries performed before and 568 after October 2018 (Figure 1).

There was a continuous growth in the annual number of SHK transplants during the study period with the most profound increase after 2018 (Figure 2). Data for 2022 were censored on March 2, 2022. As anticipated on the basis of previously published HAT data, the proportion of SHK candidates supported by tMCS increased each year after October 2018, as illustrated by the light gray area of the corresponding columns in Figure 2. Although numerically, the expansion in IABP use was the most prominent after the heart allocation policy update, Impella and VA-ECMO utilization also grew significantly (P < 0.001; Table 1 and Figure 3).

TABLE 1. - Simultaneous heart-kidney transplantation recipient characteristics in the pre– and post–heart allocation change eras, full cohort
Variable Preallocation change (n = 534) Postallocation change (n = 568) P
Recipient age, y 57 ± 10 57 ± 10 0.85
Male sex 424 (79) 445 (78) 0.72
BMI, kg/m2 26.4 ± 4.8 26.5 ± 5.0 0.59
Race 0.12
 African American 173 (32.4) 208 (36.6)
 White 327 (61.2) 314 (55.3)
 Other 34 (6.4) 46 (8.1)
Blood group 0.67
 A 210 (39.3) 219 (38.6)
 AB 29 (5.4) 40 (7.0)
 B 98 (18.4) 96 (16.9)
 O 197 (36.9) 213 (37.5)
Diabetes 231 (44.2) 243 (44.0) 1.00
eGFR, mL/min 30.1 ± 23.0 37.1 ± 25.9 <0.001
On dialysis pretransplant 226 (42.4) 216 (41.2) 0.44
Dialysis between transplant and discharge 143 (27.0) 183 (35.1) 0.005
Recipient total bilirubin 1.27 ± 3.58 1.19 ± 2.72 0.68
Etiology of heart failure 0.003
 Congenital 9 (1.7) 8 (1.4)
 Ischemic 239 (45.3) 202 (36.4)
 Nonischemic 252 (47.7) 309 (55.7)
 Restrictive 28 (5.3) 36 (6.5)
Inotrope infusion at transplant 345 (64.6) 270 (51.2) <0.001
Mechanical ventilator at transplant 5 (0.9) 12 (2.3) 0.135
VA-ECMO, Impella, or IABP support 96 (18.0) 293 (51.6) <0.001
Urgency status 1A/1B/2 70.4%/24.9%/4.7% NA NA
Urgency status 1/2/3–6 NA 12.5%/58.1%/29.4% NA
Average time in final urgency listing status, d 54 ± 107 24 ± 48 <0.001
Total heart ischemic time, min 181 ± 56 204 ± 56 <0.001
Donor age, y 33 ± 11 32 ± 10 0.48
P values <0.05 are significant.
Values presented are n (%) or mean ± SD.
BMI, body mass index; eGFR, estimated glomerular filtration rate; IABP, intra-aortic balloon pump; NA, not available; VA-ECMO, venoarterial extracorporeal membrane oxygenation.

F2
FIGURE 2.:
Annual number of SHKs in the United States between 2010 and 2022. The light gray area of the columns illustrates the number of SHK candidates supported by a tMCS device each year. Data for 2022 were censored on March 2, 2022. SHK, simultaneous heart-kidney transplantation; tMCS, temporary mechanical circulatory support.
F3
FIGURE 3.:
tMCS utilization in SHK candidates in the pre– and post–heart allocation change eras. A considerable growth was demonstrated in each device usage after October 2018. IABP, intra-aortic balloon pump; SHK, simultaneous heart-kidney transplantation; tMCS, temporary mechanical circulatory support; VA-ECMO, venoarterial extracorporeal membrane oxygenation.

Baseline characteristics for the full pre– and post–heart allocation change SHK groups are detailed in Table 1. There was no significant difference in recipient age, race, gender distribution, BMI, blood group, incidence of diabetes, pretransplantation dialysis need, mechanical ventilator use, and total serum bilirubin level. The mean donor age was also similar. However, recipient mean eGFR was higher in the current allocation era (30.1 ± 23.0 versus 37.1 ± 25.9 mL/min; P < 0.001), whereas inotrope use was less frequent (64.6% versus 51.2%; P < 0.001). The most common cause for end-stage HF shifted toward nonischemic causes (P = 0.026), consistent with the general trend in the HF population at large.21 The majority of candidates underwent SHK from urgency status 1A (70.4%) before and status 2 (58.1%) after the allocation policy change, with the average time spent in the last urgency status decreasing from 54 to 24 d (P < 0.001). The total donor heart ischemic time increased from 181 to 204 min (P < 0.001; Table 1). Kaplan–Meier survival analyses of the final SHK cohort are depicted in Figure 4. Despite the significant modifications to the heart allocation scheme and change in peritransplant clinical management strategies, 1-y post-SHK survival rates were high and unaffected (89.3% versus 86.5%; overall log-rank P = 0.154). One-year recipient survival remained similar between the allocation periods after adjustments for covariates listed above in a Cox proportional hazards model (postallocation hazard ratio [HR]: 1.07 [0.716-1.603], P = 0.737; Table 2). Higher recipient age (HR: 1.027 [1.005-1.05], P = 0.015) and BMI (HR: 1.051 [1.009-1.094], P = 0.016) were both associated with increased risk of mortality with 1 y.

TABLE 2. - Cox proportional hazards model for 1-y patient survival
Variable Hazards ratio Confidence interval P
Post-allocation 1.071 0.716-1.603 0.737
Recipient age, y 1.027 1.005-1.05 0.015
Recipient BMI, kg/m2 1.051 1.009-1.094 0.016
Recipient Black race 0.873 0.562-1.358 0.548
Race match 0.919 0.607-1.393 0.692
Cold ischemic time, min 1.001 0.998-1.005 0.469
Recipient diabetes 0.824 0.557-1.220 0.333
Total serum bilirubin 1.007 0.953-1.064 0.810
Pretransplant dialysis 1.131 0.762-1.678 0.542
Recipient in ICU pretransplant 1.245 0.817-1.897 0.308
Recipient on inotrope at transplant 0.692 0.471-1.017 0.061
Recipient on ventilator pretransplant 1.861 0.578-5.998 0.298
Donor LVEF >50% 1.627 0.590-4.487 0.347
Donor CMV positive 0.668 0.457-0.976 0.037
P values <0.05 are significant.
BMI, body mass index; CMV, cytomegalovirus; ICU, intensive care unit; LVEF, left ventricular ejection fraction.

F4
FIGURE 4.:
Kaplan–Meier survival analysis of simultaneous heart-kidney transplantation recipients (n = 1102) in the pre– and post–heart allocation policy change eras. Candidates with prior heart or kidney transplant and those with a durable left ventricular assist device or other ineligible devices were excluded. There was no significant difference in 1-y survival.

Of the 389 candidates supported with a tMCS device before SHK, 96 underwent transplantation in the prior and 293 in the current heart allocation period. Demographics were similar between groups (Table 3). Pre-SHK dialysis need, mechanical ventilator use, and inotrope infusion were also comparable. Although mean eGFR values were not statistically different between candidates managed with tMCS in the 2 heart allocation eras (37.6 ± 27.3 versus 41.6 ± 28.0 mL/min; P = 0.225), these were both higher than the eGFR in the respective cohorts without device support (28.5 ± 21.6 and 31.6 ± 21.8 mL/min, respectively). This finding suggests that pretransplant tMCS device use may potentially help maintain end-organ perfusion and thus function in this critically ill population. Essentially, all SHK candidates (99.0%) were transplanted from urgency status 1A before the allocation change and from status 1 or 2 (98.0%) in the current era. The policy update led to a significant reduction in the wait time spent in the final pretransplant urgency status from 35 to 13 d for those supported with tMCS (P < 0.001) and donor heart ischemic time increased from 184 to 206 min (Table 3). Kaplan–Meier analysis restricted to candidates supported with VA-ECMO, Impella, or IABP before SHK revealed similar 1-y survival rates in the pre– and post–heart allocation policy change eras (84.3% versus 86.1%; overall log-rank P = 0.784; Figure 5).

TABLE 3. - Simultaneous heart-kidney transplantation recipient characteristics in the pre– and post–heart allocation change eras, cohort managed with a temporary mechanical circulatory support device pretransplant
Variable Preallocation change (n = 96) Postallocation change (n = 293) P
VA-ECMO 20 (20.8) 57 (19.5) 0.64
Impella 2.5, CP, or 5.0 9 (9.4) 38 (13.0)
IABP 67 (69.8) 198 (67.6)
Recipient age, y 56 ± 12 57 ± 10 0.34
Male sex 83 (86.5) 241 (82.3) 0.42
BMI, kg/m2 26.8 ± 4.6 26.8 ± 5.0 0.93
Race 0.67
 African American 33 (34.4) 115 (39.2)
 White 57 (59.4) 159 (54.3)
 Other 6 (6.2) 19 (6.5)
Blood group 0.53
 A 31 (32.3) 102 (34.8)
 AB 7 (7.3) 13 (4.4)
 B 12 (12.5) 48 (16.4)
 O 46 (47.9) 130 (44.4)
Diabetes 49 (51.0) 119 (41.6) 0.14
eGFR, mL/min 37.6 ± 27.3 41.6 ± 28.0 0.23
On dialysis pretransplant 46 (48.4) 140 (47.8) 1.00
Temporary dialysis posttransplant 29 (31.2) 114 (39.2) 0.206
Recipient total bilirubin, mg/dL 1.29 ± 1.70 1.28 ± 2.17 0.964
Etiology of heart failure 0.06
 Congenital 1 (1.0) 2 (0.7)
 Ischemic 47 (49.0) 98 (33.8)
 Nonischemic 43 (44.8) 169 (58.3)
 Restrictive 5 (5.2) 21 (7.2)
Inotrope infusion at transplant 49 (51.0) 170 (58.0) 0.281
Mechanical ventilator at transplant 3 (3.1) 11 (3.8) >0.99
Average time in final urgency listing status, d 35 ± 39 13 ± 14 <0.001
Total heart ischemic time, min 184 ± 47 206 ± 55 0.001
Donor age, y 31 ± 10 31 ± 10 0.86
P values <0.05 are significant.
Values presented are n (%) or mean ± SD.
BMI, body mass index; eGFR, estimated glomerular filtration rate; IABP, intra-aortic balloon pump; VA-ECMO, venoarterial extracorporeal membrane oxygenation.

F5
FIGURE 5.:
Survival analysis of simultaneous heart-kidney transplantation recipients bridged with a temporary mechanical circulatory support device (intra-aortic balloon pump, Impella family, or peripheral venoarterial extracorporeal membrane oxygenation) in the pre– and post–heart allocation policy change eras. Candidates with prior heart or kidney transplant and those with a durable left ventricular assist device or other ineligible devices were excluded. There was no significant difference in 1-y survival.

The final analyses were restricted to the updated heart allocation era as it is the most relevant for current clinical practice. We found no significant difference in the 1-y survival of 293 SHK recipients managed with one of the eligible tMCS devices and the 114 individuals listed as status 1 or 2 but without a mechanical circulatory support strategy (86.1% versus 90.1%; overall log-rank P = 0.382; Figure S1, SDC,https://links.lww.com/TP/C685). Candidates with pretransplant IABP had similar 1-y outcomes compared with those listed in urgency status 2 but without IABP, suggesting that IABP use does not adversely impact survival (89.1% versus 89.7%; overall log-rank P = 0.966; Figure S2, SDC,https://links.lww.com/TP/C685). Finally, device-specific outcomes in the current allocation era were compared (Figure 6). Although there seems to be a signal for increased upfront risk during the initial 2 posttransplant months for those bridged with VA-ECMO or Impella, survival curves become essentially parallel subsequently with no statistical difference in survival rates at 1 y (overall log-rank P = 0.137).

F6
FIGURE 6.:
Survival of simultaneous heart-kidney transplantation recipients bridged with veno-arterial ECMO, IABP, Impella 2.5, CP or 5.0, and those listed as urgency status 1 or 2 but without a temporary mechanical circulatory support device. Although there is a trend for increased early mortality after simultaneous heart-kidney transplantation in those supported with venoarterial ECMO and Impella pretransplant, the overall 1-y survival rates were not significantly different. Data analysis was restricted to the current heart allocation policy era. ECMO, extracorporeal membrane oxygenation; IABP, intra-aortic balloon pump.

Waitlist Mortality of SHK Candidates

Owing to the inherent limitations of UNOS data collection (ie, the lack of a single SHK listing form that exists for other organ combinations), determining and comparing SHK waitlist mortalities in the 2 allocation eras is not straightforward. First, we had to define SHK listing for the purposes of this analysis. Given that in our data set, the majority of candidates were listed for the 2 organs within 1 d, we used this criterion to define the cohort of SHK listing. Next, we identified first-time adult SHK candidates who were listed between January 1, 2010, and September 30, 2018 (prior era, n = 914) or between November 1, 2018, and March 2, 2022 (new allocation era, n = 988). Patient follow-up was censored if any of the following events occurred: (1) removal from the waitlist for any reasons other than death, most commonly owing to a change in medical condition; (2) still listed at the predefined censoring date of September 30, 2018, for the prior- and March 2, 2022, for the current heart allocation era; (3) remaining on the waitlist at 1 y. The candidate was considered to have an event if death occurred before reaching any of the above-mentioned censoring criteria. A transplant of any type was considered a competing risk.

Subsequently, we performed a competing risks analysis to estimate the cumulative incidence of both mortality (event) and transplant (competing risk) using the Fine-Gray methodology using the cuminc function from the cmprsk package in R. The vast majority of transplant events were SHK (86.5%) or heart-alone (12.8%).

Figure 7 displays the incidence of mortality and successful transplant of candidates waitlisted for SHK in the pre– and post–heart allocation change eras. Waitlist mortality curves separated after 1.5 mo with significantly lower mortality within 1 y of SHK listing in the new heart allocation system (P = 0.002). One-year mortality was 10.1% in the pre-era compared with 6.1% in the postallocation change period. At the same time, there was a significant overall increase in transplant (P < 0.001). The incidence of transplant within 1 y was 59.1% in the prior and 71.8% in the current heart allocation era.

F7
FIGURE 7.:
Simultaneous heart-kidney transplantation waitlist mortality and transplant in the pre– and post–heart allocation policy change eras (censored at 1 y), estimated using the methodology of Fine and Gray. Simultaneous heart-kidney transplantation listing was defined as a candidate listed for both heart and kidney within 1 d of each other. There was a significant increase in transplant and a decrease in mortality under the current heart allocation system.

DISCUSSION

Our study demonstrates that, in patients supported with tMCS pre-SHK transplant, 1-y survival rates after SHK remained high and were not adversely affected by the heart allocation policy revision that took effect on October 18, 2018. The finding remained even after multivariable adjustments using the Cox proportional hazards model. Similar to published reports limited to HAT candidates, we found a profound increase in tMCS utilization as a strategy to bridge SHK candidates to transplantation in the current heart allocation era. The growth in IABP use was the most significant, and it did not adversely affect post-SHK survival.

Individuals with end-stage HF often suffer from concomitant renal dysfunction, a comorbidity that is associated with adverse clinical outcomes. The evolution of medical knowledge, immunosuppressive strategies, surgical techniques, technology, and the improved collaboration between the cardiac and renal transplant teams made SHK a feasible option for this growing patient population. Based on the International Society for Heart and Lung Transplantation recommendations published in 2016, an eGFR of <30 mL/min and dialysis dependency should serve as contraindications to HAT listing.16 More recent data from our group were in alignment with the aforementioned recommendations from International Society for Heart and Lung Transplantation and, in fact, suggest that patients with an eGFR of <40 mL/min at the time of evaluation should be considered for SHK rather than HAT.22 Recognizing the associated survival benefit, the overall number of SHK has increased significantly during the past years,23,24 which was redemonstrated in our analysis (Figure 2). However, donated human organs remain a scarce resource and judicious allocation to candidates who are anticipated to derive the most clinical benefit remains the utmost priority.25,26

The introduction of the highly anticipated donor heart allocation policy update in October 2018 prompted a profound change in clinical practice in transplant centers across the United States. Several reports indicated a significant increase in tMCS use as a bridging strategy among candidates waitlisted for HAT.7,10 Although initiating and maintaining tMCS device support is not without substantial risks and potential complications, such as bleeding, hemolysis, infection, critical limb ischemia, right HF, stroke, and the need for invasive procedures potentially under general anesthesia, recent reports on increasingly larger populations suggest that 1-y survival after HAT remained unchanged with the heart allocation policy update.7,10 We hypothesized that the evolution of clinical practice related to tMCS use affected the pretransplant management of SHK candidates similarly, and we thought to evaluate the clinical outcomes of this population at 1 y.

As anticipated on the basis of published HAT data, we found a significant increase in tMCS utilization to bridge patients to SHK in the revised heart allocation era. Importantly, this change in clinical practice pattern did not impact posttransplant survival at 1 y, even when performing granular comparisons between recipient groups transplanted from the same urgency status with or without tMCS. Although IABP provides the least amount of hemodynamic support, it may be initiated rapidly at the bedside or in the cardiac catheterization laboratory. The associated complication rate is relatively low and enables patient mobility when inserted through a subclavian or axillary approach. Accordingly, it is the most frequently used tMCS device among SHK candidates in the current heart allocation era. A dedicated analysis showed no adverse effect on posttransplant survival with IABP use at 1 y.

One notable observation in our study is the mean eGFR at the time of transplant was significantly higher in SHK recipients supported with a tMCS strategy when compared with the no device group. This trend was noted in the prior (37.6 ± 27.3 versus 28.5 ± 21.6 mL/min) as well as the current heart allocation era (41.6 ± 28.0 versus 31.6 ± 21.8 mL/min). Although the exact reasons remain obscure, we hypothesize that support with a tMCS device improves systemic blood pressure, renal perfusion, and alleviates cardiorenal syndrome. The lack of more granular data in the SRTR source file, such as vital signs or vasoactive-inotrope score at the time of transplant, precludes further analysis. However, similar findings have been reported previously by other investigators in SHK candidates.27 It remains unclear if using a tMCS support strategy before transplant would potentially facilitate renal recovery in HAT recipients with impaired kidney function. However, better renal function immediately before transplantation may have a positive influence on post-SHK outcomes.

Our comparison of SHK waitlist mortality in the pre– and post–heart allocation change periods revealed a significant decline in mortality in the current era, with the survival curves separating after 1.5 mo. This likely reflects the significant decrease in the average time spent in the final urgency listing status with the highest-risk patients undergoing transplantation earlier. Although longer follow-ups with larger population will be needed, these findings suggest that the heart allocation policy update led to a significant decline in SHK waitlist mortality, as intended by UNOS.

The findings in our article are of great importance to the transplant community. Organ availability for transplantation remains scarce and ensuring excellent long-term outcomes, especially following a policy change that affects routine clinical practice, is of utmost importance. When deciding on the use of tMCS in candidates listed for SHK, it is critical to know that providing extra hemodynamic support with any of the examined devices will not negatively impact recipient survival. Especially as we predict a further increase in tMCS use as bridge to transplant strategy in the current heart allocation era. However, further studies are needed, using data from larger cohorts and extended follow-up time to validate these initial findings. Continued monitoring of recipient survival as well as the incidence of device-associated complications remains an important task in the future.

Strengths and Limitations

Our work focuses exclusively on SHK recipients. Given that the heart allocation policy change took effect on October 18, 2018, the total number of patients with SHK in the current allocation era remains relatively low. Our survival analysis was limited to 1 y, and although unlikely given the upfront risk with tMCS use, survival curves may diverge when follow-up time is extended. Further analyses are planned in the future that include longer follow-up periods. Given the limitations of the SRTR source file, data from the pre–heart allocation change era were censored on October 1, 2018. It also lacks individual, granular data on pretransplant creatinine values, dialysis chronicity, the potential number of rehospitalizations within the first year after transplant, as well as complication rates specific to individual devices. Therefore, this information could not be included in our article. It is important to emphasize that the significant increase in tMCS use after the allocation policy change does not necessarily represent an increase in candidate disease severity but rather a change in clinical practice. Although support with a tMCS device may be beneficial to improve end-organ perfusion, associated complications are not negligible, and the risk–benefit ratio has to be individualized for each candidate. We expect a further increase in overall pre-SHK tMCS utilization, and updates to our initial analysis will be necessary.

CONCLUSION

We found a significant increase in pretransplant tMCS use in SHK candidates after the heart allocation policy update, particularly IABP. Despite this shift in management approach, 1-y posttransplant survival rates remained unchanged, suggesting that tMCS use is a safe strategy when implemented by an expert, multidisciplinary team. Seamless collaboration between the cardiology, renal transplant, and surgical teams is essential. Further studies with larger cohorts and longer-term outcomes data are required to confirm our findings.

ACKNOWLEDGMENTS

The data reported here have been supplied by the Hennepin Healthcare Research Institute as the contractor for the SRTR. The interpretation and reporting of these data are the responsibility of the authors and in no way should be seen as an official policy of or interpretation by the SRTR or the US Government.

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