Methylprednisolone for Heart Surgery in Infants - A Randomized, Controlled Trial.

BACKGROUND: Although perioperative prophylactic glucocorticoids have been used for decades, whether they improve outcomes in infants after heart surgery with cardiopulmonary bypass is unknown. METHODS: We conducted a multicenter, prospective, randomized, placebo-controlled, registry-based trial involving infants (<1 year of age) undergoing heart surgery with cardiopulmonary bypass at 24 sites participating in the Society of Thoracic Surgeons Congenital Heart Surgery Database. Registry data were used in the evaluation of outcomes. The infants were randomly assigned to receive prophylactic methylprednisolone (30 mg per kilogram of body weight) or placebo, which was administered into the cardiopulmonary-bypass pump-priming fluid. The primary end point was a ranked composite of death, heart transplantation, or any of 13 major complications. Patients without any of these events were assigned a ranked outcome based on postoperative length of stay. In the primary analysis, the ranked outcomes were compared between the trial groups with the use of odds ratios adjusted for prespecified risk factors. Secondary analyses included an unadjusted odds ratio, a win ratio, and safety outcomes. RESULTS: A total of 1263 infants underwent randomization, of whom 1200 received either methylprednisolone (599 infants) or placebo (601 infants). The likelihood of a worse outcome did not differ significantly between the methylprednisolone group and the placebo group (adjusted odds ratio, 0.86; 95% confidence interval [CI], 0.71 to 1.05; P = 0.14). Secondary analyses (unadjusted for risk factors) showed an odds ratio for a worse outcome of 0.82 (95% CI, 0.67 to 1.00) and a win ratio of 1.15 (95% CI, 1.00 to 1.32) in the methylprednisolone group as compared with the placebo group, findings suggestive of a benefit with methylprednisolone; however, patients in the methylprednisolone group were more likely than those in the placebo group to receive postoperative insulin for hyperglycemia (19.0% vs. 6.7%, P<0.001). CONCLUSIONS: Among infants undergoing surgery with cardiopulmonary bypass, prophylactic use of methylprednisolone did not significantly reduce the likelihood of a worse outcome in an adjusted analysis and was associated with postoperative development of hyperglycemia warranting insulin in a higher percentage of infants than placebo. (Funded by the National Center for Advancing Translational Sciences and others; STRESS ClinicalTrials.gov number, NCT03229538.).

Semilunar valve growth and function 10 years after infant heart transplantation: Predicting long-term outcomes of partial heart transplants.

INTRODUCTION: Partial heart transplants are a new type of pediatric transplant that replace defective heart valves with the parts of matched donor hearts containing the necessary valves. Short-term outcomes of partial heart transplants are excellent, but long-term outcomes are unknown. In order to predict the long-term outcomes of partial heart transplants, we evaluated long-term growth and function of semilunar heart valves transplanted in infancy as part of a heart transplant. METHODS: All children who underwent infant heart transplantation at a single center from 1997 to 2014 were included in this study. Children in whom echocardiograms after heart transplantation and after 10 years were not available for review were excluded. The echocardiograms were reviewed by two authors to analyze semilunar valve annulus diameters, Z-scores, peak valve gradients, and valve regurgitation. Statistical difference was determined using two-tailed, paired sample t-tests with Bonferroni correction for multiple comparisons. RESULTS: Data from 15 patients were analyzed. The aortic valve annulus averaged 1.3 cm (range 0.7-1.8 cm) immediately after transplantation and grew to an average of 1.7 cm (range 1.4-2.3 cm) after 10 years (p < .001). After 10 years, the aortic valve peak gradient avereraged 5.1 mmHg (range 2.1-15.5 mmHg) and none of the valves had more than trivial regurgitation. The pulmonary valve annulus averaged 1.5 cm (range 1.1-2.5 cm) immediately after transplantation and grew to an average of 2.1 cm (range 1.0-2.9 cm) after 10 years (p < .001). After 10 years, the pulmonary valve peak gradient averaged 4.3 mmHg (range 1.1-13.8 mmHg), and 7% of valves had moderate regurgitation. DISCUSSION: Semilunar heart valves transplanted in infancy as part of a heart transplant demonstrate statistically significant growth and excellent function after 10 years. This predicts excellent long-term outcomes of partial heart transplants.

The impact of heart valve and partial heart transplant models on the development of banking methods for tissues and organs: A concise review.

Cryopreserved human heart valves fill a crucial role in the treatment for congenital cardiac anomalies, since the use of alternative mechanical and xenogeneic tissue valves have historically been limited in babies. Heart valve models have been used since 1998 to better understand the impact of cryopreservation variables on the heart valve tissue components with the ultimate goals of improving cryopreserved tissue outcomes and potentially extrapolating results with tissues to organs. Cryopreservation traditionally relies on conventional freezing, employing cryoprotective agents, and slow cooling to sub-zero centigrade temperatures; but it is plagued by the formation of ice crystals and cell damage upon thawing. Researchers have identified ice-free vitrification procedures and developed a new rapid warming method termed nanowarming. Nanowarming is an emerging method that utilizes targeted application of energy at the nanoscale level to rapidly rewarm vitrified tissues, such as heart valves, uniformly for transplantation. Vitrification and nanowarming methods hold great promise for surgery, enabling the storage and transplantation of tissues for various applications, including tissue repair and replacement. These innovations have the potential to revolutionize complex tissue and organ transplantation, including partial heart transplantation. Banking these grafts addresses organ scarcity by extending preservation duration while preserving biological activity with maintenance of structural fidelity. While ice-free vitrification and nanowarming show remarkable potential, they are still in early development. Further interdisciplinary research must be dedicated to exploring the remaining challenges that include scalability, optimizing cryoprotectant solutions, and ensuring long-term viability upon rewarming in vitro and in vivo.

Partial Heart Transplantation - How to Change the System.

Partial heart transplantation is the first clinically successful approach to deliver growing heart valve implants. To date, 13 clinical partial heart transplants have been performed. However, turning partial heart transplantation into a routine procedure that is available to all children who would benefit from growing heart valve implants poses formidable logistical challenges. Firstly, a supply for partial heart transplant donor grafts needs to be developed. This challenge is complicated by the scarcity of donor organs. Importantly, the donor pools for orthotopic heart transplants, partial heart transplants and cadaver homografts overlap. Secondly, partial heart transplants need to be allocated. Factors relevant for equitable allocation include the indication, anatomical fit, recipient clinical status and time on the wait list. Finally, partial heart transplantation will require regulation and oversight, which only recently has been undertaken by the Food and Drug Administration, which regulates human cellular and tissue-based products. Overcoming these challenges will require a change in the system. Once this is achieved, partial heart transplantation could open new horizons for children who require growing tissue implants.

Days alive and out of hospital for children born with single-ventricle heart disease.

BACKGROUND: This study describes the illness burden in the first year of life for children with single-ventricle heart disease, using the metric of days alive and out of hospital to characterize morbidity and mortality. METHODS: This is a retrospective single-centre study of single-ventricle patients born between 2005 and 2021 who had their initial operation performed at our institution. Patient demographics, anatomical details, and hospitalizations were extracted from our institutional single-ventricle database. Days alive and out of hospital were calculated by subtracting the number of days hospitalized from number of days alive during the first year of life. A multivariable linear regression with stepwise variable selection was used to determine independent risk factors associated with fewer days alive and out of hospital. RESULTS: In total, 437 patients were included. Overall median number of days alive and out of hospital in the first year of life for single-ventricle patients was 278 days (interquartile range 157-319 days). In a multivariable analysis, low birth weight (<2.5kg) (b = -37.55, p = 0.01), presence of a dominant right ventricle (b = -31.05, p = 0.01), moderate-severe dominant atrioventricular valve regurgitation at birth (b = -37.65, p < 0.05), index hybrid Norwood operation (b = -138.73, p < 0.01), or index heart transplant (b = -158.41, p < 0.01) were all independently associated with fewer days alive and out of hospital. CONCLUSIONS: Children with single-ventricle heart defects have significant illness burden in the first year of life. Identifying risk factors associated with fewer days alive and out of hospital may aid in counselling families regarding expectations and patient prognosis.

Partial Heart Transplant in a Neonate With Irreparable Truncal Valve Dysfunction.

Importance: The treatment of neonates with irreparable heart valve dysfunction remains an unsolved problem because there are no heart valve implants that grow. Therefore, neonates with heart valve implants are committed to recurrent implant exchanges until an adult-sized valve can fit. Objective: To deliver the first heart valve implant that grows. Design, Setting, and Participants: Case report from a pediatric referral center, with follow-up for more than 1 year. Participants were a recipient neonate with persistent truncus arteriosus and irreparable truncal valve dysfunction and a donor neonate with hypoxic-ischemic brain injury. Intervention: First-in-human transplant of the part of the heart containing the aortic and pulmonary valves. Main Outcomes and Measures: Transplanted valve growth and hemodynamic function. Results: Echocardiography demonstrated adaptive growth and excellent hemodynamic function of the partial heart transplant valves. Conclusions and Relevance: In this child, partial heart transplant delivered growing heart valve implants with a good outcome at age 1 year. Partial heart transplants may improve the treatment of neonates with irreparable heart valve dysfunction.

Hybrid approach to pulmonary vein stenting after Fontan palliation.

Pulmonary vein stenosis is poorly tolerated in patients who have undergone Fontan palliation and typically requires surgical or transcatheter intervention. Percutaneous transcatheter approaches to intervention can be technically difficult due to challenging anatomy. A hybrid per-atrial transcatheter approach for stenting pulmonary veins provides a direct approach to the pulmonary veins and has the potential to improve safety and efficacy of this complex intervention. We describe our experience with hybrid per-atrial pulmonary vein stenting in three patients with pulmonary vein stenosis following Fontan palliation.

Repeat pediatric heart transplantation: A united network for organ sharing database analysis.

BACKGROUND: A history of congenital heart disease and previous transplantation are each independently associated with worse survival following pediatric heart transplantation. This study aimed to evaluate the characteristics and outcomes of children undergoing repeat heart transplantation in the United States based on the underlying diagnosis. METHODS: The United Network for Organ Sharing database was used to identify 8111 patients aged <18 years undergoing isolated heart transplantation from 2000 to 2021, including 435 (5.4%) repeat transplants. Restricted cubic spline analysis assessed the non-linear relationship between inter-transplant interval and the primary outcome of all-cause mortality or re-transplantation. Multivariable Cox regression assessed the impact of re-transplantation on the primary outcome. Median follow-up was 5.0 (interquartile range 1.9-9.9) years. RESULTS: Repeat transplant patients were older (median age 12 vs. 4 years; p < .001), and less likely to be in UNOS status 1A (66.0%, n = 287 vs. 81.0% n = 6217; p < .001) than primary transplant patients. Freedom from the primary outcome was 51.4% (95% confidence interval [CI] 45.5-57.2) among repeat transplants and 70.5% (95% CI 69.2-71.8) among primary transplants at 10 years (p < .001). Among repeat transplant patients, the relative hazard of the primary outcome became non-significant when the inter-transplant interval >3.6 years. Congenital heart disease was an independent predictor of mortality among primary (HR 1.8, 95% CI 1.6-1.9) but not repeat transplant (HR 1.1, 95% CI .8-1.6) patients. CONCLUSIONS: Long-term outcomes remain poor for patients undergoing repeat heart transplantation, particularly those with an inter-transplant interval <3.6 years. Underlying diagnosis does not impact outcomes after repeat transplantation, after accounting for other risk factors.

Single stage biventricular repair of hypoplastic right ventricle with straddling tricuspid valve.

We present the case of a five-year-old child with an inlet ventricular septal defect, subpulmonic stenosis, hypoplastic right ventricle, and straddling tricuspid valve who received a successful one-stage biventricular repair with right ventricular rehabilitation, right ventricular outflow tract augmentation, papillary muscle transposition, ventricular septal defect closure, and fenestrated atrial septation. This report outlines the surgical decision making and operative technique.

Outcomes of truncal valve replacement in neonates and infants: a meta-analysis.

BACKGROUND: Infants with truncus arteriosus typically undergo repair by repurposing the truncal valve as the neo-aortic valve and using a valved conduit homograft for the neo-pulmonary valve. In cases where the native truncal valve is too insufficient for repair, it is replaced, but this is a rare occurrence with a paucity of data, especially in the infant population. Here, we conduct a meta-analysis to better understand the outcomes of infant truncal valve replacement during the primary repair of truncus arteriosus. METHODS: We systematically reviewed PubMed, Scopus, and CINAHL for all studies reporting infant (<12 months) truncus arteriosus outcomes between 1974 and 2021. Exclusion criteria were studies which did not report truncal valve replacement outcomes separately. Data extracted included valve replacement type, mortality, and reintervention. Our primary outcome was early mortality, and our secondary outcomes were late mortality and reintervention rates. RESULTS: Sixteen studies with 41 infants who underwent truncal valve replacement were included. The truncal valve replacement types were homografts (68.8%), mechanical valves (28.1%), and bioprosthetic valves (3.1%). Overall early mortality was 49.4% (95% CI: 28.4-70.5). The pooled late mortality rate was 15.3%/year (95% CI: 5.8-40.7). The overall rate of truncal valve reintervention was 21.7%/year (95% CI: 8.4-55.7). CONCLUSIONS: Infant truncal valve replacement has poor early and late mortality as well as high rates of reintervention. Truncal valve replacement therefore remains an unsolved problem in congenital cardiac surgery. Innovations in congenital cardiac surgery, such as partial heart transplantation, are required to address this.

Predictors of increased postoperative length of stay after complete atrioventricular canal repair.

BACKGROUND: The optimal timing of surgical repair for infants with complete atrioventricular canal defect remains controversial, as there are risks to both early and late repair. We address this debate by investigating the association of various risk factors, including age and weight at surgery, markers of failure to thrive, and pulmonary vascular disease, with postoperative length of stay following complete atrioventricular canal repair. METHODS: Infants who underwent repair of complete atrioventricular canal were identified from our institutional Society of Thoracic Surgeons Congenital Heart Surgery Database. Additional clinical data were collected from the electronic medical record. Descriptive statistics were computed. Associations between postoperative length of stay and covariates of interest were evaluated using linear regression with bootstrap aggregation. RESULTS: From 2001 to 2020, 150 infants underwent isolated complete atrioventricular canal repair at our institution. Pre-operative failure to thrive and evidence of pulmonary disease were common. Surgical mortality was 2%. In univariable analysis, neither weight nor age at surgery were associated with mortality, postoperative length of stay, duration of mechanical ventilation, or post-operative severe valvular regurgitation. In multivariable analysis of demographic and preoperative clinical factors using bootstrap aggregation, increased postoperative length of stay was only significantly associated with previous pulmonary artery banding (33.9 day increase, p = 0.03) and preoperative use of supplemental oxygen (19.9 day increase, p = 0.03). CONCLUSIONS: Our analysis shows that previous pulmonary artery banding and preoperative use of supplemental oxygen were associated with increased postoperative length of stay after complete atrioventricular canal repair, whereas age and weight were not. These findings suggest operation prior to the onset of pulmonary involvement may be more important than reaching age or weight thresholds.

Introducing thymus for promoting transplantation tolerance.

Establishing tolerance remains a central, if elusive, goal of transplantation. In solid-organ transplantation, one strategy for inducing tolerance has been cotransplantation of various forms of thymic tissue along with another organ. As one of the biological foundations of central tolerance, thymic tissue carries with it the ability to induce tolerance to any other organ or tissue from the same donor (or another donor tissue-matched to the thymic tissue) if successfully transplanted. In this review, we outline the history of this approach as well as work to date on its application in organ transplantation, concluding with future directions. We also review our experience with allogeneic processed thymus tissue for the treatment of congenital athymia, encompassing complete DiGeorge syndrome and other rare genetic disorders, and consider whether allogeneic processed thymic tissue implantation may offer a novel method for future experimentation with tolerance induction in organ transplantation.

Partial heart transplantation can ameliorate donor organ utilization.

BACKGROUND: The treatment of babies with unrepairable heart valve dysfunction remains an unsolved problem because there are no growing heart valve implants. However, orthotopic heart transplants are known to grow with recipients. AIM: Partial heart transplantation is a new approach to delivering growing heart valve implants, which involves transplantation of the part of the heart containing the valves only. In this review, we discuss the benefits of this procedure in children with unrepairable valve dysfunction. CONCLUSION: Partial heart transplantation can be performed using donor hearts with poor ventricular function and slow progression to donation after cardiac death. This should ameliorate donor heart utilization and avoid both primary orthotopic heart transplantation in children with unrepairable heart valve dysfunction and progression of these children to end-stage heart failure.

Sustained Total All-Region (STAR) perfusion for Norwood reconstruction with complex intracardiac repair.

We present the case of a newborn with complex congenital heart disease who was treated with a neonatal Norwood operation and total anomalous pulmonary venous return repair. During the Norwood reconstruction, a novel technique was utilized to perfuse the head, lower body, and heart continuously to minimize ischemic injury.

Overcoming underpowering: Trial simulations and a global rank end point to optimize clinical trials in children with heart disease.

BACKGROUND: Randomized controlled trials (RCTs) in children with heart disease are challenging and therefore infrequently performed. We sought to improve feasibility of perioperative RCTs for this patient cohort using data from a large, multicenter clinical registry. We evaluated potential enrollment and end point frequencies for various inclusion cohorts and developed a novel global rank trial end point. We then performed trial simulations to evaluate power gains with the global rank end point and with use of planned covariate adjustment as an analytic strategy. METHODS: Data from the Society of Thoracic Surgery-Congenital Heart Surgery Database (STS-CHSD, 2011-2016) were used to support development of a consensus-based global rank end point and for trial simulations. For Monte Carlo trial simulations (n = 50,000/outcome), we varied the odds of outcomes for treatment versus placebo and evaluated power based on the proportion of trial data sets with a significant outcome (P < .05). RESULTS: The STS-CHSD study cohort included 35,967 infant index cardiopulmonary bypass operations from 103 STS-CHSD centers, including 11,411 (32%) neonatal cases and 12,243 (34%) high-complexity (Society of Thoracic Surgeons-European Association for Cardio-Thoracic Surgery mortality category ≥4) cases. In trial simulations, study power was 21% for a mortality-only end point, 47% for a morbidity and mortality composite, and 78% for the global rank end point. With covariate adjustment, power increased to 94%. Planned covariate adjustment was preferable to restricting to higher-risk cohorts despite higher event rates in these cohorts. CONCLUSIONS: Trial simulations can inform trial design. Our findings, including the newly developed global rank end point, may be informative for future perioperative trials in children with heart disease.

Rationale and design of the STeroids to REduce Systemic inflammation after infant heart Surgery (STRESS) trial.

For decades, physicians have administered corticosteroids in the perioperative period to infants undergoing heart surgery with cardiopulmonary bypass (CPB) to reduce the postoperative systemic inflammatory response to CPB. Some question this practice because steroid efficacy has not been conclusively demonstrated and because some studies indicate that steroids could have harmful effects. STRESS is a randomized, placebo-controlled, double-blind, multicenter trial designed to evaluate safety and efficacy of perioperative steroids in infants (age < 1 year) undergoing heart surgery with CPB. Participants (planned enrollment = 1,200) are randomized 1:1 to methylprednisolone (30 mg/kg) administered into the CPB pump prime versus placebo. The trial is nested within the existing infrastructure of the Society of Thoracic Surgeons Congenital Heart Surgery Database. The primary outcome is a global rank score of mortality, major morbidities, and hospital length of stay with components ranked commensurate with their clinical severity. Secondary outcomes include several measures of major postoperative morbidity, postoperative hospital length of stay, and steroid-related safety outcomes including prevalence of hyperglycemia and postoperative infectious complications. STRESS will be one of the largest trials ever conducted in children with heart disease and will answer a decades-old question related to safety and efficacy of perioperative steroids in infants undergoing heart surgery with CPB. The pragmatic "trial within a registry" design may provide a mechanism for conducting low-cost, high-efficiency trials in a heretofore-understudied patient population.

Proteomic Analysis of Infants Undergoing Cardiopulmonary Bypass Using Contemporary Ontological Tools.

BACKGROUND: Cardiopulmonary bypass (CPB) is essential for the repair of many congenital cardiac defects in infants but is associated with significant derangements in hemostasis and systemic inflammation. As a result, hemorrhagic complications and thrombosis are major challenges in the management of children requiring CPB or extracorporeal membrane oxygenation. Conventional clinical laboratory tests capture individual hemostatic derangements (low platelets, elevated fibrinogen) but fail to describe the complex, overlapping interactions among the various components of coagulation, including cellular interactions, contact activation, fibrinolysis, and inflammation. Given recent advances in analytic tools for identifying protein-protein interactions in the plasma proteome, we hypothesized that an unbiased proteomic analysis would help identify networks of interacting proteins for further investigation in pediatric CPB. MATERIALS AND METHODS: Infants up to 1 y of age were enrolled. Plasma samples were collected at 0, 1, 4, and 24 h after CPB. Mass spectrometry was used to identify proteins undergoing changes in concentration after CPB, and STRING and ToppGene tools were used to identify biological networks. Two-dimensional difference gel electrophoresis identified changes in protein concentrations. Inflammatory markers were assessed by enzyme-linked immunosorbent assay at the same time points. RESULTS: Ten infants with cardiac anomalies requiring surgery and CPB were enrolled; no major complications were recorded (median age, 127.5 d; interquartile range, 181.25 d). Using two-dimensional difference gel electrophoresis, >1400 individual protein spots were observed, and 89 proteins demonstrated change in concentration >30% with P < 0.02 when comparing 1, 4, or 24 h to baseline. Among protein spots with significant changes in concentration after CPB, 29 were identified with mass spectrometry (33%). In our interrogation of functional associations among these differentially expressed proteins, our results were dominated by the acute phase response, coagulation, and cell signaling functional categories. Among cytokines analyzed by enzyme-linked immunosorbent assay, IL-2, IL-8, and IL-10 were elevated at 4 h but normalized by 24 h, whereas IL-6 was persistently elevated. CONCLUSIONS: Infants manifest a robust response to CPB that includes overlapping, complex pathways. Further investigation of interactions among immune, coagulation, and cell signaling systems may lead to novel therapeutics or biomarkers useful in the management of infants requiring CPB.

Initial Application of a Bicuspid Aortic Annuloplasty Ring in Pediatric Cardiac Surgery.

Aortic stenosis and aortic insufficiency (AI) are common valvular conditions that may necessitate repair or replacement of the aortic valve. Aortic valve replacement is associated with higher long-term complications and thus, a consistent, reliable method of repair is needed. This is especially true in the pediatric population where lifelong anticoagulation and development of recurrent aortic stenosisor aortic insufficiency are especially problematic. The Hemispherical Aortic Annuloplasty Reconstruction Technology ring has been developed and used for annular stabilization in adults with success, though its efficacy in the pediatric population has yet to be demonstrated. Herein, we discuss the use of a geometric ring in aortic valve repair for the pediatric patient.

Biventricular Conversion in the Borderline Hypoplastic Heart.

PURPOSE OF REVIEW: The development of biventricular repair and conversion pathways for patients with borderline hypoplastic heart disease represents an area of recent inquiry and innovation. This review summarizes emerging techniques and novel treatment algorithms for borderline hypoplastic heart disease with a focus on surgical advances within the last 10 years. RECENT FINDINGS: Many patients with borderline hypoplastic heart disease are amenable to primary biventricular repair, or biventricular conversion following single-ventricle palliation coupled with ventricular rehabilitation strategies. New insights into the potential for growth and recovery of borderline ventricles have been uncovered. However, questions remain regarding optimal patient selection and the long-term outcomes of select patient groups treated with single-ventricle palliation versus biventricular repair/conversion or transplantation. Efforts to direct a greater proportion of borderline hypoplastic heart patients towards a biventricular circulation are accelerating and represent important avenues for progress and future research in the field of congenital heart disease.

Implantation of a HeartMate 3 ventricular assist device in a 21-kg pediatric patient with Fontan failure.

AIMS: The HeartMate 3 (HM3) ventricular assist device (VAD) is gaining popularity in adults due to a favorable risk profile. However, reports of HM3 use in children are limited, potentially due to concerns with device size. MATERIALS AND METHODS: Here we report the successful use of an HM3-VAD as a bridge to transplantation in a 21 kg (BSA 0.84), an 8-year-old male child with Fontan failure on home inotropes. RESULTS: Urgent VAD implantation was performed. The standard adult sewing ring was used. The tricuspid valve and papillary muscles were completely excised from the ventricular cavity to prevent inflow obstruction. The pump was placed in the left pleural space. Outflow graft and driveline implantation were routine. VAD function appeared excellent with a reduction in Fontan pressures and improved kidney and liver function. Reoperation was required once to rule out tamponade and twice to evacuate a recurrent right hemothorax. The patient was discharged 3 months later in good condition and underwent successful heart transplantation 10 months after VAD placement. DISCUSSION: This report demonstrates the feasibility of HM3-VAD implantation in a 21-kg Fontan patient, suggesting HM3 size is not a prohibitive limitation at this weight.