Volumetrics and fit assessments for donor to recipient size matching in pediatric heart transplantation: Is it time for a new paradigm?

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.

Echocardiography Provides a Reliable Estimate of Total Cardiac Volume for Pediatric Heart Transplantation

BACKGROUND

Donor-to-recipient size matching for heart transplantation typically involves comparing donor and recipient body weight; however, weight is not linearly related to cardiac size. Attention has shifted toward the use of computed tomography- (CT-) derived total cardiac volume (TCV), that is, CT-TCV, to compare donor and recipient heart organ size. At this time, TCV size matching is near impossible for most centers due to logistical limitations. To overcome this impediment, echocardiogram-derived TCV (ECHO-TCV) is an attractive, alternative option to estimate CT-TCV. The goal of this study is to test whether ECHO-TCV is an accurate and reliable surrogate for TCV measurement compared with the gold standard CT-TCV.

METHODS

ECHO-TCV and CT-TCV were measured in a cohort spanning the neonatal to young adult age range with the intention to simulate the pediatric heart transplant donor pool. ECHO-TCV was measured using a modified Simpson's summation-of-discs method from the apical 4-chamber (A4C) view. The gold standard of CT-TCV was measured from CT scans using three-dimensional reconstruction software. The relationship between ECHO-TCV and CT-TCV was evaluated and compared with other anthropometric and image-based markers that may predict CT-TCV. Inter-rater reliability of ECHO-TCV was tested among 4 independent observers. Subanalyses were performed to identify imaging views and timing that enable greater accuracy of ECHO-TCV.

RESULTS

Banked imaging data of 136 subjects with both echocardiogram and CT were identified. ECHO-TCV demonstrated a linear relationship to CT-TCV with a Pearson correlation coefficient of r = 0.96 (95% CI, 0.95-0.97; P < .0001) and mean absolute percent error of 8.6%. ECHO-TCV correlated most strongly with CT-TCV in the subset of subjects <4 years of age (n = 33; r = 0.98; 95% CI, 0.96-0.99; P < .0001). The single-score intraclass correlation coefficient across all 4 raters is 0.96 (interquartile range, 0.93-0.98). ECHO-TCV measured from a standard A4C view at end diastole with the atria in the plane of view had the strongest correlation to CT-TCV.

CONCLUSIONS

ECHO-TCV by the A4C view was found to be both an accurate and reliable alternative measurement of CT-TCV and is derived from readily available donor ECHO images. The ECHO-TCV findings in this study make the ECHO method an attractive means of direct donor-to-recipient TCV size matching in pediatric heart transplantation.

Evaluating predicted heart mass in adolescent heart transplantation

BACKGROUND

Predicted Heart Mass (PHM) has emerged as an attractive size matching metric in adult cardiac transplantation. However, since PHM was derived from a healthy adult cohort, its generalizability to the pediatric population is unclear. We hypothesize that PHM can be extended to older adolescents, and potentially broaden the donor pool available to this group.

METHODS

The United Network for Organ Sharing database was retrospectively analyzed for patients aged 13 to 18 undergoing heart transplantation. Recipients were divided into quintiles (Q1-Q5) based on donor-to-recipient predicted heart mass ratios (PHMR). Primary end-point was graft survival at 5 years.

RESULTS

Two thousand sixty-one adolescent heart transplant recipients between January 1994 and September 2019 were retrospectively analyzed. The median PHMR's for each quintile was 0.84 (0.59-0.92), 0.97 (0.92-1.02), 1.08 (1.02-1.14), 1.21 (1.14-1.30), and 1.44 (1.30-2.31). Kaplan-Meier survival curves demonstrated comparable survival across all quintiles of PHMR (p = 0.9). Multivariate Cox regression showed no significant difference in graft failure of the outer quintiles when compared to the middle quintile (Q1: 1.04 HR, p = 0.80; Q2: 1.02 HR, p = 0.89; Q4: 1.19 HR, p = 0.28; Q5: 1.02 HR, p = 0.89). Significant covariates included transplant year (HR: 0.95, p < 0.0001), serum bilirubin (HR: 1.04, p = 0.0004), ECMO at transplantation (HR: 2.85, p < 0.0001), and underlying diagnosis of dilated cardiomyopathy (vs congenital heart disease, HR: 0.66, p = 0.0004).

CONCLUSIONS

Matching by PHM is not associated with survival or risk in adolescent heart transplant recipients. Our results underscore the ongoing need to develop an improved size-matching method in pediatric heart transplantation.

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.

Evidence supporting total cardiac volumes instead of weight for transplant size-matching

Total cardiac volume (TCV)-based size matching for heart transplantation offers individualization in size matching that increases the number of suitable donors. Here we describe our clinical protocol for using TCV to determine an acceptable donor weight range for heart transplant candidates. We compare candidate imaging-derived TCV to a nomogram of subjects with normal TCV to determine a precise maximum donor weight at the time of listing. For nearly half of our transplant patients, we have increased weight range by an average of 70% with no oversizing related adverse events, such as delayed chest closure to avoid tamponade or bronchial compression. Widespread adoption of TCV-based size matching can lead to a more efficient heart allocation system by the data-driven bypass of poor size matches.

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.

A coordinated approach to improving pediatric heart transplant waitlist outcomes: A summary of the ACTION November 2019 waitlist outcomes committee meeting

The number of children needing heart transplantation continues to rise. Although improvements in heart failure therapy, particularly durable mechanical support, have reduced waitlist mortality, the number of children who die while waiting for a suitable donor organ remains unacceptably high. Roughly, 13% of children and 25% of infants on the heart transplant waitlist will not survive to transplantation. With this in mind, the Advanced Cardiac Therapies Improving Outcomes Collaborative Learning Network (ACTION), through its Waitlist Outcomes Committee, convened a 2-day symposium in Ann Arbor, Michigan, from 2-3 November 2019, to better understand the factors that contribute to pediatric heart transplant waitlist mortality and to focus future efforts on improving the organ allocation rates for children needing heart transplantation. Using improvement science methodology, the heart failure-transplant trajectory was broken down into six key steps, after which modes of failure and opportunities for improvement at each step were discussed. As a result, several projects aimed at reducing waitlist mortality were initiated.