Increasing heart transplant donor pool by liberalization of size matching

Impact of size matching on survival post-heart transplant in infants: Estimated total cardiac-volume ratio outperforms donor-recipient weight ratio

BACKGROUND

Cardiac volume-based estimation offers an alternative to donor-recipient weight ratio (DRWR) in pediatric heart transplantation (HT) but has not been correlated to posttransplant outcomes. We sought to determine whether estimated total cardiac volume (eTCV) ratio is associated with HT survival in infants.

METHODS

The United Network for Organ Sharing database was used to identify infants (aged <1 year) who received HT in 1987-2020. Donor and recipient eTCV were calculated from weight using previously published data. Patient cohort was divided acc ording to the significant range of eTCV ratio; characteristics and survival were compared.

RESULTS

A total of 2845 infants were identified. Hazard ratio with cubic spline showed prognostic relationship of eTCV ratio and DRWR with the overall survival. The cut point method determined an optimal eTCV ratio range predictive of infant survival was 1.05 to 1.85, whereas no range for DRWR was predictive. Overall, 75.6% of patients had an optimal total cardiac volume ratio, while 18.1% were in the lower (LR) and 6.3% in the higher (HR) group. Kaplan-Meier analysis showed better survival for patients within the optimal vs LR (p = 0.0017) and a similar significantly better survival when compared to HR (p = 0.0053). The optimal eTCV ratio group (n = 2,151) had DRWR, ranging from 1.09 to 5; 34.3% had DRWR of 2% to 3%, and 5.0% had DRWR of >3.

CONCLUSIONS

Currently, an upper DRWR limit has not been established in infants. Therefore, determining the optimal eTCV range is important to identify an upper limit that significantly predicts survival benefit. This finding suggests a potential increase in donor pool for infant recipients since over 40% of donors in the optimal eTCV range include DRWR values >2 that are traditionally not considered for candidate listing.

Utility of Recipient Cardiothoracic Ratio in Predicting Delayed Chest Closure after Heart Transplantation

BACKGROUND

 Predicted cardiac mass (PCM) has been well validated for size matching donor hearts to heart transplantation recipients. We hypothesized that cardiothoracic ratio (CTR) could be reflective of recipient-specific limits of oversizing, and sought to determine the utility of donor to recipient PCM ratio (PCMR) and CTR in predicting delayed chest closure after heart transplantation.

METHODS

 A retrospective review of prospectively collected data on 38 consecutive heart transplantations performed at our institution from 2017 to 2020 was performed. Donor and recipient PCM were estimated using Multi-Ethnic Study of Atherosclerosis predictive models. Receiver operating characteristic analysis was performed to determine the discriminatory power of the ratio of PCMR to CTR in predicting delayed sternal closure.

RESULTS

 Of the 38 patients, 71.1% (27/38) were male and the median age at transplantation was 58 (interquartile range [IQR]: 47-62) years. Ischemic cardiomyopathy was present in 31.6% of recipients (12/38). Median recipient CTR was 0.63 [IQR: 0.59-0.66]. Median donor to recipient PCMR was 1.07 [IQR: 0.96-1.19], which indicated 7% oversizing. Thirteen out of 38 (34.2%) underwent delayed sternal closure. Primary graft dysfunction occurred in 15.8% (6/38). PCMR/CTR showed good discriminatory power in predicting delayed sternal closure [area under the curve: 80.4% (65.3-95.6%)]. PCMR/CTR cut-off of 1.7 offered the best trade-off between the sensitivity (69.6%) and specificity (91.7%).

CONCLUSION

 CTR could be helpful in guiding the recipient-specific extent of oversizing donor hearts. Maintaining the ratio of PCMR to CTR below 1.7 could avoid excessive oversizing of the donor heart.

Deep Learning for Automated Measurement of Total Cardiac Volume for Heart Transplantation Size Matching

Total Cardiac Volume (TCV)-based size matching using Computed Tomography (CT) is a novel technique to compare donor and recipient heart size in pediatric heart transplant that may increase overall utilization of available grafts. TCV requires manual segmentation, which limits its widespread use due to time and specialized software and training needed for segmentation. This study aims to determine the accuracy of a Deep Learning (DL) approach using 3-dimensional Convolutional Neural Networks (3D-CNN) to calculate TCV, with the clinical aim of enabling fast and accurate TCV use at all transplant centers. Ground truth TCV was segmented on CT scans of subjects aged 0-30 years, identified retrospectively. Ground truth segmentation masks were used to train and test a custom 3D-CNN model consisting of a DenseNet architecture in combination with residual blocks of ResNet architecture. The model was trained on a cohort of 270 subjects and a validation cohort of 44 subjects (36 normal, 8 heart disease retained for model testing). The average Dice similarity coefficient of the validation cohort was 0.94 ± 0.03 (range 0.84-0.97). The mean absolute percent error of TCV estimation was 5.5%. There is no significant association between model accuracy and subject age, weight, or height. DL-TCV was on average more accurate for normal hearts than those listed for transplant (mean absolute percent error 4.5 ± 3.9 vs. 10.5 ± 8.5, p = 0.08). A deep learning-based 3D-CNN model can provide accurate automatic measurement of TCV from CT images. This initial study is limited as a single-center study, though future multicenter studies may enable generalizable and more accurate TCV measurement by inclusion of more diverse cardiac pathology and increasing the training data.

Deep Learning for Automated Measurement of Total Cardiac Volume for Heart Transplantation Size Matching

Background

Total Cardiac Volume (TCV) based size matching using Computed Tomography (CT) is a novel technique to compare donor and recipient heart size in pediatric heart transplant that may increase overall utilization of available grafts. TCV requires manual segmentation, which limits its widespread use due to time and specialized software and training needed for segmentation.

Objective

This study aims to determine the accuracy of a Deep Learning (DL) approach using 3-dimensional Convolutional Neural Networks (3D-CNN) to calculate TCV, with the clinical aim of enabling fast and accurate TCV use at all transplant centers.

Materials and Methods

Ground truth TCV was segmented on CT scans of subjects aged 0-30 years, identified retrospectively. Ground truth segmentation masks were used to train and test a custom 3D-CNN model consisting of a Dense-Net architecture in combination with residual blocks of ResNet architecture.

Results

The model was trained on a cohort of 270 subjects and a validation cohort of 44 subjects (36 normal, 8 heart disease retained for model testing). The average Dice similarity coefficient of the validation cohort was 0.94 ± 0.03 (range 0.84-0.97). The mean absolute percent error of TCV estimation was 5.5%. There is no significant association between model accuracy and subject age, weight, or height. DL-TCV was on average more accurate for normal hearts than those listed for transplant (mean absolute percent error 4.5 ± 3.9 vs. 10.5 ± 8.5, p = 0.08).

Conclusion

A deep learning based 3D-CNN model can provide accurate automatic measurement of TCV from CT images.

Is the practice of using oversized organs for recipients with elevated pulmonary vascular resistance justified?

OBJECTIVE

The purpose of this study was to assess post-transplantation outcomes in recipients with increased pulmonary vascular resistance (PVR) in relation to donor size.

METHODS

The United Network for Organ Sharing database was used to identify patients ages 0 to 18 years at time of listing who underwent transplantation from 2010 to 2019 and for whom cardiac catheterization and donor-recipient weight ratio data were available. Patients were divided according to listing PVR into <3, 3 to 6, and >6 Wood units. Donor-recipient weight ratio was categorized as undersized (≤0.80), midsize (0.81-1.2), and oversized (>1.2). Subgroup analysis was done with an additional supersized group (>2.0).

RESULTS

Fourteen hundred ninety-one patients met study criteria. Median age was 10 (interquartile range, 3-15) years and 45% were female. Four percent of heart transplantation cases used undersized, 45% used midsize, and 51% used oversized organs. More patients with PVR >6 were received an oversized organ transplant compared with patients with PVR <3; 59% (148/252) versus 48% (430/894); P = .003. There was no difference in survival among organ size groups regardless of PVR; this includes patients with PVR >6 at listing who received an oversized organ transplant versus an undersized (P = .359) or midsized (P = .956) organ. In subgroup analysis, even in patients who received a supersized organ transplant, there was no survival difference noted regardless of PVR.

CONCLUSIONS

Despite a persistent practice pattern to transplant oversized organs in high-PVR patients, there remains no difference in post-transplantation survival among these patients and those who received smaller organ transplants. Therefore, transplants in patients with high PVR should not be delayed by waiting for larger donors.

No Evidence for Oversizing Hearts and Donor Size Impact on 1-Year Survival in Heart Failure Patients With Left Ventricular Assist Device

The predicted heart mass (PHM) ratio has recently emerged as a better metric for donor-to-recipient size-matching than weight ratios. It is unknown whether this applies to transplant candidates on left ventricular assist device (LVAD) support. Our study examines if PHM ratio is optimal for size-matching specifically in the LVAD patient population. Patients with LVAD who received a heart transplant from January 1997 to December 2020 in the Scientific Registry of Transplant Recipients database were studied. We compared 5 size-matching metrics, including donor-recipient ratios of weight, height, body mass index, body surface area, and PHM. Single and multivariable Cox proportional hazards models for 1-year mortality were calculated. Our sample consisted of 11,891 patients. In our multivariate analysis, we found that patients in the undersized group with PHM ratios <0.83 had a hazard ratio for 1-year mortality of 1.34 (95% confidence interval 1.08 to 1.65, p = 0.007) suggestive of increased mortality with the use of undersized donors. There was no statistical difference in mortality between the matched (PHM ratio 0.83 to 1.2) and oversized group (PHM ratio ≥1.2). In heart transplant recipients on LVAD support, the PHM ratio provides better risk stratification than other metrics. Use of undersized donor hearts with PHM ratio <0.83 confers higher 1-year mortality. Using oversized donor hearts for transplantation in recipients on LVAD support has no benefit.

Donor/recipient ascending aortic diameter ratio as a novel potential metric for donor selection and improved clinical outcomes in heart transplantation: a propensity score-matched study

Background

Donor/recipient size matching is paramount in heart transplantation. Body weight, height, body mass index, body surface area, and predicted heart mass (PHM) ratios are generally used in size matching. Precise size matching is important to achieve better clinical outcomes. This study aims to determine the donor/recipient ascending aortic diameter (AAoD) ratio as a metric for donor selection and its effect on postoperative clinical outcomes in heart transplant patients.

Methods

We retrospectively reviewed all consecutive patients who underwent heart transplantation from January 2015 to December 2018. A cutoff value of 0.8032 for the donor/recipient AAoD ratio (independent variable for the primary endpoint during unmatched cohort analysis) was determined for predicting in-hospital mortality. The patients were divided into two groups based on the cutoff value. Group A, AAoD < 0.8032 (n = 96), and Group B, AAoD > 0.8032 (n = 265). A propensity score-matched (PSM) study was performed to equalize the two groups comprising 77 patients each in terms of risk. A Cox regression model was developed to identify the independent preoperative variables affecting the primary end-point. The primary endpoint was all-cause in-hospital mortality.

Results

A total of 361 patients underwent heart transplantation during the given period. On the multivariate analysis, donor/recipient PHM ratio [HR 16.907, 95% confidence interval (CI) 1.535-186.246, P = 0.021], donor/recipient AAoD ratio < 0.8032 (HR 5.398, 95% CI 1.181-24.681, P = 0.030), and diabetes (HR 3.138, 95% CI 1.017-9.689, P = 0.047) were found to be independent predictors of in-hospital mortality. Group A had higher 3-year mortality than Group B (P = 0.022). The surgery time was longer and postoperative RBC, plasma, and platelets transfusion were higher in Group A (P < 0.05). Although not statistically significant the use of continuous renal replacement therapy (P = 0.054), and extracorporeal membrane oxygenation (P = 0.086), was realatively higher, and ventilation time (P = 0.079) was relatively longer in Group A.

Conclusions

The donor/recipient AAoD ratio is a potential metric for patient matching and postoperative outcomes in heart transplantation. A donor/recipient AAoD ratio > 0.8032 could improve post-heart transplantation outcomes and donor heart utilization.

Choosing wisely: incorporating appropriate donor-recipient size matching in heart transplantation

Historically, transplantation of a female donor heart to male recipient has been viewed with caution given evidence of suboptimal outcomes, particularly in special populations such as patients with pulmonary hypertension or those supported by ventricular assist devices. However, the use of predicted heart mass ratio for donor-recipient size matching demonstrated that the size of the organ rather than sex of the donor was most responsible for the outcomes. With the advent of the predicted heart mass ratio, avoiding female donor hearts for male recipients is no longer justified and may result in unnecessary waste of available organs. In this review, we highlight the value of donor-recipient sizing by predicted heart mass ratio and summarize the evidence of different approaches to the donor-to-recipient size and sex matching. We conclude that the utilization of predicted heart mass is currently considered a preferred method of matching heart donors and recipients.

Donor-Recipient Weight Match in Pediatric Heart Transplantation: Liberalizing Weight Matching with Caution

(1) Background: To expand the donor pool, greater donor hearts tended to be used in heart transplantation. However, the data about the feasibility of expanding the donor and recipient weight ratios (DRWRs. All donor and recipient weight ratio (DRWR) in this study or cited from other articles were converted to the DRWR calculated by ((donor weight-recipient weight)/recipient weight) × 100%.) to >30% was still scant in China’s pediatric heart transplantation (HTx). The potential risk increased along with the further expansion of the appropriate range of DRWR to >30% and its upper limit was still in debate. (2) Methods: Seventy-eight pediatric patients (age < 18 years) undergoing HTx between 2015 and 2020 at our center were divided into two groups based on the DRWR (>30% and ≤30%). Variables were summarized and analyzed via univariate analyses and multivariate analyses. A Kaplan-Meier methodology was used to calculate survival and conditional survival. (3) Results: No significant difference was found in one-year, three-year or five-year survival between the two groups. (4) Conclusions: The expansion of DRWR to >30% was acceptable for China’s pediatric HTx. Notably, continuously liberalizing of the upper DRWR boundary to more than 200% could be used as a stop-loss option but should be applied with caution.

Cardiac Surgery in Advanced Heart Failure

Mechanical circulatory support and heart transplantation are established surgical options for treatment of advanced heart failure. Since the prevalence of advanced heart failure is progressively increasing, there is a clear need to treat more patients with mechanical circulatory support and to increase the number of heart transplantations. This narrative review summarizes recent progress in surgical treatment options of advanced heart failure and proposes an algorithm for treatment of the advanced heart failure patient at >65 years of age.

Impact of Obesity on Heart Transplantation Outcomes

Background

Patients with obesity and advanced heart failure face unique challenges on the path to heart transplantation. There are limited data on waitlist and transplantation outcomes in this population. We aimed to evaluate the impact of obesity on heart transplantation outcomes, and to investigate the effects of the new organ procurement and transplantation network allocation system in this population.

Methods and Results

This cohort study of adult patients listed for heart transplant used the United Network for Organ Sharing database from January 2006 to June 2020. Patients were stratified by body mass index (BMI) (18.5–24.9, 25–29.9, 30–34.9, 35–39.9, and 40–55 kg/m²). Recipient characteristics and donor characteristics were analyzed. Outcomes analyzed included transplantation, waitlist death, and posttransplant death. BMI 18.5 to 24.9 kg/m² was used as the reference compared with progressive BMI categories. There were 46 645 patients listed for transplantation. Patients in higher BMI categories were less likely to be transplanted. The lowest likelihood of transplantation was in the highest BMI category, 40 to 55 kg/m² (hazard ratio [HR], 0.19 [0.05–0.76]; P=0.02). Patients within the 2 highest BMI categories had higher risk of posttransplantation death (HR, 1.29; P<0.001 and HR, 1.65; P<0.001, respectively). Left ventricular assist devices among patients in obese BMI categories decreased after the allocation system change (P<0.001, all). After the change, patients with obesity were more likely to undergo transplantation (BMI 30–35 kg/m²: HR, 1.31 [1.18–1.46], P<0.001; BMI 35–55 kg/m²: HR, 1.29 [1.06–1.58]; P=0.01).

Conclusions

There was an inverse relationship between BMI and likelihood of heart transplantation. Higher BMI was associated with increased risk of posttransplant mortality. Patients with obesity were more likely to undergo transplantation under the revised allocation system.

Innovations in Heart Transplantation: A Review

Advanced heart failure affects tens of thousands of people in the United States alone with high morbidity and mortality. Cardiac transplantation offers the best treatment strategy but has been historically limited by donor availability. Recently, there have been significant advances in organ allocation, donor-recipient matching, organ preservation and expansion of the donor pool. The current heart allocation system prioritizes the sickest patients to minimize waitlist mortality. Advances in donor organ selection including predicted heart mass calculations and more sophisticated antibody detection methods for allosensitized patients offer more effective matching of donors and recipients. Innovations in organ preservation such as with organ preservation systems have geographically widened the donor pool. The use of hepatitis C donors is possible with the advent of effective direct-acting antiviral agents to cure donor-transmitted hepatitis C. Finally, further expansion of the donor pool is occurring with the utilization of higher-risk donors with advanced age, medical comorbidities, and left ventricular dysfunction and advances in donation after circulatory death. This review provides an update on the new technologies and transplantation strategies that serve to widen the donor pool and more effectively match donors and recipients so that heart transplant candidates may derive the best outcomes from heart transplantation.

Current Status of and Opinions on Heart Transplantation in China

The purpose of this review is to provide a comprehensive update on recent advances in heart transplantation in China. Despite advances in pharmacologic and device treatment of chronic heart failure, long-term morbidity and mortality remain high, and many patients progress to endstage heart failure. Heart transplantation has become standard treatment for selected patients with end-stage heart failure, though challenges still exist. However, multiple advances over the past few years will improve the survival and quality-of-life of heart transplant recipients. This article elaborates on the specific characteristics of heart transplantation in China, the current issues, development trends, and related experiences with heart transplantation in Wuhan Union Hospital.

Pediatric urgent heart transplantation with age or weight mismatched donors: Reducing waiting time by enlarging donor criteria

BACKGROUND

Despite considerable progress in heart transplantation, pediatric waiting list mortality is still high, and often patients do not have enough time to wait. We hypothesized that extending the donor criteria regarding age and weight mismatch does not significantly affect the early follow-up.

METHODS

We retrospectively analyzed our pediatric heart transplantation patients operated on from 2014 to 2020 for high (>3.0) or low (<0.6) donor-recipient weight ratio (DRWR) or chronological age mismatches (donor organ >5 years older than recipient age). This patient cohort constituted "mismatched heart transplantations" (mHTX). We compared mHTX preoperative status, postoperative course, 1-year survival, and early clinical follow-up to standard pediatric heart transplantations (sHTX).

RESULTS

We performed 20 pediatric heart transplantations-10 mHTX and 10 sHTX. The minimum DRWR was 0.44, the maximum was 5.60, and the maximum age mismatch was 42.6 years. Median days in the intensive care unit (p = .436) and time-to-first-rejection episode (p = .925) were comparable. Nine patients in each group were alive after 1 year, two patients were operated within 1 year of follow-up. One mHTX patient developed cardiac allograft vasculopathy after 15 months and died 648 days after transplantation (p = .237). All other patients were alive at the end of follow-up and in good clinical conditions (median follow-up for mHTX was 732.5 days, 1149.5 days for sHTX).

CONCLUSION

Postoperative course and early follow-up after mHTX were comparable to sHTX. In urgent clinical situations, extended donor criteria may be considered an additional option for pediatric heart transplantation.

Improving the metrics for donor heart sizing

Predicted heart mass matches donor and recipient sizing for heart transplantation. Physiologic considerations further refines matching and can allow for safe use of undersized and sex mismatched organs.

Reducing the wait: TCV can expand the donor pool for heart transplant candidates

A 16-year-old with new-onset dilated cardiomyopathy underwent VAD placement, later complicated by low flow from outflow graft kinking. To expedite heart transplantation, TCV was calculated and compared with 141 normal patients pinpointing the upper weight threshold. He was transplanted 2 days later within the expanded weight range with no post-transplant complications.

Donor and Recipient Size Matching in Heart Transplantation With Predicted Heart and Lean Body Mass

Donor and recipient size matching during heart transplant can be assessed using weight or predicted heart mass (PHM) ratios. We developed sex-specific allomteric equations for PHM and predicted lean body mass (PLBM) using the United Kingdom Biobank (UKB) and evaluated their predictive value in the United Network of Organ Sharing database. Donor and recipient size matching was based on weight, PHM and PLBM ratios. PHM was calculated using the Multiethnic Study of Atherosclerosis and UKB equations. PLBM was calculated using the UKB and National Health and Nutrition Examination Survey equations. Relative prognostic utility was compared using multivariable Cox analysis, adjusted for predictors of 1-year survival in the Scientific Registry of Transplant Recipients model. Of 53,648 adult patients in the United Network of Organ Sharing database between 1996 and 2016, 6528 (12.2%) died within the first year. In multivariable analysis, undersized matches by any metric were associated with increased 1-year mortality (all P < 0.01). Oversized matches were at increased risk using PHM or PLBM (all P < 0.01), but not weight ratio. There were significant differences in classification of size matching by weight or PHM in sex-mismatched donor-recipient pairs. A significant interaction was observed between pulmonary hypertension and donor undersizing (hazard ratio 1.15, P = 0.026) suggesting increased risk of undersizing in pulmonary hypertension. Donor and recipient size matching with simplified PHM and PLBM offered an advantage over total body weight and may be more important for sex-mismatched donor-recipient pairs. Donor undersizing is associated with worse outcomes in patients with pulmonary hypertension.

The Year in Cardiothoracic Transplantation Anesthesia: Selected Highlights from 2019

The highlights in cardiothoracic transplantation focus on the recent research pertaining to heart and lung transplantation, including expansion of the donor pool, the optimization of donors and recipients, the use of mechanical support, the perioperative and long-term outcomes in these patient populations, and the use of transthoracic echocardiography to diagnose rejection.