Hypoplastic Left Heart Syndrome With Atrial Level Restriction in the Era of Prenatal Diagnosis

Hybrid Interventions in Congenital Heart Disease

Hybrid interventions in congenital heart disease (CHD) embody the inherent collaboration between congenital interventional cardiology and cardiothoracic surgery. Hybrid approaches to complex and common lesions provide the opportunity to circumvent the limitations of patient size, vascular access, severity of illness, and anatomy that would otherwise be prohibitive to surgical and percutaneous techniques alone. This review describes several important hybrid approaches to interventions in CHD.

Current Understanding of Indications, Technical Aspects and Outcomes of Fetal Cardiac Interventions

With the improvement in the detection of congenital heart disease in fetal life, fetal cardiac interventions are pushing the envelope in hopes of either altering the natural history of disease or improving survival in certain high-risk lesions. These interventions include fetal aortic valvuloplasty for evolving hypoplastic left heart syndrome, fetal atrial septoplasty with or without atrial septal stenting for hypoplastic left heart syndrome and variants with intact or severely restrictive atrial septum, and fetal pulmonary valvuloplasty for severe pulmonary stenosis or pulmonary atresia with intact ventricular septum. This review discusses their indications, technical aspects, and outcomes based on available literature.

Labyrinthine cor triatriatum sinister in fetal hypoplastic left heart syndrome is associated with poor outcomes

OBJECTIVES

A subset of hypoplastic-left-heart-syndrome (HLHS) fetuses have a complex cor-triatriatum sinister that we named "labyrinthine-cor (L-cor)". We sought to determine the prevalence of L-cor in HLHS fetuses and hypothesized that it is associated with increased mortality.

METHODS

This single-center retrospective cohort study included all HLHS fetuses from January 2010-December 2020. Fetuses with other hypoplastic-left-heart variants, inadequate images, lack of follow-up and fetal atrial-septal interventions were excluded. RAS was defined as the ratio of pulmonary-vein forward-to-reverse velocity-time-integral (VTI) ≤ 5 and severe-RAS defined as VTI-ratio <3. Kaplan-Meier survival-analysis was performed for the primary outcome of transplant-free survival for 62 weeks after gestational-age of 30 weeks (∼1 year).

RESULTS

Of the 156 consecutive fetuses with HLHS, 11 (7.7%) had L-cor and 8/11 (72.7%) of these had RAS. When compared to HLHS-RAS without L-cor, fetuses with HLHS-RAS and L-cor were less likely to survive to 28 days (87% vs. 62.5%, p = 0.017) and to 1 year (69.6% vs. 25%, p = 0.029). When comparing by survival analysis, fetuses with severe-RAS with L-cor had lower survival compared severe-RAS without L-cor (p = 0.020).

CONCLUSION

L-cor in fetal HLHS is associated with increased mortality. Recognition of this finding is important for prognostication and atrial-septal-intervention planning.

Fetal cardiac intervention in hypoplastic left heart syndrome with intact or restrictive atrial septum, systematic review, and meta-analysis

To investigate outcomes of fetuses with hypoplastic left heart syndrome (HLHS) with an intact or restrictive atrial septum (I/RAS) managed expectantly or with fetal atrial septal intervention (FASI PubMed, Scopus, and Web of Science were searched systematically from inception until April 2023. Outcomes were classified by those who had FASI and those who had expectant management (EM). To estimate the overall proportion of each endpoint, a meta-analysis of proportions was employed using a random-effects model. Heterogeneity was assessed using the I2 value. Thirty-two studies reporting on 746 fetuses with HLHS and I/RAS met our inclusion criteria. Eleven studies (123 fetuses) were in the FASI group and 21 studies (623 fetuses) were in the EM group. Among the 123 FASI cases, 107 (87%) were reported to be technically successful. The mean gestational age (GA) at diagnosis was comparable between the groups (26.2 weeks FASI vs. 24.4 weeks EM group). The mean GA at FASI was 30.4 weeks (95% CI 28.5, 32.5). The mean GA at delivery was also comparable (37.7 weeks FASI vs. 38.1 weeks EM group). Neonatal outcomes, including live birth, neonatal death, and survival to hospital discharge pooled proportions, were also comparable between groups (live birth: 92% (95% CI 64, 99) FASI versus 93% (95% CI 79, 98) in EM, neonatal death: 32% (95% CI 11, 65) FASI versus 30% (95% CI 21, 41) EM, survival to hospital discharge: 37% (95% CI 25, 52) FASI versus 52% (95% CI 42, 61) EM). Age at neonatal death was higher in the FASI group (mean: 17 days FASI vs. 7.2 days EM group). There was a lower rate of postnatal atrial restrictive septum in the FASI group 38% (95% CI 17, 63) compared to the EM group 88% (95% CI 57, 98). Our review shows variations across centers in the selection criteria and techniques used for FASI. Although survival including livebirth, neonatal death, and survival to hospital discharge did not differ between groups, the procedure may translate into a less restrictive septum at birth. Future multicenter studies are needed to better identify the subset of cases that might have improved outcomes, use standardized definitions, unified techniques, utilize core outcome set, and assess long-term benefits.

Catheter-Based Fetal Cardiac Interventions

Fetal cardiac intervention (FCI) is an emerging and rapidly advancing group of interventions designed to improve outcomes for fetuses with cardiovascular disease. Currently, FCI is comprised of pharmacologic therapies (e.g., trans-placental antiarrhythmics for fetal arrhythmia), open surgical procedures (e.g., surgical resection of pericardial teratoma), and catheter-based procedures (e.g., fetal aortic valvuloplasty for aortic stenosis). This review focuses on the rationale, criteria for inclusion, technical details, and current outcomes of the three most frequently performed catheter-based FCI procedures: (1) aortic valvuloplasty for critical aortic stenosis (AS) associated with evolving hypoplastic left heart syndrome (HLHS), (2) atrial septal intervention for HLHS with severely restrictive or intact atrial septum (R/IAS), and (3) pulmonary valvuloplasty for pulmonary atresia with intact ventricular septum (PA/IVS).

Transcatheter Palliation With Pulmonary Artery Flow Restrictors in Neonates With Congenital Heart Disease: Feasibility, Outcomes, and Comparison With a Historical Hybrid Stage 1 Cohort

BACKGROUND

Neonates with complex congenital heart disease and pulmonary overcirculation have been historically treated surgically. However, subcohorts may benefit from less invasive procedures. Data on transcatheter palliation are limited.

METHODS

We present our experience with pulmonary flow restrictors (PFRs) for palliation of neonates with congenital heart disease, including procedural feasibility, technical details, and outcomes. We then compared our subcohort of high-risk single ventricle neonates palliated with PFRs with a similar historical cohort who underwent a hybrid Stage 1. Cox regression was used to evaluate the association between palliation strategy and 6-month mortality.

RESULTS

From 2021 to 2023, 17 patients (median age, 4 days; interquartile range [IQR], 2-8; median weight, 2.5 kilograms [IQR, 2.1-3.3]) underwent a PFR procedure; 15 (88%) had single ventricle physiology; 15 (88%) were high-risk surgical candidates. All procedures were technically successful. At a median follow-up of 6.2 months (IQR, 4.0-10.8), 13 patients (76%) were successfully bridged to surgery (median time since PFR procedure, 2.6 months [IQR, 1.1-4.4]; median weight, 4.9 kilograms [IQR, 3.4-5.8]). Pulmonary arteries grew adequately for age, and devices were easily removed without complications. The all-cause mortality rate before target surgery was 24% (n=4). Compared with the historical hybrid stage 1 cohort (n=23), after adjustment for main confounding (age, weight, intact/severely restrictive atrial septum or left ventricle to coronary fistulae), the PFR procedure was associated with a significantly lower all-cause 6-month mortality risk (adjusted hazard ratio, 0.26 [95% CI, 0.08-0.82]).

CONCLUSIONS

Transcatheter palliation with PFR is feasible, safe, and represents an effective strategy for bridging high-risk neonates with congenital heart disease to surgical palliation, complete repair, or transplant while allowing for clinical stabilization and somatic growth.

Hypoplastic Left Heart Syndrome: Signaling & Molecular Perspectives, and the Road Ahead

Hypoplastic left heart syndrome (HLHS) is a lethal congenital heart disease (CHD) affecting 8-25 per 100,000 neonates globally. Clinical interventions, primarily surgical, have improved the life expectancy of the affected subjects substantially over the years. However, the etiological basis of HLHS remains fundamentally unclear to this day. Based upon the existing paradigm of studies, HLHS exhibits a multifactorial mode of etiology mediated by a complicated course of genetic and signaling cascade. This review presents a detailed outline of the HLHS phenotype, the prenatal and postnatal risks, and the signaling and molecular mechanisms driving HLHS pathogenesis. The review discusses the potential limitations and future perspectives of studies that can be undertaken to address the existing scientific gap. Mechanistic studies to explain HLHS etiology will potentially elucidate novel druggable targets and empower the development of therapeutic regimens against HLHS in the future.

Echocardiographic features and outcome of restrictive foramen ovale in fetuses with and without cardiac malformations: Literature review

Foramen ovale is a small communication between the left and the right atrium and its restriction is a rare congenital heart anomaly. There is no consensus on diagnosis and management of fetal restrictive foramen ovale (RFO). In our paper we included 11 studies about fetuses affected by isolated RFO, RFO with D-Transposition of the Great Arteries (dTGA) and RFO with hypoplastic left heart syndrome (HLHS). While fetuses affected from HLHS and dTGA with RFO have a poor prognosis, premature RFO in an otherwise structurally normal heart, if found in later gestation, have an overall good outcome.

High-Risk Anatomic Subsets in Hypoplastic Left Heart Syndrome

Despite overall improvements in outcomes for patients with hypoplastic left heart syndrome, there remain anatomic features that can place these patients at higher risk throughout their treatment course. These include severe preoperative obstruction to pulmonary venous return, restrictive atrial septum, coronary fistulae, severe tricuspid regurgitation, smaller ascending aorta diameter (especially if <2 mm), and poor ventricular function. The risk of traditional staged palliation has led to the development of alternative strategies for such patients. To further improve the outcomes, we must continue to diligently examine and study anatomic details in HLHS patients.

Hypoplastic Left Heart Syndrome Across the Lifespan: Clinical Considerations for Care of the Fetus, Child, and Adult

Hypoplastic left heart syndrome (HLHS) is the most common anatomic lesion in children born with single ventricle physiology and is characterized by the presence of a dominant right ventricle and a hypoplastic left ventricle along with small left-sided heart structures. Diagnostic subgroups of HLHS reflect the extent of inflow and outflow obstruction at the aortic and mitral valves, specifically stenosis or atresia. If left unpalliated, HLHS is a uniformly fatal lesion in infancy. Following introduction of the Norwood operation, early survival has steadily improved over the past four decades, mirroring advances in operative and peri-operative management as well as reflecting refinements in patient surveillance and interstage clinical care. Notably, survival following staged palliation has increased from 0% to a 5-year survival of 60-65% for children in some centres. Despite the prevalence of HLHS in childhood with relatively favourable surgical outcomes in contemporary series, this cohort is only now reaching early adult life and longer-term outcomes have yet to be elucidated. In this article we focus on contemporary clinical management strategies for patients with HLHS across the lifespan, from fetal to adult life. Nomenclature and diagnostic considerations are discussed and current literature pertaining to putative genetic etiologies is reviewed. The spectrum of fetal and pediatric interventional strategies, both percutaneous and surgical, are described. Clinical, patient-reported and neurodevelopmental outcomes of HLHS are delineated. Finally, note is made of current areas of clinical uncertainty and suggested directions for future research are highlighted.

Evolving Approach in Hypoplastic Left Heart Syndrome With Restrictive and Intact Septum

Background: Hypoplastic left heart syndrome (HLHS) with either intact atrial septum (IS) or highly restrictive interatrial communication (HRIC) is associated with poor survival. Immediate postpartum access to cardiac therapy and timely left atrial decompression (LAD) are paramount to a successful outcome. We describe herein our evolving approach to LAD and report interstage and longer-term results. Methods: We retrospectively identified neonates with HLHS IS/HRIC requiring LAD between 2005 and 2019. All babies had prenatal/postnatal echocardiography. Our LAD strategy evolved over time from attempt at transcatheter balloon atrial septostomy (BAS) to surgical septectomy with inflow occlusion, to hybrid trans-atrial stent implantation. Results: Twelve neonates required LAD at a median time of 14 (0.5-31) hours after birth. Five patients underwent BAS that proved successful in 2 cases. Of the 3 unsuccessful cases, 2 required extra-corporeal membrane oxygenation (ECMO) support and died subsequently; one underwent hybrid trans-atrial stent implantation. Of the remaining 7 patients, 3 underwent surgical septectomy with inflow-occlusion and 4 underwent hybrid trans-atrial stent implantations. Overall, 8 patients survived LAD and reached Norwood palliation. Three of the 8 required ECMO postoperatively. There was no hospital mortality after Norwood stage 1 palliation and interstage survival was 100%. Six patients successfully underwent Glenn shunt (superior cavopulmonary anastomosis) and 5 have completed total cavopulmonary connection. Conclusions: Our experience suggests that prompt postnatal LAD can be safely achieved with careful multidisciplinary planning and accurate antenatal diagnosis. In our hands, hybrid trans-atrial septal stent insertion appears to be a safe approach which combines the versatility of transcatheter techniques together with the effectiveness of surgical control.

Hypoplastic left heart syndrome with prenatally diagnosed foramen ovale restriction: diagnosis, management and outcome

OBJECTIVE

Despite advances in prenatal diagnosis and postnatal intervention/surgery methods, patients with Hypoplastic Left Heart Syndrome (HLHS) and coexisting foramen oval restriction still achieve high mortality rates. Our objective was to determine survival predictors and to find answers to, why restriction develops in some, but not others.

METHODS

We performed a retrospective analysis of prenatal history and postnatal sequel of 22 patients with HLHS and foramen ovale restriction between 2008 and 2017.

RESULTS

There were 11 survivors and 11 nonsurvivors. The most significant difference between the two groups pertained to the average time of foramen ovale restriction diagnosis which was 33 weeks for survivors and 28 weeks for nonsurvivors (p = .0416) and the duration of in-utero restriction (9 versus 5 weeks, p = .0213). Twenty patients (20/22) exhibited possible signs of infection.

CONCLUSIONS

(1) Earlier development and longer presence of foramen ovale restriction in the setting of HLHS is associated with higher short-term mortality regardless of the degree of restriction. (2) Ratio of forward pulmonary vein flow to reverse flow (f/r) expressed as a velocity-time integral (VTI) is a good emergent intervention predictor, but it does not correlate with foramen ovale size and maximal velocity, nor does it influence survival rates. (3) Ultrasonographic signs of possible infection of the fetus is a potential risk factor of foramen ovale restriction development in patients with HLHS.

Maternal Hyperoxygenation Testing in Fetuses with Hypoplastic Left-Heart Syndrome: Association with Postnatal Atrial Septal Restriction

INTRODUCTION

In fetuses with hypoplastic left-heart syndrome (HLHS), maternal hyperoxygenation (MHO) may aid risk stratification. We hypothesized that pulmonary vein (Pvein) velocity time integral (VTI) change with MHO would more reliably identify neonates who undergo emergent atrial septoplasty (EAS) than changes in pulmonary arterial pulsatility index (PA PI).

METHODS

Fetuses with HLHS who underwent MHO testing at our institution between 2014 and 2019 were identified. Data were reviewed in a blinded, retrospective manner. Pvein VTI ratio (prograde:retrograde) was calculated. The primary outcome was neonatal EAS.

RESULTS

Twenty-seven HLHS fetuses underwent MHO, and 5 (19%) underwent EAS. Without MHO, a Pvein VTI ratio <3 conferred 60% sensitivity and 100% specificity for EAS. With MHO, a Pvein VTI ratio <6.5 conferred 100% sensitivity and specificity. For an intermediate group of fetuses with a baseline Pvein VTI ratio 3-7, the ratio decrease with MHO conferred 100% sensitivity and specificity. Compared to the Pvein VTI ratio, PA PI was less accurate in identifying EAS neonates.

DISCUSSION/CONCLUSION

Addition of MHO appears to improve the diagnostic ability of the Pvein VTI ratio to identify HLHS fetuses who undergo EAS. The Pvein VTI ratio change may more accurately identify fetuses who undergo EAS than change in PA PI and has less interobserver variability.

Impacts of prenatal diagnosis of congenital heart diseases on outcomes

Prenatal diagnosis of congenital heart diseases (CHD) is increasingly performed in developed countries. Still, the current impacts of prenatal diagnosis on fetal and neonatal outcomes remains unclear or contradictory. We will review here the different consequences of prenatal screening and of fetal echocardiography on different categories of outcomes. Increasing detection may lead to a reduced birth incidence of severe complex CHD through a high rate of termination of pregnancy but this trend is not universal. Conversely, one of the main impacts of prenatal diagnosis is to optimize perinatal care and to improve hard outcomes such as mortality. Indeed, decrease of neonatal mortality is inconsistently observed in transposition of the great arteries and is not shown in other defects. The reduction of perinatal morbidity is a new end-point to scrutinize but how to examine this impact is controversial in the neonatal period. The influence of the reduction of neonatal distress may modify neurodevelopmental outcomes and quality of survival. The risk stratification after a prenatal diagnosis of CHD helps to optimize the timing, mode, and site of management with the aim to improve outcomes. The anticipated care is tailored according to the type of CHD and expected initial physiology. However, the imprecision of prenatal diagnosis even in expert centers hampers this logical outcome. Prediction of the type of repair is theoretically possible but remains challenging in defects such as double outlet right ventricles or pulmonary atresia with ventricular septal defect. The cost of prenatal diagnosis or of its absence is still a matter of debate and policies have to be tailored to regional health systems. Finally, the impact on parents and siblings is a rarely explored outcome. Screening and echography of fetal heart are currently performed in developed countries but it is still too early to talk about fetal cardiology.

Toward Eliminating Perinatal Comfort Care for Prenatally Diagnosed Severe Congenital Heart Defects: A Vision

Over the past 40 years, the medical and surgical management of congenital heart disease has advanced considerably. However, substantial room for improvement remains for certain lesions that have high rates of morbidity and mortality. Although most congenital cardiac conditions are well tolerated during fetal development, certain abnormalities progress in severity over the course of gestation and impair the development of other organs, such as the lungs or airways. It follows that intervention during gestation could potentially slow or reverse elements of disease progression and improve prognosis for certain congenital heart defects. In this review, we detail specific congenital cardiac lesions that may benefit from fetal intervention, some of which already have documented improved outcomes with fetal interventions, and the state-of-the-science in each of these areas. This review includes the most relevant studies from a PubMed database search from 1970 to the present using key words such as fetal cardiac, fetal intervention, fetal surgery, and EXIT procedure. Fetal intervention in congenital cardiac surgery is an exciting frontier that promises further improvement in congenital heart disease outcomes. When fetuses who can benefit from fetal intervention are identified and appropriately referred to centers of excellence in this area, patient care will improve.

Fetal Cardiac Interventions-Are They Safe for the Mothers?

The aim of fetal cardiac interventions (FCI), as other prenatal therapeutic procedures, is to bring benefit to the fetus. However, the safety of the mother is of utmost importance. The objective of our study was to evaluate the impact of FCI on maternal condition, course of pregnancy, and delivery. 113 mothers underwent intrauterine treatment of their fetuses with critical heart defects. 128 percutaneous ultrasound-guided FCI were performed and analyzed. The patients were divided into four groups according to the type of FCI: balloon aortic valvuloplasty (fBAV), balloon pulmonary valvuloplasty (fBPV), interatrial stent placement (IAS), and balloon atrioseptoplasty (BAS). Various factors: maternal parameters, perioperative data, and pregnancy complications, were analyzed. There was only one major complication—procedure-related placental abruption (without need for blood products transfusion). There were no cases of: procedure-related preterm prelabor rupture of membranes (pPROM), chorioamnionitis, wound infection, and anesthesia associated complications. Tocolysis was only necessary only in two cases, and it was effective in both. None of the patients required intensive care unit admission. The procedure was effective in treating polyhydramnios associated with fetal heart failure in six out of nine cases. Deliveries occurred at term in 89%, 54% were vaginal. The results showed that FCI had a negligible impact on a further course of pregnancy and delivery.

Late Heart Transplantation in Hypoplastic Left Heart Syndrome With Intact Atrial Septum

This case report describes 2 patients born with hypoplastic left heart syndrome and an intact atrial septum who underwent a strategy of immediate extracorporeal membrane oxygenation and left atrial decompression followed by hybrid Norwood palliation as a bridge to further palliation. Heart transplantation was ultimately performed in these 2 patients with persisting pulmonary vascular resistance abnormalities.

Outcomes in Hypoplastic Left Heart Syndrome

Hypoplastic left heart syndrome (HLHS) is a complex form of congenital heart disease defined by anatomic and functional inadequacy of the left side of the heart with nonviability of the left ventricle to perform systemic perfusion. Lethal if not treated, a strategy for survival currently is well established, with continuing improvement in outcomes over the past 30 years. Prenatal diagnosis, good newborn care, improved surgical skills, specialized postoperative care, and unique strategies for interstage monitoring all have contributed to increasing likelihood of survival. The unique life with a single right ventricle and a Fontan circulation is a focused area of investigation.

Risk stratification of patients with hypoplastic left heart syndrome and intact atrial septum using fetal MRI and echocardiography

Despite prenatal diagnosis, prenatal intervention, and immediate postnatal intervention, patients with hypoplastic left heart syndrome and intact or highly restrictive atrial septum have the highest risk for mortality. Charts for all infants diagnosed with hypoplastic left heart syndrome from 2009 to 2017 were retrospectively reviewed and compared, including pulmonary vein Doppler patterns on fetal echocardiogram and evidence of pulmonary lymphangiectasia on fetal MRI. Of the 81 newborns with hypoplastic left heart syndrome, we defined two groups. Group 1 patients had an adequate atrial septal communication (n = 69), while Group 2 met criteria for intact/restrictive septum (n = 12). No patient in Group 1 had a type C pulmonary vein Doppler pattern, while no patient in Group 2 had a type A pulmonary vein Doppler pattern. The two patients with pulmonary lymphangiectasia had type C pulmonary vein Doppler pattern and an intact atrial septum and did not survive. Survival to discharge for Group 1 was 83% compared to 58% for Group 2 (p = 0.116). Survival to stage 2 palliation was 71% for Group 1 compared to 50% for Group 2 (p = 0.186). Only 4 of the initial 12 patients from Group 2 are alive, which is an overall survival of 33%. Our experience supports previous evidence that fetal echocardiography can identify those patients with the greatest likelihood for postnatal intervention as well as those at highest risk for mortality. Fetal MRI is a novel imaging modality that may help providers separate patients at highest risk for mortality, regardless of pulmonary vein Doppler pattern.

Pulmonary venous Doppler patterns and midterm outcomes in fetuses with left-sided obstructive lesions and restrictive atrial septum

OBJECTIVE

To compare length of stay of the initial neonatal hospitalization and mortality across multiple stages of surgical palliation for infants with left-sided obstructive lesions and severely restrictive or intact atrial septum (I/RAS).

METHODS

Retrospective cohort study of patients prenatally diagnosed with left-sided obstructive lesions and I/RAS, defined by fetal pulmonary venous Dopplers.

RESULTS

We identified 76 fetal patients with 59 live born intending to pursue intervention. Those with I/RAS had longer durations of mechanical ventilation (P = .031) but no difference in intensive care unit or total length of stay. Survival to discharge from neonatal hospitalization was 41.7% in the I/RAS group and 80.7% in the unrestrictive group (P = .001). There was a higher proportion of deaths between stage 1 and stage 2 in the I/RAS group - 5/9 (55.6%) vs 9/50 (18%) in the unrestrictive group (P = .027). Beyond stage 2 palliation there was trend toward a difference in overall mortality (66.7% in I/RAS vs 35.7% in unrestrictive, P = .05) but no statistically significant difference in transplant-free survival (33.3% in I/RAS vs 53.5% in unrestrictive, P = .11).

CONCLUSION

The survival disadvantage conferred by prenatally diagnosed severe atrial septal restriction is most pronounced in the neonatal and early infancy period, with no detectable difference in late midterm transplant-free survival in our cohort.

Outcomes of hypoplastic left heart syndrome: analysis of National Inpatient Sample Database 1998-2004 versus 2005-2014

Neonates with hypoplastic left heart syndrome (HLHS) were identified from the National Inpatient Sample dataset for the years 1998-2014. These patients were stratified into two chronological groups, past group (1998-2005) and recent group (2006-2014). A total of 20,649 neonates with HLHS were identified. Of them, 9179 (44.5%) were born in the past group and 11,470 (55.5%) in the recent group. Median birth weight was significantly less in the recent group (2967 g vs. 3110 g, p = 0.005). The patients in the recent group had more patients with low birth weight ( < 2.5 kg) and prematurity (8.7% vs 7.6% and 12.7% vs. 4.3%., respectively). In addition, recent group had more comorbidities including chromosomal anomalies, total anomalous pulmonary venous return, and kidney anomalies (5.6% vs. 3.6%, 2.3% vs. 1.7%, and 5.6% vs. 3.6%, respectively, p < 0.001); these were associated with a higher rate of extracorporeal membrane oxygenation utilization (9.2% vs. 4.5%, p < 0.001). Consequently, median length of stay was longer in the recent group (8 vs. 6 days, p < 0.001).Conclusion: Despite the higher frequency of comorbidities in recent group, the mortality rates decreased by 20% (from 25.3% to 20.6%, p < 0.001). Balloon atrial septostomy was performed less frequently in the recent group (23.3% vs. 16.1%, p < 0.001).What is known:• Hypoplastic left heart syndrome has the highest mortality among congenital cardiac defects during the first year of life.• Limited studies on patients' comorbidities and mortality rates trends over last two decades.What is new:• The study utilized a national database to compare in-hospital mortality and length of stay between the two time periods 1998-2005 and 2006-2014.• The recent group had more comorbidities (prematurity, chromosomal anomalies, total anomalous pulmonary venous return, and kidney anomalies), and there was higher rate of ECMO and longer length of stay, while mortality rates decreased by 20%.

Fetal Cardiac Intervention in Critical Aortic Stenosis with Severe Mitral Regurgitation, Severe Left Atrial Enlargement, and Restrictive Foramen Ovale

OBJECTIVE

To assess the intrauterine course and outcome of fetal cardiac intervention (FCI) in fetuses with critical aortic stenosis (CAS), severe mitral regurgitation (MR), severe left atrial dilatation (LAD), and restrictive foramen ovale (RFO) or intact atrial septum.

METHODS

All fetuses with a prenatal diagnosis of CAS, severe MR, severe LAD, and RFO were retrospectively collected in one tertiary center for fetal medicine over a period of 10 years. Video recordings, pre- and postnatal charts were reviewed for cardiac and extracardiac anomalies, intrauterine course, and postnatal outcome.

RESULTS

Nineteen fetuses with CAS, severe MR, severe LAD, and RFO were diagnosed in the study period. In 5 cases, FCI was not considered as the parents either opted for expectative management or for termination. In the remaining 14 fetuses, 21 FCI were performed: 14 balloon valvuloplasties, 2 atrioseptostomies, and 5 fetal atrial stent insertions. Seven of 14 fetuses (50%) had fetal hydrops, 5 of 14 fetuses (36%) presented with intact atrial septum. Procedure-related death occurred in 5 fetuses after aortic valvuloplasty or concomitant atrioseptostomy but in none after fetal atrial stenting. Due to progressive hydrops, two terminations of pregnancy were performed. Among the 7 live births, 3 died in the neonatal period. The remaining 4 received single ventricle palliation, 2 following fetal aortic valvuloplasty and 2 after fetal atrial stent insertion.

CONCLUSIONS

CAS with severe MR, severe LAD, and RFO has a high overall mortality even in cases undergoing intrauterine intervention. Parameters that accurately predict the intrauterine and postnatal outcome have yet to be defined.

New Aspects in the Diagnosis and Therapy of Fetal Hypoplastic Left Heart Syndrome

Fetal hypoplastic left heart syndrome (HLHS) is a severe congenital heart disease with a lethal prognosis without postnatal therapeutic intervention or surgery. The aim of this article is to give a brief overview of new findings in the field of prenatal diagnosis and the therapy of HLHS. As cardiac output in HLHS children depends on the right ventricle (RV), prenatal assessment of fetal RV function is of interest to predict poor functional RV status before the RV becomes the systemic ventricle. Prenatal cardiac interventions such as fetal aortic valvuloplasty and non-invasive procedures such as maternal hyperoxygenation seem to be promising treatment options but will need to be evaluated with regard to long-term outcomes. Novel approaches such as stem cell therapy or neuroprotection provide important clues about the complexity of the disease. New aspects in diagnostics and therapy of HLHS show the potential of a targeted prenatal treatment planning. This could be used to optimize parental counseling as well as pre- and postnatal management of affected children.

Fetal interventions for structural heart disease

Fetal cardiac intervention (FCI) offers the potential to alter in utero anatomy and physiology. For aortic stenosis with evolving hypoplastic left heart syndrome and pulmonary atresia with intact ventricular septum with evolving hypoplastic right heart syndrome, FCI may result in maintenance of a biventricular circulation, thus avoiding single-ventricle palliation and its attendant complications. In the case of hypoplastic left heart syndrome with intact atrial septum, FCI may ameliorate in utero pathophysiology and portend a more favorable postnatal prognosis. In all cases, a detailed fetal echocardiographic assessment to identify the appropriate FCI candidate is essential. This article reviews the three aforementioned lesions for which FCI can be considered. The pathophysiology and rationale for intervention, echocardiographic assessment, patient selection criteria, and outcomes for each lesion will be reviewed. A primary focus will be the echocardiographic evaluation of each lesion.

Echocardiographic predictors of neonatal illness severity in fetuses with critical left heart obstruction with intact or restrictive atrial septum

BACKGROUND

Neonates with critical left heart obstruction and intact atrial septum (IAS) or restrictive atrial septum (RAS) are at risk for hypoxia within hours of birth and remain a group at high risk for mortality.

METHODS

Prenatally diagnosed fetuses with critical left heart obstruction and IAS or RAS with follow-up from January 1, 2005, to February 14, 2017, were included. Primary outcome was a composite measure of severe neonatal illness (pH < 7.15, venous pH < 7.10, bicarbonate < 16 mmol/L, lactic acid > 5 mmol/L, or median oxygen saturation < 60% within 2 hours of birth).

RESULTS

Of 68 live born fetuses, 52 (76.5%) had hypoplastic left heart syndrome, 14 (20.5%) had critical aortic stenosis, and two (3%) had complex anatomy with mitral stenosis/atresia. There were 27 (39.7%) fetuses with IAS and 41 (60.3%) with RAS. Severe neonatal illness was present in 36 (52.9%). The strongest discriminators for severe neonatal illness were a pulmonary vein A:R VTI ≤ 2.7 (P < 0.001, AUC 0.93) and larger pulmonary vein diameter (P = 0.025, AUC 0.77). A:R VTI ≤ 2.7 predicted death or transplant (log-rank P = 0.03).

CONCLUSIONS

In neonates with hypoplastic left heart syndrome and IAS or RAS, A:R VTI ≤ 2.7 is predictive of severe neonatal instability. This threshold can help guide resource planning, delivery management, and improve fetal intervention criteria.

Prenatal therapy for fetal cardiac disorders

Fetal cardiac abnormalities are some of the commonest congenital disorders seen in prenatal life. They can be anatomical or functional and can develop de novo or as a consequence of either maternal or fetal disease. Untreated, morbidity and mortality rates are high for hypoplastic left heart disorders and for some fetal tachy and bradyarrhythmias. Optimum management strategies are often not clear because of the lack of knowledge about the precise natural history of some of these conditions. Prenatal therapy ranges from invasive fetal cardiac intervention to maternal administration of drugs for transplacental transfer to the fetus. This comprehensive review covers many fetal cardiac disorders and various prenatal therapeutic options that are available.

A potentially curative fetal intervention for hypoplastic left heart syndrome

Hypoplastic left heart syndrome (HLHS) encapsulates a spectrum of complex congenital cardiovascular malformations involving varying degrees of underdevelopment of the left-sided heart structures. However, despite improved survival rates since the introduction of staged surgical reconstruction, treatment options for HLHS remain palliative rather than curative. A major limiting factor in the development of definitive curative therapy for HLHS is an incomplete understanding of its pathogenesis. Currently, the aetiology HLHS is best conceptualised by the 'flow theory' of cardiogenesis, which states that normal cardiac development is reliant on the interrelationship of normal flow patterns of blood through the developing heart, and appropriate growth of the cardiac valves and myocardium. Thus, congenital cardiac malformations, such as HLHS, are thought to arise when these two processes are incorrectly coupled in utero. The rationale for the hypothesis proposed herein rests upon the flow theory of cardiogenesis. Morphological studies of HLHS indicate that, although underdeveloped, all left-sided cardiac structures are present and anatomically correct. Further, of the various structural abnormalities that can occur within the spectrum of HLHS, the presence of a ventricular septal defect (VSD) is rare. The rarity of a VSD within the morphological spectrum of HLHS suggests the syndrome may not develop in the presence of a functionally significant VSD. Presumably, the presence of a functional VSD establishes a communication between the two ventricles during cardiac development, and preserves the normal pressure-flow-dependent growth of the left ventricular (LV) myocardium, despite inflow/outflow valve defects. It is proposed that surgical creation of a VSD in utero will 'rescue' the LV of hearts with left-sided valvular deformities that render them susceptible to the development of HLHS later in gestation. In evaluating this hypothesis, potential techniques for surgical creation of a VSD in utero are offered. These techniques are based on already established catheter-based in utero interventions, and conventional postnatal percutaneous procedures for VSD creation. Further discussion is also offered on techniques to avoid, and manage, potential complications (i.e. conduction system damage) of the proposed technique(s). Finally, if VSD creation in utero is indeed practically feasible, and successfully establishes the hypothesised hemodynamic and myocardial growth normalisation within the abnormally developing LV, the clinical implications are profound. This procedure may hold a potential cure for almost every sub-type of HLHS.

The boundaries of fetal cardiac intervention: Expand or tighten?

Fetal cardiac intervention (FCI) is a relatively new and continually evolving field, and, for select cardiac defects, offers the potential to alter the progression of the disease and improve outcomes. It is a procedure that requires a collaborative effort between maternal-fetal medicine, interventional cardiology and fetal echo/ultrasound specialists, as well as fetal and maternal anesthesiologists, nursing specialists, and social workers. This article reviews the most recently reported data and advances in FCI. Currently, FCI is most frequently performed in fetuses with severe aortic stenosis (AS) with evolving hypoplastic left heart syndrome (eHLHS), established HLHS with intact or highly restrictive atrial septum (IAS), and pulmonary atresia with intact ventricular septum (PA-IVS) with evolving hypoplastic right heart syndrome (eHRHS). The goal of FCI for eHLHS and eHRHS is to promote a postnatal biventricular circulation with, theoretically, the potential for better long-term outcomes. In HLHS with IAS the aim is to improve survival. Contemporary data for FCI demonstrate limited maternal risks and improving technical success. With experience, FCI in severe AS with eHLHS has shown improved rates of biventricular outcome and early survival. Limited data for PA-IVS show promise for improving postnatal biventricular outcomes; however, for HLHS with IAS, FCI has yet to clearly demonstrate improved survival. FCI has an evolving role in the management of congenital heart defects. Ongoing analysis of disease progression, patient selection and postnatal outcomes, in conjuncture with technologic innovations and a multicenter collaborative approach, is essential as the field expands.

Assessing the impact of total extracorporeal circulation on hemodynamics in an ovine fetal model

The present study aimed to evaluate the impact of total extracorporeal circulation on hemodynamics and placental function in an ovine fetal model. Mid-term ovine fetuses (n=6) underwent extracorporeal circulation (30 min), cardioplegic arrest (20 min) and monitoring (120 min). The ascending aorta and umbilical cords of the fetuses were occluded during the bypass and an extracorporeal membrane oxygenator was used as the oxygen source. Biventricular intracardiac pressures, echocardiographic data, blood gas levels and placental function variables were recorded, and statistical analysis was performed using the repeated-measure analysis of variance test. The data indicated that fetal heart rate and blood pressure at 30, 60, 90 and 120 min following the bypass were stable relative to pre-arrest baseline (pre-bypass) values (P>0.05). However, end diastolic pressures in the ovine right ventricles post-bypass were significantly increased at 30, 60, 90 and 120 min relative to pre-bypass pressures (P<0.05). The pulsatility index also increased at 30 min post-bypass relative to the pre-bypass score (0.91±0.06 vs. 0.61±0.14; P=0.007). The mean resistivity index at all time points post-bypass was consistent with the pre-bypass score (P>0.05), while the mean Tei index values for the left and right ventricles post-bypass were significantly higher at all time points relative to pre-bypass values (P<0.05). The pre-bypass fetal blood pH, SaO₂, base excess and lactate values were maintained during arrest (P>0.05). Fetal hemodynamics and placental function additionally remained stable for up to 2 h upon reperfusion following total extracorporeal circulation and cardioplegic arrest. Collectively these data suggest that the reproducible ovine fetal model may be useful in the evaluation of fetal cardiac surgery.

Congenital pulmonary lymphangiectasia and early mortality after stage 1 reconstruction procedures

OBJECTIVES

Pulmonary lymphangiectasia associated with hypoplastic left heart syndrome with an intact or restrictive atrial septum may result from increased left atrial pressure, and is associated with worse outcomes following staged reconstruction due to lung dysfunction and significant hypoxaemia. Our objective was to characterise the incidence of pulmonary lymphangiectasia in cases of early mortality following stage 1 reconstructions.

METHODS

An institutional cardiac surgical database was retrospectively searched for patients who died within 30 days following a stage 1 reconstruction between 1 January, 1984 and 31 December, 2013. During that period, 1669 stage 1 procedures were performed. Autopsy lung specimens were reviewed by a paediatric pathologist. Patients who died of suspected technical issues were excluded.

RESULTS

A total of 54 patients were included, and of these seven cases (8.5%) of pulmonary lymphangiectasia were identified. The mean estimated gestational age was 38.2±2.4 weeks, and the mean birth weight was 3.0±0.6 kg. The median interval between surgery and death was 1 day (with a range from 0 to 18 days). The atrial septum was intact in one patient (14.3%), restrictive in three patients (42.9%), and unrestrictive in three patients (42.9%).

CONCLUSIONS

Pulmonary lymphangiectasia may develop in hypoplastic left heart syndrome with or without a restrictive atrial septum. As standard prenatal diagnostic evaluations and treatment methods for pulmonary lymphangiectasia are limited, this may be an important contributor to early and late mortality following stage 1 reconstruction for hypoplastic left heart syndrome.

Neonatal management and outcomes of prenatally diagnosed CHDs

OBJECTIVES

The aim of this study was to determine the probability of intervention at birth after prenatal diagnosis of CHD.

METHODS

A 10-year retrospective study including all foetuses with a prenatally diagnosed CHD and those delivered in a tertiary-care cardiac centre between January, 2002 and December, 2011 was carried out. Patients were classified into eight groups according to the anticipated risk of neonatal intervention.

RESULTS

The need for urgent intervention and/or PGE1 infusion within the first 48 hours of life was 47% (n=507/1080): 72% (n=248) for CHD at risk for a Rashkind procedure, 77% (n=72) for CHD with ductal-dependent pulmonary flow, 13% (n=22) for CHD with potentially ductal-dependent pulmonary flow, 94% (n=62) for CHD with ductal-dependent systemic flow, 29% (n=88) for CHD with potentially ductal-dependant systemic flow, 50% (n=4) for total anomalous pulmonary venous connection, and 17% (n=1) for CHD with atrio-ventricular block. In all, 34% of the patients received PGE1 infusion and 21.4% underwent urgent catheter-based or surgical interventions; 10% of patients without anticipated risk (n=10) underwent an early intervention; 6.7% (n=73) of the patients died; and 55% (n=589) had an intervention before discharge from hospital.

CONCLUSION

Half of the neonates with foetal CHD benefited from an urgent intervention or PGE1 infusion at birth. We recommend scheduled delivery and in utero transfer for transposition of the great arteries, double-outlet right ventricle with sub-pulmonary ventricular septal defect, total anomalous pulmonary venous connection, CHD with atrio-ventricular block with heart rate <50, all ductal-dependant lesions, and CHD with potentially ductal-dependant systemic flow.

Efficacy of prenatal diagnosis of major congenital heart disease on perinatal management and perioperative mortality: a meta-analysis

BACKGROUND

There is no consensus on the effectiveness of prenatal diagnosis except for hospitalized outcomes. Hence, a meta-analysis of published literature was conducted to assess the effect of prenatal diagnosis.

METHODS

Literature review has identified relevant studies up to December 2013. A meta-analysis was performed according to the guidelines from the Cochrane review group and the PRISMA statement. Studies were identified by searching PubMed, Embase, the Cochrane Central Register of Controlled Trials and World Health Orgnization clinical trials registry center. Meta-analysis was performed in a fixed/random-effect model using Revman 5.1.1 according to the guidelines from the Cochrane review group and the PRISMA guidelines.

RESULTS

The results from 13 cohort studies in 12 articles were analyzed to determine the optimal treatment with the lower rate of perioperative mortality in prenatal diagnosis. The superiority of a prenatal diagnosis has been proven because the surgical procedure could be done in the early neonatal period (95% CI, -0.76, -0.40). The prenatal diagnosis has also remarkably reduced the preoperative and postoperative mortality rates in cases of transposition of the great arteries (95% CI=0.06, 0.80; 95% CI=0.01, 0.82, respectively), as well as the overall results with all subtypes (95% CI=0.18, 0.94; 95% CI=0.46, 0.94, respectively).

CONCLUSIONS

Prenatal diagnosis is effective in perinatal management with an earlier intervention for major congenital heart disease, but only results in a reduced perioperative mortality in cases of transposition of the great arteries. Further investigations are required to evaluate the effect of prenatal diagnosis on life quality during a long-term follow-up.

Fetal cardiology: changing the definition of critical heart disease in the newborn

Infants born with congenital heart disease (CHD) may require emergent treatment in the newborn period. These infants are likely to benefit the most from a prenatal diagnosis, which allows for optimal perinatal planning. Several cardiac centers have created guidelines for the management of these high-risk patients with CHD. This paper will review and compare several prenatal CHD classification systems with a particular focus on the most critical forms of CHD in the fetus and newborn. A contemporary definition of critical CHD is one which requires urgent intervention in the first 24 h of life to prevent death. Such cardiac interventions may be not only life saving for the infant but also decrease subsequent morbidity. Critical CHD cases may require delivery at specialized centers that can provide perinatal, obstetric, cardiology and cardiothoracic surgery care. Fetuses diagnosed in mid-gestation require detailed fetal diagnostics and serial monitoring during the prenatal period, in order to assess for ongoing changes and identify progression to a more severe cardiac status. Critical CHD may progress in utero and there is still much to be learned about how to best predict those who will require urgent neonatal interventions. Despite improved therapeutic capabilities, newborns with critical CHD continue to have significant morbidity and mortality due to compromise that begins in the delivery room. Fetal echocardiography is the best way to predict the need for specialized care at birth to improve outcome. Once the diagnosis is made of critical CHD, delivery at the proper time and in appropriate institution with specific care protocols should be initiated. More work needs to be done to better delineate the risk factors for progression of critical CHD and to determine which newborns will require specialized care. The most frequently described forms of critical CHD requiring immediate intervention include hypoplastic left heart syndrome with intact or severely restricted atrial septum, obstructed total anomalous pulmonary venous return and transposition of the great arteries with restrictive atrial septum.

Management of congenital diaphragmatic hernia with transposition of the great arteries

Congenital diaphragmatic hernia (CDH) is a relatively rare malformation, but it has a high mortality rate. Its association with congenital heart disease lowers survival rate due to severe acidosis and desaturation caused by persistent pulmonary hypertension of the neonate. We describe herein a case of CDH with transposition of the great arteries and intact ventricular septum, in a patient who was prenatally diagnosed, managed with extracorporeal oxygenation (ECMO) support and successfully treated with both CDH repair and Jatene procedure, with no respiratory or circulatory sequelae. In conclusion, precise prenatal estimation is essential, and ECMO is a useful therapeutic option in these complex cases.

Validation of a Simple Score to Determine Risk of Hospital Mortality After the Norwood Procedure

The ability to quantify patient-specific hospital mortality risk before the Norwood procedure remains elusive. This study aimed to develop an accurate and clinically feasible score to assess the risk of hospital mortality in neonates undergoing the Norwood procedure. All patients (n = 549) in the publically available Pediatric Heart Network Single Ventricle Reconstruction trial database were included in the analysis. Patients were randomly divided into a derivation (75%) and validation (25%) cohort. Preoperative factors found to be associated with mortality upon univariable analysis (P < 0.2) were included in the logistic regression model. The score was derived by including variables independently associated with mortality (P < 0.05). A 20-point score using 6 variables (birth weight, clinical syndrome or abnormal karyotype, surgeon Norwood volume or year, anatomic subtype, ascending aorta size, and obstructed pulmonary venous return) was developed using relative magnitudes of the covariates׳ odds ratio. The score was then tested in the validation cohort. In weighted regression analysis, model predicted risk of mortality correlated closely with actual rates of mortality in the derivation (R² = 0.87, P < 0.01) and validation cohorts (R² = 0.82, P < 0.01). Patients were classified as low (score: 0-5), medium (6-10), or high risk (>10). Mortality differed significantly between risk groups in both the derivation (6% vs 22% vs 77%, P < 0.01) and validation (4% vs 30% vs 53%, P < 0.01) cohorts. This mortality score is accurate in determining risk of hospital mortality in neonates undergoing planned Norwood operations. The score has the potential to be used in clinical practice to aid in risk assessment before surgery. Clinical trial registration URL: http://www.clinicaltrials.gov. Unique identifier: NCT00115934.

Hypoplastic left heart syndrome and the nutmeg lung pattern in utero: a cause and effect relationship or prognostic indicator?

BACKGROUND

Hypoplastic left heart syndrome (HLHS) is the third most common cause of critical congenital heart disease in newborns, and one of the most challenging forms to treat. Secondary pulmonary lymphangiectasia has been recognized in association with HLHS, an appearance described on fetal MRI as the "nutmeg lung."

OBJECTIVE

To investigate the association of fetal nutmeg lung with HLHS survival.

MATERIALS AND METHODS

A retrospective search of the fetal MRI database was performed. The nutmeg lung pattern was defined as T2 heterogeneous signal with tubular structures radiating peripherally from the hila. Postnatal echocardiograms and charts were reviewed.

RESULTS

Forty-four fetal MR studies met inclusion criteria, of which 4 patients (9%) had the nutmeg lung pattern and 3 of whom also had restrictive lesions. Mortality in this nutmeg lung group was 100% by 5 months of age. Of the 40 patients without nutmeg lung, mortality/orthotopic heart transplant (OHT) was 35%. Of these 40 patients without nutmeg lung, 5 had restriction on echo, 3 of whom died/had OHT before 5 months of age (60% of patients with restriction and non-nutmeg lung). There was a significantly higher incidence of restrictive lesions (P = 0.02) and mortality/OHT (P = 0.02) in patients with nutmeg lung compared to those without.

CONCLUSION

The nutmeg lung MR appearance in HLHS fetuses is associated with increased mortality/OHT (100% in the first 5 months of life compared to 35% with HLHS alone). Not all patients with restrictive lesions develop nutmeg lung, and outcome is not as poor when restriction is present in isolation. Dedicated evaluation for nutmeg lung pattern on fetal MR studies may be useful to guide prognostication and aid clinicians in counseling parents of fetuses with HLHS.

Fetal interventions for congenital heart disease

PURPOSE OF REVIEW

This article discusses the rationale, patient selection, technical aspects, and outcomes of percutaneous, ultrasound-guided fetal cardiac intervention (FCI) for structural congenital heart disease.

RECENT FINDINGS

FCI is most commonly performed for three forms of congenital heart disease: severe aortic stenosis with evolving hypoplastic left heart syndrome (HLHS), pulmonary atresia with intact ventricular septum and evolving hypoplastic right heart syndrome, and HLHS with intact or highly restrictive atrial septum. For severe aortic stenosis and pulmonary atresia with intact ventricular septum, the goal of intervention is to alter the natural history such that a biventricular circulation may be achieved postnatally. A growing number of patients have achieved a biventricular circulation; however, patient selection and postnatal management strategy are essential for success. HLHS with intact or highly restrictive atrial septum is one of the most lethal forms of congenital heart disease, and the goal of FCI is to improve survival. Although the creation of an atrial communication in utero is technically feasible and may permit greater stability in the immediate postnatal period, significant improvements in survival have not yet been reported.

SUMMARY

FCI is an evolving form of treatment for congenital heart disease that holds promise for select patients. Critical evaluation of both short and long-term outcomes is warranted.

Preoperative Stabilization of Infants With Hypoplastic Left Heart Syndrome Before Stage I Palliation

Hypoplastic left heart syndrome is a severe form of congenital heart disease that results in single-ventricle physiology. Although surgical palliation in infants with this syndrome is widely agreed on in practice, variation occurs in both surgical and medical management. Perinatal factors that affect preoperative management include the subtype of the syndrome and the patient’s birth weight, gestational age, and genetic abnormalities. The general aspects of perioperative stabilization and management are monitoring, use of vasoactive infusions, ventilatory support, and nutrition. Management strategies for balancing single-ventricle physiology are aimed at addressing the 3 major causes of desaturation: diminished pulmonary blood flow, low mixed venous oxygen saturation, and pulmonary venous desaturation.