Objective: Pediatric pulmonary vein stenosis (PVS) is associated with substantial morbidity and mortality for the subset of patients with recurrent or progressive disease. The molecular mechanisms underlying the development and trajectory of PVS remain unclear. This study characterizes the transcriptome of clinical and phenotypic subtypes of PVS. Methods: Bulk RNA sequencing analysis was performed on human pulmonary vein tissue samples obtained from surgical interventions for pediatric patients with PVS. Transcriptomic profiles were compared for primary versus postrepair PVS as well as aggressive versus nonaggressive clinical phenotypes. Principal component analysis was performed, the differential gene expression quantified, and pathway analysis conducted on the basis of Gene Ontology, Kyoto Encyclopedia of Genes and Genomes, and Reactome. Results: When we compared aggressive (Agg) primary pulmonary vein stenosis (PPVS) versus nonaggressive (NonAgg) PPVS, differences were noted in the genes associated in extracellular matrix regulation and PIEZO1, a mechanosensitive receptor present in endothelial cells. In addition, there were notable changes in cardiac muscle contractility, calcium handling, respiratory and energy metabolism. These results point to a potential mechanism for aggressive PPVS phenotype, attributable to an overexpression of PIEOZ1 in response to elevated shear stress, subsequent activation of intracellular signaling pathways, and leading to reduced contractility and intracellular calcium transients within cardiomyocytes. Conclusions: These results suggests that aggressive PPVS phenotype may be driven by an increase in PIEZO1 expression and subsequent changes in extracellular matrix production. The clinical and therapeutic relevance of PIEZO1 warrant further investigation.

Background Identification of individuals at risk for major adverse cardiovascular events is essential for contemporary management of patients with repaired tetralogy of Fallot. We sought to identify clinical and cardiovascular magnetic resonance imaging (CMR) predictors of adverse clinical outcomes in repaired tetralogy of Fallot. Methods Children and adults prospectively enrolled in the CORRELATE (Comprehensive Outcomes Registry Late After Tetralogy of Fallot Repair) registry followed in North American, European, and Asian centers were studied. All patients had at least moderate pulmonary regurgitation and CMR at enrollment. Time‐to‐event analyses were performed from CMR completion to primary outcome, defined as mortality, resuscitated sudden death, sustained ventricular arrhythmia, or heart failure admission. Principal component analysis was used to create distinct CMR scores that collectively captured 80% of the variance among 10 CMR measures (systolic function, biventricular volumes/mass, and biatrial areas). Results In 720 patients (55% male, median age 30.3±14 years, 78% adult) with mean follow‐up 5.7±1.8 years, the primary outcome occurred in 38 patients (5.2%) at a rate of 0.9/100 patient‐years. A well‐calibrated risk scoring system was created for prediction of the primary outcome at 5 years based on 5 predictors: age, diabetes, right ventricular systolic pressure, and 2 CMR principal component scores (predominantly reflecting atrial areas in the first principal component score and ventricular volumes in the second principal component score) (c‐statistic for the composite risk score 0.79 [95% Cl, 0.71–0.88]). Conclusions Clinical and imaging characteristics can contribute to risk prediction in repaired tetralogy of Fallot. Further study will be required to evaluate the utility of a risk scoring system for identification of individuals who may benefit from enhanced surveillance, intensified medical therapy, and/or optimally timed intervention.

Background: Pediatric pulmonary vein stenosis (PVS) is associated with substantial morbidity and mortality for the subset of patients with recurrent or progressive disease. The molecular mechanisms underlying the development and trajectory of PVS remain unclear. This study characterizes the transcriptome of clinical and phenotypic subtypes of PVS. Methods: Bulk RNA sequencing analysis was performed on human pulmonary vein tissue samples obtained from surgical interventions for pediatric patients with PVS. Transcriptomic profiles were compared for primary versus post-repair PVS as well as aggressive versus non-aggressive clinical phenotypes. Principal component analysis was performed, the differential gene expression quantified, and pathway analysis conducted based on gene ontology, KEGG and Reactome. Results: When comparing AggPPVS vs NonAggPPVS, differences were noted in the genes associated in extracellular matrix regulation and PIEZO1, a mechanosensitive receptor present in endothelial cells. In addition, there were notable changes in cardiac muscle contractility, calcium handling, respiratory and energy metabolism. These results point to a potential mechanism for aggressive PPVS phenotype, due to an overexpression of PIEOZ1 in response to elevated shear stress, subsequent activation of intracellular signaling pathways and leading to reduced contractility and intracellular calcium transients with cardiomyocytes. Conclusions: The result of this study suggests that aggressive PPVS phenotype is caused by an increase in PIEZO1 expression and subsequent changes in extracellular matrix production, heart muscle contractility and changes in calcium transients within cardiomyocytes. These results provide a potential target for therapeutic invention for primary PPVS by inhibiting the activity of PIEZO1. This could potentially reduce morbidity in this patient population. ### Competing Interest Statement The authors have declared no competing interest.

Background: Pediatric pulmonary vein stenosis (PVS) is often progressive and treatment-refractory, requiring multiple interventions. Hybrid pulmonary vein interventions (HPVIs), involving intraoperative balloon angioplasty or stent placement, leverage surgical access and customization to optimize patency while facilitating future transcatheter procedures. We review our experience with HPVI and explore potential applications of this collaborative approach. Methods: Retrospective chart review of all HPVI cases between 2009 to 2023. Results: Ten patients with primary (n = 5) or post-repair (n = 5) PVS underwent HPVI at median age of 12.7 months (range 6.6 months-9.5 years). Concurrent surgical PVS repair was performed in 7/10 cases. Hybrid pulmonary vein intervention was performed on 17 veins, 13 (76%) with prior surgical or transcatheter intervention(s). One patient underwent intraoperative balloon angioplasty of an existing stent. In total, 18 stents (9 bare metal [5-10 mm diameter], 9 drug eluting [3.5-5 mm diameter]) were placed in 16 veins. At first angiography (median 48 days [range 7 days-2.8 years] postoperatively), 8 of 16 (50%) HPVI-stented veins developed in-stent stenosis. Two patients died from progressive PVS early in the study, one prior to planned reintervention. Median time to first pulmonary vein reintervention was 86 days (10 days-2.8 years; 8/10 patients, 13/17 veins). At median survivor follow-up of 2.2 years (2.3 months-13.1 years), 1 of 11 surviving HPVI veins were completely occluded. Conclusions: Hybrid pulmonary vein intervention represents a viable adjunct to existing PVS therapies, with promising flexibility to address limitations of surgical and transcatheter modalities. Reintervention is anticipated, necessitating evaluation of long-term benefits and durability as utilization increases.

Feature Editor's Introduction—Leaders in surgery are expected to deliver the highest quality clinical, academic, and educational outcomes. At the same time, surgical leaders must deal with a very complex administrative environment to bring the momentum and often the intensity to propel a program forward. Herein, 2 world-renowned surgeons with extensive leadership experience discuss the complexity and challenges of building a high level of performance into congenital heart programs.Igor E. Konstantinov, MD, PhD, FRACS

We present a case of anatomic repair of dextro-transposition of the great arteries (d-TGA) with ventricular septal defect (VSD) in a 55-year-old man who presented with acute heart failure. This case highlights the importance of multimodal imaging and multidisciplinary involvement in developing a comprehensive surgical and medical plan for adults with congenital heart disease. We think this is the oldest reported patient undergoing anatomic surgical repair of d-TGA with VSD.

Our core mission as a community of congenital heart surgeons is to ensure the safety and quality of care delivered to our patients and their families. As content experts, we are best equipped to understand and evaluate issues that threaten our core mission and develop strategies to respond to these threats.

OBJECTIVES:Symptomatic neonates and infants with Ebstein anomaly (EA) require complex management. A group of experts was commissioned by the American Association for Thoracic Surgery to provide a framework on this topic focusing on risk stratification and management. METHODS:The EA Clinical Congenital Practice Standards Committee is a multinational and multidisciplinary group of surgeons and cardiologists with expertise in EA. A citation search in PubMed, Embase, Scopus, and Web of Science was performed using key words related to EA. The search was restricted to the English language and the year 2000 or later and yielded 455 results, of which 71 were related to neonates and infants. Expert consensus statements with class of recommendation and level of evidence were developed using a modified Delphi method, requiring 80% of members votes with at least 75% agreement on each statement. RESULTS:When evaluating fetuses with EA, those with severe cardiomegaly, retrograde or bidirectional shunt at the ductal level, pulmonary valve atresia, circular shunt, left ventricular dysfunction, or fetal hydrops should be considered high risk for intrauterine demise and postnatal morbidity and mortality. Neonates with EA and severe cardiomegaly, prematurity (<32 weeks), intrauterine growth restriction, pulmonary valve atresia, circular shunt, left ventricular dysfunction, or cardiogenic shock should be considered high risk for morbidity and mortality. Hemodynamically unstable neonates with a circular shunt should have emergent interruption of the circular shunt. Neonates in refractory cardiogenic shock may be palliated with the Starnes procedure. Children may be assessed for later biventricular repair after the Starnes procedure. Neonates without high-risk features of EA may be monitored for spontaneous closure of the patent ductus arteriosus (PDA). Hemodynamically stable neonates with significant pulmonary regurgitation at risk for circular shunt with normal right ventricular systolic pressure should have an attempt at medical closure of the PDA. A medical trial of PDA closure in neonates with functional pulmonary atresia and normal right ventricular systolic pressure (>20-25 mm Hg) should be performed. Neonates who are hemodynamically stable without pulmonary regurgitation but inadequate antegrade pulmonary blood flow may be considered for a PDA stent or systemic to pulmonary artery shunt. CONCLUSIONS:Risk stratification is essential in neonates and infants with EA. Palliative comfort care may be reasonable in neonates with associated risk factors that may include prematurity, genetic syndromes, other major medical comorbidities, ventricular dysfunction, or sepsis. Neonates who are unstable with a circular shunt should have emergent interruption of the circular shunt. Neonates who are unstable are most commonly palliated with the Starnes procedure. Neonates who are stable should undergo ductal closure. Neonates who are stable with inadequate pulmonary flow may have ductal stenting or a systemic-to-pulmonary artery shunt. Subsequent procedures after Starnes palliation include either single-ventricle palliation or biventricular repair strategies.

BACKGROUNDWe describe outcomes and management strategies for single ventricle and bilaterally discontinuous pulmonary arteries (PAs) originating from bilateral ductus arteriosus.METHODSWe reviewed 22 patients with aforementioned anatomy and PA centralization from 1995-2023, excluding those with biventricular repair.RESULTSMedian age at centralization was 9 days (range 0 days-2 years). Centralization was performed with systemic-to-pulmonary shunt (n=20, 91%; 2 following bilateral ductal stents) or bidirectional cavopulmonary connection (n=2, 9%) via pericardial roll (n=14, 64%), patch-augmented direct anastomosis (n=7, 32%), and interposition graft (n=1, 5%) techniques. Concurrent total anomalous pulmonary venous connection (TAPVC, n=11, 50%) was associated with significantly inferior survival (P=.01). Five patients (23%) died at a median of 59 (6-257) days post-centralization, all with non-cardiac TAPVC. At latest follow-up for 17 survivors (median 13.5 [0.5-25.1] years post-centralization), 12 completed Fontan, 4 completed second stage palliation, and 1 was transplanted prior to second stage palliation. Fourteen patients (64%) required PA reintervention, including 3 with reoperations independent of staged palliation. Baseline to pre-second stage echocardiography demonstrated branch PA growth with significantly increased diameters (left P=.0006, right P=.0002); z-scores significantly increased for right (P=.004) but not left (P=.11).CONCLUSIONSSuccessful single ventricle palliation is possible, though high-risk, for patients with bilateral discontinuous ductal PAs. Early post-centralization mortality remains substantial, particularly with associated non-cardiac TAPVC. Many require reintervention to maintain PA growth, typically concurrently with staged palliation.

BACKGROUND Early clinical outcomes data for adjunctive systemic sirolimus therapy (SST) for moderate to severe pediatric pulmonary vein stenosis (PVS) are promising but limited. OBJECTIVES The authors aimed to characterize a cohort of patients treated with SST to determine if SST was associated with a reduction in frequency of PVS interventions. METHODS Medical records of 45 patients with PVS treated with SST for >= 1 month from 2015 to 2022 were retrospectively reviewed. PVS intervention rates pre-SST and on-SST were compared using generalized Poisson mixed models, accounting for paired intervals within each patient. In addition to an unadjusted model, an adjusted model accounted for age at interval start, PVS type, sex, prematurity, and concurrent antiproliferative therapy. Mean number of PVS interventions per patient over time (mean cumulative function) were also compared for these intervals in an unpaired fashion. Kaplan-Meier estimates were used to quantify survival over time. RESULTS Median per-patient PVS intervention rate (interventions/year) was 5 pre-SST and 1.7 on-SST, significantly lower on-SST in the unadjusted and adjusted models (P < 0.001, both). Patients accrued an increased cumulative number of interventions over time pre-SST compared to on-SST by mean cumulative function (P < 0.001). Median duration of SST was 1.7 years and median follow-up time from SST initiation was 2.7 years. There were 6 mortalities at a median of 1.1 years (range, 4.4 months-6.5 years) following SST initiation. CONCLUSIONS SST was associated with a reduction in frequency of PVS interventions. Prospective studies are warranted to determine potential causality, delineate patient-and vein-level outcomes, and determine optimal therapeutic duration. (c) 2024 The Authors. Published by Elsevier on behalf of the American College of Cardiology Foundation. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

Introduction: Anomalous aortic origin of a coronary artery (AAOCA) confers risk of sudden death in the young. Paucity of data exists in AAOCA with high take-off (ht-AAOCA) from the aorta. Hypothesis: Patients with ht-AAOCA may be at risk of inducible myocardial ischemia and surgery might be indicated in a small subset with good medium-term outcomes. Methods: Patients with ht-AAOCA, defined as origin at the sinotubular junction and above by CTA, <25 years old were prospectively enrolled. Myocardial functional studies were obtained under provocative stress: exercise stress test, stress nuclear perfusion imaging, dobutamine stress cardiac MRI, or cardiac catherization (in select patients). These studies were repeated 3 months post-operatively (post-op) in surgical patients. Results: A total of 71 patients (45 male, 63%) with ht-AAOCA were enrolled, median age 15 [IQR 12; 19] years. ht-AAOCA of the right (ht-AAORCA) was seen in 66/71 patients (93%): 15 (23%) had exertional symptoms, 13 (20%) had nonexertional symptoms, 14 (21%) had both, 24 (37%) were asymptomatic. Ht-AAOCA of the left (ht-AAOLCA) was seen in 5/71 patients (7%), only 1 (20%) had exertional symptoms. In ht-AAORCA patients, 50/66 (76%) had abnormal ostia and 6/66 (9%) juxtacommissural origin, as compared to 3/5 (60%) and 2/5 (40%), respectively, in ht-AAOLCA patients. Average intramural course in ht-AAORCA was 4.46 mm and 2.36 mm in ht-AAOLCA. Abnormal functional testing corresponding to the affected territory was seen in 11/71 (15%) ht-AAOCA patients. Surgery was recommended for 18/71 (25%) patients due to concerning symptoms, coronary anatomy, or abnormal functional testing. Of these, 13/18 (72%) underwent coronary artery unroofing (in 12) or reimplantation (in 1), 3 declined surgery, 2 pending decision. All surgical patients have returned to unrestricted exercise after reassuring post-op studies, but 1/18 (6%) awaits completion. At median follow up of 1.8 years (range 0.1-8.9), all patients are alive and well, 93% are exercising with no restrictions. Conclusion: Although ht-AAOCA appears benign in most patients, 15% shows inducible myocardial ischemia. Surgery may be indicated in a subset of patients, with overall excellent medium-term outcomes and freedom from exercise restrictions.

BACKGROUND Comprehensive assessment of tetralogy of Fallot (TOF) outcomes extends beyond morbidity and mortality to incorporate patient-reported outcomes (PROs), including quality of life (QOL) and health status (HS).OBJECTIVES This study explored PROs in adolescents and adults with TOF and delineated variables associated with PROs. METHODS This was a cross-sectional observational study within a larger prospective registry of adolescents and adults with repaired TOF and moderate or greater pulmonary regurgitation from North America, Europe, and Asia. Participants completed PROs, including a QOL linear analogue scale (QOL-LAS) and an HS visual analogue scale (HS-VAS). Scores were classified according to age cohorts: <18, 18 to 25, 26 to 40, and >40 years.RESULTS The study included 607 patients (46.3% female; median age 28.5 years). Median QOL-LAS scores (0-100) were similar across age cohorts (85, 80, 80, 80; P = 0.056). Median HS-VAS scores (0-100) were lowest for the oldest cohort (77) compared with the 3 younger cohorts (85, 80, 80) (P = 0.004). With advancing age, there were increased reports of poor mobility (P < 0.001) and pain or discomfort (P = 0.004); problems in these dimensions were reported by 19.1% and 37.2% of patients aged >40 years, respectively. Of factors associated with superior PROs on multivariable regression modeling (ie, being White, being nonsyndromic, having employment, and having better left ventricular function; P < 0.05), asymptomatic status (functional class I) was the variable associated with the greatest number of QOL and HS measures (P < 0.001). CONCLUSIONS Strategies to improve TOF outcomes should consider PROs alongside conventional clinical variables. Factors associated with poorer PROs represent opportunities to intervene to improve the lives of patients with TOF. (J Am Coll Cardiol 2023;81:1937-1950) (c) 2023 by the American College of Cardiology Foundation.

Objective: To determine patient characteristics and outcomes after Norwood versus comprehensive stage II (COMPSII) for infants with critical left heart obstruction who had prior hybrid palliation (bilateral pulmonary artery banding +/- ductal stent).Methods: From 23 Congenital Heart Surgeons' Society institutions (2005-2020), 138 infants underwent hybrid palliation followed by either Norwood (n = 73, 53%) or COMPSII (n = 65). Baseline characteristics were compared between Norwood and COMPSII groups. Parametric hazard model with competing risk methodology was used to determine risk and factors associated with outcomes of Fontan, transplantation, or death.Results: Infants who underwent Norwood versus COMPSII had a higher prevalence of prematurity (26% vs 14%, P = .08), lower birth weight (median 2.8 vs 3.2 kg, P < .01) and less frequent ductal stenting (37% vs 99%; P < .01). Norwood was performed at a median age of 44 days and median weight of 3.5 kg, versus COMPSII at 162 days and 6.0 kg (both P<.01). Median follow-up was 6.5 years. At 5 years after Norwood and COMPSII, respectively; 50% versus 68% had Fontan (P = .16), 3% versus 5% had transplantation (P = .70), 40% versus 15% died (P = .10), and 7% versus 11% are alive without transition, respectively. For factors associated with either mortality or Fontan, only preoperative mechanical ventilation occurred more frequently in the Norwood group.Conclusions: Higher prevalence of prematurity, lower birth weight, and other patient-related characteristics in the Norwood versus COMPSII groups may influence differences in outcomes that were not statistically significant for this limited risk-adjusted cohort. The clinical decision regarding Norwood versus COMPSII after initial hybrid palliation remains challenging. (J Thorac Cardiovasc Surg 2023;166:943-54)

Backer and colleagues1 present a substantial body of work initiated by the Congenital Heart Surgeons' Society that outlines the recommendations of an expert panel regarding the classification, design, and development of centers performing pediatric heart surgery in the United States. The assembled panel of experts included membership from a wide array of representative centers and specialties and the group's thoughtful analysis has resulted in a comprehensive document that has been endorsed by the Board of Directors of the American Association for Thoracic Surgery (AATS).

Objective:Post-Norwood mortality remains high and unpredictable. Current models for mortality do not incorporate interstage events. We sought to determine the association of time-related interstage events, along with (pre)operative characteristics, with death post-Norwood and subsequently predict individual mortality.Methods:From the Congenital Heart Surgeons' Society Critical Left Heart Obstruction cohort, 360 neonates underwent Norwood operations from 2005 to 2016. Risk of death post-Norwood was modeled using a novel application of parametric hazard analysis, in which baseline and operative characteristics and time-related adverse events, procedures, and repeated weight and arterial oxygen saturation measurements were considered. Individual predicted mortality trajectories that dynamically update (increase or decrease) over time were derived and plotted.Results:After the Norwood, 282 patients (78%) progressed to stage 2 palliation, 60 patients (17%) died, 5 patients (1%) underwent heart transplantation, and 13 patients (4%) were alive without transitioning to another end point. In total, 3052 postoperative events occurred and 963 measures of weight and oxygen saturation were obtained. Risk factors for death included resuscitated cardiac arrest, moderate or greater atrioventricular valve regurgitation, intracranial hemorrhage/stroke, sepsis, lower longitudinal oxygen saturation, readmission, smaller baseline aortic diameter, smaller baseline mitral valve z-score, and lower longitudinal weight. Each patient's predicted mortality trajectory varied as risk factors occurred over time. Groups with qualitatively similar mortality trajectories were noted.Conclusions:Risk of death post-Norwood is dynamic and most frequently associated with time-related postoperative events and measures, rather than baseline characteristics. Dynamic predicted mortality trajectories for individuals and their visualization represent a paradigm shift from population-derived insights to precision medicine at the patient level.

Total anomalous pulmonary venous connection (TAPVC) constitutes a heterogeneous group of lesions in which all of the pulmonary veins are connected to the right atrium or its systemic venous tributaries. TAPVC is a rare malformation that accounts for approximately 1.5% of all cases of congenital heart disease. TAPVC classification is based on the level of connection of the anomalous connecting vein and the degree of obstruction. The clinical presentation of TAPVC depends on two critical elements: the degree of obstruction to the pulmonary venous drainage and the degree of obstruction to the atrial-level right-to-left shunt. Unobstructed TAPVC is sometimes difficult to diagnose in the first few days of life because patients may have very mild cyanosis and the absence of a murmur. Surgical repair of supracardiac TAPVC is accomplished via sternotomy with two venous cannulae and an aortic cannula.

PURPOSE:We reviewed all 64 articles ever published by The Congenital Heart Surgeons' Society (CHSS) Data Center to estimate the academic impact of these peer-reviewed articles. MATERIALS AND METHODS:The Congenital Heart Surgeons' Society has performed research based on 12 Diagnostic Inception Cohorts. The first cohort (Transposition) began enrolling patients on January 1, 1985. We queried PubMed to determine the number of publications that referenced each of the 64 journal articles generated by the datasets of the 12 Diagnostic Inception Cohorts that comprise the CHSS Database. Descriptive summaries of the data were tabulated using mean with standard deviation and median with range. RESULTS:Sixty-four peer-reviewed papers have been published based on the CHSS Database. Fifty-nine peer-reviewed articles have been published based on the 12 Diagnostic Inception Cohorts, and five additional articles have been published based on Data Science. Excluding the recently established Diagnostic Inception Cohort for patients with Ebstein malformation of tricuspid valve, the number of papers published per cohort ranged from 1 for coarctation to 11 for transposition of the great arteries. The 11 articles generated from the CHSS Transposition Cohort were referenced by a total of 111 articles (median number of references per journal article = 9 [range = 0-22, mean = 10.1]). Overall, individual articles were cited by an average of 11 (mean), and a maximum of 41 PubMed-listed publications. Overall, these 64 peer-reviewed articles based on the CHSS Database were cited 692 times in PubMed-listed publications. The first CHSS peer-reviewed article was published in 1987, and during the 35 years from 1987 to 2022, inclusive, the annual number of CHSS publications has ranged from 0 to 7, with a mean of 1.8 publications per year (median = 1, mode = 1). CONCLUSION:Congenital Heart Surgeons' Society studies are widely referenced in the pediatric cardiac surgical literature, with over 10 citations per published article. These cohorts provide unique information unavailable in other sources of data. A tool to access this analysis is available at: [https://data-center.chss.org/multimedia/files/2022/CAI.pdf].

BACKGROUND Hybrid palliation (bilateral pulmonary artery banding with or without ductal stenting) is an initial management strategy for infants with critical left heart obstruction and serves as palliation until subsequent operations are pursued. OBJECTIVES This study sought to determine patient characteristics and factors associated with subsequent outcomes for infants who underwent hybrid palliation. METHODS From 2005 to 2019, 214 of 1,236 prospectively enrolled infants within the Congenital Heart Surgeons' Society's critical left heart obstruction cohort underwent hybrid palliation across 24 institutions. Multivariable hazard modeling with competing risk methodology was performed to determine risk and factors associated with outcomes of biventricular repair, Fontan procedure, transplantation, or death. RESULTS Preoperative comorbidities (eg, prematurity, low birth weight, genetic syndrome) were identified in 70% of infants (150 of 214). Median follow-up was 7 years, ranging up to 17 years. Overall 12-year survival was 55%. At 5 years after hybrid palliation, 9% had biventricular repair, 36% had Fontan procedure, 12% had transplantation, 35% died without surgical endpoints, and 8% were alive without an endpoint. Factors associated with transplantation were absence of ductal stent, older age, absent interatrial communication, smaller aortic root size, larger tricuspid valve area z-score, and larger left ventricular volume. Factors associated with death were low birth weight, concomitant genetic syndrome, cardiopulmonary bypass use during hybrid palliation, moderate to severe tricuspid valve regurgitation, and smaller ascending aortic size. CONCLUSIONS Mortality remains high after hybrid palliation for infants with critical left heart obstruction. None-theless, hybrid palliation may facilitate biventricular repair for some infants and for others may serve as stabilization for intended functional univentricular palliation or primary transplantation. (J Am Coll Cardiol 2023;82:1427-1441) (c) 2023 by the American College of Cardiology Foundation.