Heart Transplant Waiting List Mortality　― Impact of HeartMate 3 and the Need for Prioritized Organ Allocation ―

Abstract

Background: Japan’s heart transplantation system is characterized by an extremely long waiting period, which contributes to significant mortality on the waiting list. The current allocation system may maintain favorable post-transplant outcomes at the expense of high-risk patients, particularly those with severe heart failure or complications following left ventricular assist device (LVAD) implantation. To explore an optimal allocation system for Japan, we investigated risk factors for waiting list mortality.

Methods and Results: We analyzed 300 patients registered on the heart transplant waiting list at Osaka University between 2014 and 2024. Cox hazard analysis identified age at registration (hazard ratio [HR] 1.023) and congenital heart disease (HR 4.531) as independent risk factors for mortality. In the LVAD cohort (n=244), right heart failure (HR 4.582), stroke associated with systemic infection (HR 5.175), and sudden stroke without preceding infection (HR 3.158) were significant risk factors. Although the HeartMate 3 significantly reduced sudden stroke (P<0.001), it did not improve right heart failure or infection-related stroke. Patients with these complications had significantly lower proportions of time at home with an LVAD (P<0.001).

Conclusions: Prioritized organ allocation for patients with congenital heart disease, right heart failure, or LVAD-related infections may improve waiting list survival. Reducing hospitalizations in high-risk LVAD patients could also be beneficial from a healthcare economics perspective.

The shortage of organ donors remains a global challenge, particularly in Japan, where the number of brain-dead organ donors is significantly lower than the number of patients awaiting transplantation.¹ Consequently, most heart transplant candidates in Japan require circulatory support with a left ventricular assist device (LVAD) and face an average waiting period of >5 years.^1,2 Since the revision of the Organ Transplant Law in July 2010, the number of heart transplants in Japan has gradually increased, surpassing 100 per year for the first time in 2023.³

Against this backdrop, there is growing momentum to improve the existing heart transplant allocation system to better serve critically ill patients who cannot be adequately supported under current policies. The Heart Transplant Society and other stakeholders are currently discussing the development of a revised allocation framework that prioritizes more severely ill patients by classifying them as Status 1A or 1B, thereby granting them preferential organ allocation.³ An optimal allocation system should aim to achieve both the lowest possible mortality among waitlisted patients and the best post-transplant outcomes. However, the current Japanese heart transplant allocation system appears to prioritize improving post-transplant outcomes, potentially at the expense of reducing waitlist mortality. In this study we analyzed risk factors associated with mortality among patients on the heart transplant waiting list, with the goal of informing the development of a more effective allocation system that minimizes waitlist mortality while maintaining favorable post-transplant outcomes in Japan.

Methods

Ethics Statement

This retrospective study was approved by the Institutional Review Board of Osaka University Graduate School of Medicine (Approval no. 21372(T1)-3, April 23, 2024). The requirement for written informed consent from participants was waived due to the anonymous nature of the data collected.

Patients

From the establishment of the heart transplant waiting list by the Japan Organ Transplant Network in 1997 up to December 2024, 528 patients in total were registered at Osaka University as their transplant facility. Among these patients, 331 were registered between January 2014 and December 2024. After excluding 15 patients who subsequently transferred to another transplant center, 2 patients who were deregistered for non-medical reasons, and 14 patients who had never undergone clinical evaluation at our hospital and for whom comprehensive clinical data were unavailable, 300 patients were included in this analysis.

Patient data were extracted from medical records stored in the hospital database. The primary endpoint was death after registration on the heart transplant waiting list. Follow-up was censored at the time of heart transplantation. A risk analysis of mortality while on the waiting list was conducted based on patient demographics and factors related to post-registration management.

Statistical Analysis

Continuous variables are presented as the mean±SD, whereas categorical variables are presented as numbers and proportions. All continuous variables were checked for normal distribution using the Shapiro-Wilk test and a normal probability plot. For univariate analysis, normally distributed variables were compared using Student’s t-tests, whereas non-normally distributed variables were compared using the Mann-Whitney U test. Categorical variables were compared using Chi-squared analysis or Fisher’s exact test, as appropriate. Patient survival on the transplant waitlist was analyzed using Kaplan-Meier estimates. Predictors of mortality were evaluated using the Cox hazard model. Factors with a value of P<0.10 in the univariate analysis were included in the multivariate analysis.

In all cases, 2-sided P<0.05 was considered to be statistically significant.

All statistical analyses were performed using EZR (Saitama Medical Center, Jichi Medical University, Saitama, Japan), a graphical user interface for R (R Foundation for Statistical Computing, Vienna, Austria). More precisely, EZR is a modified version of R commander designed to add statistical functions frequently used in biostatistics.⁴

Results

Patient Characteristics

Table 1 summarizes the characteristics of the 300 patients included in this study. The cohort consisted of 62% men and 38% women, with a mean age at registration of 36.9±20.6 years. Under the Japanese organ transplant allocation system, organs from donors aged <18 years are preferentially allocated to recipients who were aged <18 years at the time of registration; in our cohort, 72 (24%) patients were aged <18 years at the time of registration.

Table 1.

Patient Characteristics

	Total cohort (n=300)	LVAD cohort (n=244)	Non-LVAD cohort (n=56)
Female sex	114 (38.0)	91 (37.3)	23 (41.1)
Age at registration (years)	36.9±20.6	38.6±20.0	29.3 ±21.6
Age <18 years at registration	72 (24.0)	49 (20.1)	23 (41.1)
Etiology
Idiopathic dilated cardiomyopathy	156 (52.0)	134 (54.9)	22 (39.3)
Hypertrophic cardiomyopathy	33 (11.0)	30 (12.3)	3 (5.4)
Ischemic cardiomyopathy	31 (10.3)	29 (11.9)	2 (3.6)
Restrictive cardiomyopathy	16 (5.3)	3 (1.2)	13 (23.2)
Congenital heart disease	9 (3.0)	6 (2.5)	3 (5.4)
Others	55 (18.3)	42 (17.2)	13 (23.2)
Status 1 at registration	225 (75.0)	199 (81.6)	26 (46.4)
LVAD support during waiting period	244 (81.3)	244 (100)	0 (0)
Initial LVAD models
HeartMate 3		69 (28.3)
HeartMate II		64 (26.2)
EXCOR® pediatric		35 (14.3)
Jarvik2000		28 (11.5)
HVAD		21 (8.6)
EVAHEART		20 (8.2)
DuraHeart		7 (2.9)
LVAD comorbidities
LVAD pump exchange		39 (16.0)
Surgical intervention to aortic valveA		27 (11.1)
Right heart failureB		17 (7.0)
Driveline infection		63 (25.8)
Pump infection/mediastinitis		25 (10.3)
Stroke preceded by systemic infection		10 (4.1)
Stroke without preceding systemic infection		45 (18.4)

Unless indicated otherwise, data are given as the mean±SD or n (%). ^AIncluding surgical intervention at the time of LVAD implantation. ^BRequiring continuous inotrope support or mechanical right heart support. LVAD, left ventricular assist device.

The most common underlying condition was idiopathic dilated cardiomyopathy (52.0%), followed by hypertrophic cardiomyopathy or its dilated phase (11.0%), ischemic cardiomyopathy (10.3%), restrictive cardiomyopathy (5.3%), and congenital heart disease (3.0%). Other cardiomyopathies, including post-myocarditis cardiomyopathy, peripartum cardiomyopathy, valvular cardiomyopathy, and other secondary cardiomyopathies, were collectively present in 18.3% of patients.

At registration, 75.0% of patients required continuous inotropic support or mechanical circulatory assistance (Status 1), whereas 25.0% did not require such support (Status 2). Over the entire waiting period, 81.3% of patients required LVAD support at least once, whereas 18.7% did not.

Survival Rates After Registration

Figure 1 illustrates survival outcomes following heart transplant listing, with transplantation as a censoring event. The 1-, 3-, and 5-year survival rates were 92.8%, 86.4%, and 79.8%, respectively.

Figure 1.

Kaplan-Meier survival curve for 300 patients after registration on the Japan Organ Transplantation Network heart transplant waiting list, with transplantation treated as a censoring event.

Analysis of the Risk of Death While on the Waiting List

Table 2 presents the results of a multivariate analysis using the Cox hazard model to assess risk factors for mortality among patients on the heart transplant waiting list (n=300). Age at registration (hazard ratio [HR] 1.023) and congenital heart disease (HR 4.531) were identified as independent risk factors for mortality while on the waiting list. In contrast, registration at age <18 years, sex, status at registration, presence of LVAD support during the waiting period, and ischemic heart disease as the underlying etiology were not significant risk factors for mortality.

Table 2.

Risk of Death on the Waiting List (Total Cohort, n=300; Cox Hazard Model)

	Univariate	Multivariate
	P value	Hazard ratio	95% CI	P value
Age at registration	0.017	1.023	1.006–1.040	0.008
Age <18 years at registration	0.174
Sex	0.610
Status 1 at registration	0.415
Left ventricular assist device	0.152
Ischemic cardiomyopathy	0.713
Congenital heart disease	0.067	4.531	1.339–15.33	0.015

CI, confidence interval.

Outcomes in Patients With Congenital Heart Disease

Table 3 summarizes the characteristics and outcomes of 9 patients with congenital heart disease. The primary diseases varied widely, with 5 patients having single ventricle disease and 4 having biventricular disease. Three of these patients had adult congenital heart disease (ACHD). Six patients received LVAD support; 4 with an EXCOR Pediatric, 1 with the Jarvik2000, and 1 with the HeartMate 3. Of the 9 patients with congenital heart disease, 3 died (1 each due to stroke, lethal arrhythmia, and multiple organ failure), 3 successfully underwent heart transplantation, and the remaining 3 are still waiting for heart transplantation on LVAD support. Two of the 3 patients who died on the waiting list had ACHD.

Table 3.

Summary of Congenital Heart Disease Patients

Patient no.	Sex	AgeA (years)	Diagnosis	Previous surgery	LVAD	Duration of LVAD (days)	Time on waiting list (days)	Outcome	Cause of death
1	F	41	TGA (S, L, L), VSD, PS	VSD closure, RVOTR	Jarvik2000	1,389	1,379	Death	Cerebrovascular disease
2	M	26	PA/IVS	EC-TCPC	None	–	1,353	Death	Lethal arrhythmia
3	M	3	DILV, TGA	BDG+DKS procedures	Excor	1	463	Death	Multiple organ failure
4	F	39	VSD, PLSVC	VSD closure	None	–	1,487	HTx	–
5	F	3	AS, MS, CoA, hypo LV	EC-TCPC	Excor	465	488	HTx	–
6	F	14	TGA, VSD, PA	Rastelli	None	–	465	HTx	–
7	M	3	Asplenia, uAVSD, hypo LV	EC-TCPC	Excor	724 (ongoing)	711 (ongoing)	Waiting	–
8	F	3	Truncus (A2)	Palliative RVOTR	Excor	632 (ongoing)	589 (ongoing)	Waiting	–
9	F	12	DORV, PA	ICR	HeartMate 3	489 (ongoing)	479 (ongoing)	Waiting	–

^AAge at registration. AS, aortic stenosis; BDG, bidirectional Glenn; CoA, coarctation of the aorta; DILV, double-inlet left ventricle; DKS, Damus-Kaye-Stansel; DORV, double-outlet right ventricle; EC-TCPC, extracardiac total cavopulmonary connection; F, female; HTx, heart transplantation; hypo LV, hypoplastic left ventricle; LVAD, left ventricular assist device; M, male; MS, mitral stenosis; PA, pulmonary atresia; PA/IVS, pulmonary atresia with intact ventricular septum; PLSVC, persistent left superior vena cava; PS, pulmonary stenosis; RVOTR, right ventricular outflow tract reconstruction; TGA, transposition of great arteries; uAVSD, unbalanced atrioventricular septal defect; VSD, ventricular septal defect.

Outcomes in Patients Requiring LVAD Support

Table 1 presents the clinical characteristics of patients who required LVAD support while awaiting transplantation (n=244). The overall patient profile was similar to that of the entire cohort; however, restrictive cardiomyopathy was relatively uncommon, present in only 1.2% of patients. The initial LVAD device used was most frequently the HeartMate 3 (69 patients; 28.3%), followed by the HeartMate II (64 patients; 26.2%), EXCOR Pediatric (35 patients; 14.3%), Jarvik 2000 (28 patients; 11.5%), HVAD (21 patients; 8.6%), EVAHEART (20 patients; 8.2%), and DuraHeart (7 patients; 2.9%).

Several factors potentially influencing prognosis during LVAD support were identified. LVAD pump exchange was required in 39 (16.0%) patients, and surgical intervention for aortic valve insufficiency, including procedures performed at the time of LVAD implantation, was necessary in 27 (11.1%) patients. LVAD-related complications included right heart failure requiring continuous inotrope infusion or mechanical right heart support in 17 (7.0%) patients, driveline infection in 63 (25.8%) patients, and pump infection or mediastinitis in 25 (10.3%) patients. Stroke preceded by systemic infection occurred in 10 (4.1%) patients, whereas sudden stroke without preceding systemic infection was observed in 45 (18.4%) patients.

Table 4 summarizes the results of a multivariate analysis using the Cox hazard model to identify risk factors for mortality while on the waiting list among LVAD-supported patients (n=244). Independent risk factors for mortality included right heart failure requiring continuous inotrope infusion or mechanical right heart support (HR 4.582), stroke associated with systemic infection (HR 5.175), and sudden stroke without preceding systemic infection (HR 3.158). In contrast, LVAD type (e.g., extracorporeal LVAD or HeartMate 3), LVAD pump exchange, surgical intervention for the aortic valve, driveline infection, and pump infection or mediastinitis were not significant predictors of mortality while awaiting transplantation.

Table 4.

Risk of Death on the Waiting List (LVAD Cohort, n=244; Cox Hazard Model)

	Univariate	Multivariate
	P value	Hazard ratio	95% CI	P value
Extracorporeal LVAD	0.139
HeartMate 3 LVAD	0.013	0.430	0.123–1.484	0.182
LVAD pump exchange	0.385
Surgical intervention to aortic valve	0.015	1.372	0.648–2.907	0.409
Right heart failure	<0.001	4.582	2.086–10.070	<0.001
Driveline infection	0.197
Pump infection/mediastinitis	0.038	1.369	0.486–3.859	0.553
Stroke preceded by systemic infection	<0.001	5.175	1.594–16.800	0.006
Stroke without preceding systemic infection	<0.001	3.158	1.582–6.307	0.001

Abbreviations as in Tables 1,2.

Impact of HeartMate 3 on Mortality Risk Factors

In a multivariate analysis using the Cox hazard model, the use of the HeartMate 3 was not identified as an independent risk factor for mortality while on the waiting list. However, overall outcomes for LVAD-supported patients have markedly improved since the introduction of the HeartMate 3 (Figure 2).

Figure 2.

Kaplan-Meier survival curves comparing patients supported with the HeartMate 3 with those supported by other left ventricular assist devices (LVADs) after registration on the heart transplant list.

To explore the reasons behind this improvement, we examined the association between the HeartMate 3 and the 3 independent risk factors for mortality on the waiting list: right heart failure, stroke associated with systemic infection, and sudden stroke without preceding systemic infection (Figure 3). The incidence of right heart failure and stroke associated with systemic infection did not differ significantly between the HeartMate 3 and other LVADs. However, the occurrence of sudden stroke without preceding systemic infection was significantly lower in patients supported with the HeartMate 3 compared with those with other LVADs (P<0.001).

Figure 3.

Incidence of left ventricular assist device (LVAD)-related complications, namely right heart failure, stroke associated with systemic infection, and stroke without preceding infection, in patients with supported with the HeartMate 3 and those supported with other LVADs.

Waiting List Mortality Risk and Duration of Home LVAD Support

Two major risk factors for mortality while on the transplant waiting list, namely right heart failure and stroke associated with systemic infection (or systemic infection related to LVAD support), were not significantly improved by the introduction of the HeartMate 3. Both these conditions are also well-established risk factors for hospital readmission following LVAD implantation.

To assess the impact of these risk factors on the duration of home-based LVAD support, we analyzed the proportion of time patients spent at home after LVAD implantation (Figure 4). Patients who developed right heart failure had a significantly lower proportion of time spent at home than those without right heart failure (P<0.001). Similarly, patients who experienced stroke associated with systemic infection spent significantly less time at home than those without this complication (P=0.042). In addition, patients who died while awaiting heart transplantation had a significantly lower proportion of time at home after LVAD implantation than those who ultimately underwent transplantation (P<0.001).

Figure 4.

Proportion of time spent at home after left ventricular assist device (LVAD) implantation for patients with vs. without right heart failure (RHF; Left), patients with vs. without stroke associated with systemic infection (Middle), and patients who underwent heart transplantation (HTx) vs. those who died while on the waiting list (Right). Data are the mean±SD.

Discussion

Japan’s heart transplant allocation system has played a crucial role in maintaining strict impartiality, particularly in a country where brain-dead organ transplantation has faced significant opposition since its inception. Today, 25 years after the introduction of brain-dead organ transplantation, concerns about the “unfairness” of the system itself are rarely raised. The prolonged waiting period under this allocation framework inherently favors patients who “survive” the waiting period, thereby ensuring that only the most resilient candidates receive a heart transplant. This has contributed to Japan’s consistently excellent post-transplant outcomes, which surpass global standards.¹

However, a major issue with the Japanese heart transplant system remains the exceptionally long waiting period, with an average wait time >5 years for patients listed under Status 1.¹ In reality, survival rates on the transplant waiting list are lower than post-transplant survival rates (Figure 1). It is not an exaggeration to state that Japan’s favorable post-transplant outcomes come at the cost of high waiting-list mortality.

The key findings of the present study are listed below.

• Age at registration and congenital heart disease are significant risk factors for mortality while on the waiting list.

• Right heart failure and stroke following LVAD implantation are major risk factors for mortality during the waiting period.

• The introduction of the HeartMate 3 has significantly reduced the incidence of sudden stroke without preceding systemic infection. However, it has not mitigated the risks of right heart failure or stroke associated with systemic infection.

• Patients with right heart failure or stroke associated with systemic infection experience significantly longer hospital stays as a proportion of their total LVAD-supported period. In addition, patients who died while on the waiting list had a significantly higher proportion of their LVAD-supported time spent in the hospital than those who successfully underwent heart transplantation.

These findings suggest that prioritizing heart transplantation for patients with congenital heart disease and those experiencing right heart failure or systemic infection after LVAD implantation may improve overall waiting list survival. Furthermore, reducing hospital stays following LVAD implantation may have substantial benefits from a healthcare economics perspective.

It is well established that age is a critical factor influencing outcomes in the treatment of severe heart failure, as demonstrated in our previous risk analysis of LVAD therapy.⁵ The latest Japanese Registry for Mechanically Assisted Circulatory Support (J-MACS) statistical report also confirms that older age is associated with lower survival rates following LVAD implantation (log-rank P<0.001).^6,7

The high mortality rate observed in patients with congenital heart disease while on the transplant waiting list is consistent with previous studies. Mital et al. analyzed 46 patients aged <20 years who were listed for heart transplantation due to heart failure secondary to congenital heart disease and reported a 29% mortality rate while awaiting transplantation.⁸ The mortality rate was particularly striking among infants, reaching 71%, in stark contrast to infants with cardiomyopathy, all of whom were successfully bridged to transplantation.⁸ Despite these challenges, heart transplantation remains an effective treatment for end-stage heart failure due to congenital heart disease, although the likelihood of reaching transplantation is lower than that for patients with cardiomyopathy-related heart failure.^9,10 Of the 9 patients with congenital heart disease in our cohort, 3 had ACHD, 2 of whom died while on the waiting list (Table 3). This may also have contributed to the result that age at registration was the risk factor for death on the waiting list.

Although prioritizing heart transplantation for patients with congenital heart disease may reduce mortality while on the waiting list, we also need to consider its effects on survival after heart transplantation. Many factors contribute to early mortality after heart transplantation in patients with congenital heart disease, including failing Fontan pathophysiology, prolonged ischemia time due to the complex anatomy, increased pulmonary pressure, and older recipient age.¹¹ Nevertheless, many studies found a similarly good or even better long-term survival when patients survived the early stage.^12,13

Severe biventricular heart failure requiring continuous inotrope support or mechanical right heart support following LVAD implantation is a well-recognized risk factor for mortality after LVAD placement.^5,14,15 In a previous study, we conducted a simulation to estimate post-LVAD survival in heart transplant candidates at Osaka University under the hypothetical scenario that patients with severe biventricular failure could receive a heart transplant within approximately 1 year. The results suggested that the life expectancy of patients with biventricular failure would become comparable to that of patients with LVAD support alone, highlighting the potential benefit of prioritizing organ allocation for LVAD patients with severe right heart failure.¹⁶ Conversely, there are some previous reports indicating that patients who develop late-onset right heart failure during LVAD support have significantly worse 5-year post-transplant survival rates compared with those without right heart failure (26% vs. 87%; P<0.0001).¹⁷ King et al. reported that patients who developed right heart failure after LVAD implantation had a significantly increased risk of primary graft dysfunction following transplantation.¹⁸ The precise mechanisms by which pretransplant right heart failure influences post-transplant outcomes remain unclear and warrant further investigation.

In 2018, the United Network for Organ Sharing in the US revised its heart transplant allocation system to reduce mortality on the waiting list, transitioning from the previous 3-tiered system (Status 1A, 1B, and 2) to a 6-tiered priority system (Status 1–6).¹⁹ Under this system, the highest priority, Status 1, is assigned to patients requiring extracorporeal membrane oxygenation support, whereas patients with single-ventricle physiology requiring total artificial heart or ventricular assist device are classified as Status 2. Patients with other congenital heart diseases are generally categorized as Status 4. This revision has led to a shorter waiting period and an increased likelihood of transplantation for patients with congenital heart disease, without significantly affecting post-transplant mortality.²⁰ Although we also propose prioritization of heart transplantation for patients with congenital heart disease in Japan, congenital heart disease includes various type of etiologies, physiologies, and pathologies, and how to select urgent candidates among these patients is another important consideration.

The new allocation system in the US also classifies patients with an implantable LVAD who cannot be discharged as Status 2, granting them higher priority. Notably, patients with right heart failure requiring inotrope or mechanical right heart support, as well as those with LVAD-related infections at risk of stroke, two significant risk factors for mortality on the waiting list identified in our study, fall into this high-priority category.

Following the implementation of this revised allocation system in the US, studies have reported a reduction in transplant waiting times^21–23 and an improvement in waiting list survival rates.^24,25 Although the impact of this change on post-transplant outcomes has been examined in many studies, most findings indicate that post-transplant survival has remained unchanged.^21,22,26,27

Study Limitations

This study has several limitations. First, it was a single-center, retrospective analysis, which may limit the generalizability of the findings to other institutions or healthcare systems. Differences in patient management, selection criteria, and post-LVAD care across centers could influence outcomes.

Second, although we identified significant risk factors for mortality while on the heart transplant waiting list, unmeasured confounders may have influenced our results. Factors such as socioeconomic status, caregiver support, and patient adherence to medical management were not analyzed but could affect survival.

Third, although we demonstrated that the introduction of the HeartMate 3 was associated with improved LVAD outcomes, this study did not directly assess long-term complications or quality of life in patients supported by different types of LVADs. Further investigations with longer follow-up and comprehensive functional assessments are needed.

Fourth, the number of patients with congenital heart disease in our cohort was relatively small, which may have limited the statistical power to detect additional risk factors specific to this population. Larger multicenter studies are necessary to validate our findings in this subgroup.

Finally, the impact of our findings on healthcare policy and organ allocation remains speculative. Although we suggest that prioritizing heart transplantation for high-risk LVAD patients could reduce waiting list mortality and hospitalization burden, prospective studies or simulation models are needed to assess the feasibility and ethical implications of such an approach.

Conclusions

Age at heart transplant registration, congenital heart disease, right heart failure after LVAD implantation, and stroke due to LVAD-related infection were significant risk factors for mortality while on the heart transplant waiting list. Although the introduction of the HeartMate 3 has improved LVAD outcomes, it has not significantly mitigated these specific mortality risks. Prioritizing organ allocation for patients with these risk factors may be an effective strategy to improve survival rates on the waiting list. In addition, right heart failure and LVAD-related infections are major contributors to prolonged hospitalization after LVAD implantation. Prioritizing heart transplantation for these patients may help reduce hospitalization duration and offer economic benefits in terms of healthcare resource utilization.

Acknowledgments

None.

Sources of Funding

This research received no grants from any funding agency in the public, commercial, or non-profit sectors.

Disclosures

The authors declare no conflicts of interest.

IRB Information

This study was approved by the Institutional Review Board of Osaka University Graduate School of Medicine (Approval no. 21372(T1)-3, April 23, 2024).

Data Availability

The deidentified participant data will not be shared.

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