In-utero intervention for hypoplastic left heart syndrome--a perinatologist's perspective

Transforming congenital heart disease management: Advances in fetal cardiac interventions

This review addresses the transformative advancements in fetal cardiac interventions (FCI) for congenital heart diseases (CHD), with a particular focus on aortic stenosis with evolving hypoplastic left heart syndrome, pulmonary atresia with an intact ventricular septum, and HLHS with an intact atrial septum (HLHS-IAS). We outline the specific FCI techniques employed, the refined criteria for selecting appropriate fetal and maternal candidates, and the promising yet varied outcomes associated with these procedures. Procedural strategies and clinical decision-making are examined as we take into account the fetal pathophysiology and the benefits and risks of early intervention. We highlight the role of multidisciplinary teams in improving technical success and managing immediate procedural complications, which have led to significant improvements in procedural outcomes. Additionally, the review discusses the long-term outcomes, challenges, and future research directions in FCI, emphasizing the necessity for continuous innovation and collaboration across specialties to advance the management of CHD. The integration of new technologies and research findings holds the promise of further enhancing FCI success rates and patient outcomes.

Right ventricle in hypoplastic left heart syndrome exhibits altered hemodynamics in the human fetus

Hypoplastic left heart syndrome (HLHS) represents approximately 9% of all congenital heart defects and is one of the most complex, with the left side of the heart being generally underdeveloped. Numerous studies demonstrate that intracardiac fluid flow patterns in the embryonic and fetal circulation can impact cardiac structural formation and remodeling. This highlights the importance of quantifying the altered hemodynamic environment in congenital heart defects, like HLHS, relative to a normal heart as it relates to cardiac development. Therefore, to study human cardiovascular fetal flow, computational fluid dynamic simulations were performed using 4D patient-specific ultrasound scans in normal and HLHS hearts. In these simulations, we find that the HLHS right ventricle exhibits a greater cardiac output than normal; yet, hemodynamics are relatively similar between normal and HLHS right ventricles. Overall, this study provides detailed quantitative flow patterns for HLHS, which has the potential to guide future prevention and therapeutic interventions, while more immediately providing additional functional detail to cardiologists to aid in decision making.

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.

Calcium signaling regulates ventricular hypertrophy during development independent of contraction or blood flow

In utero interventions aimed at restoring left ventricular hemodynamic forces in fetuses with prenatally diagnosed hypoplastic left heart syndrome failed to stimulate ventricular myocardial growth during gestation, suggesting chamber growth during development may not rely upon fluid forces. We therefore hypothesized that ventricular hypertrophy during development may depend upon fundamental Ca(2+)-dependent growth pathways that function independent of hemodynamic forces. To test this hypothesis, zebrafish embryos were treated with inhibitors or activators of Ca(2+) signaling in the presence or absence of contraction during the period of chamber development. Abolishment of contractile function alone in the setting of preserved Ca(2+) signaling did not impair ventricular hypertrophy. In contrast, inhibition of L-type voltage-gated Ca(2+) influx abolished contraction and led to reduced ventricular hypertrophy, whereas increasing L-type voltage-gated Ca(2+) influx led to enhanced ventricular hypertrophy in either the presence or absence of contraction. Similarly, inhibition of the downstream Ca(2+)-sensitive phosphatase calcineurin, a known regulator of adult cardiac hypertrophy, led to reduced ventricular hypertrophy in the presence or absence of contraction, whereas hypertrophy was rescued in the absence of L-type voltage-gated Ca(2+) influx and contraction by expression of a constitutively active calcineurin. These data suggest that ventricular cardiomyocyte hypertrophy during chamber formation is dependent upon Ca(2+) signaling pathways that are unaffected by heart function or hemodynamic forces. Disruption of Ca(2+)-dependent hypertrophy during heart development may therefore represent one mechanism for impaired chamber formation that is not related to impaired blood flow.

Cardiovascular magnetic resonance parameters associated with early transplant-free survival in children with small left hearts following conversion from a univentricular to biventricular circulation

BACKGROUND

We sought to identify cardiovascular magnetic resonance (CMR) parameters associated with successful univentricular to biventricular conversion in patients with small left hearts.

METHODS

Patients with small left heart structures and a univentricular circulation who underwent CMR prior to biventricular conversion were retrospectively identified and divided into 2 anatomic groups: 1) borderline hypoplastic left heart structures (BHLHS), and 2) right-dominant atrioventricular canal (RDAVC). The primary outcome variable was transplant-free survival with a biventricular circulation.

RESULTS

In the BHLHS group (n = 22), 16 patients (73%) survived with a biventricular circulation over a median follow-up of 40 months (4-84). Survival was associated with a larger CMR left ventricular (LV) end-diastolic volume (EDV) (p = 0.001), higher LV-to-right ventricle (RV) stroke volume ratio (p < 0.001), and higher mitral-to-tricuspid inflow ratio (p = 0.04). For predicting biventricular survival, the addition of CMR threshold values to echocardiographic LV EDV improved sensitivity from 75% to 93% while maintaining specificity at 100%. In the RDAVC group (n = 10), 9 patients (90%) survived with a biventricular circulation over a median follow-up of 29 months (3-51). The minimum CMR values were a LV EDV of 22 ml/m² and a LV-to-RV stroke volume ratio of 0.19.

CONCLUSIONS

In BHLHS patients, a larger LV EDV, LV-to-RV stroke volume ratio, and mitral-to-tricuspid inflow ratio were associated with successful biventricular conversion. The addition of CMR parameters to echocardiographic measurements improved the sensitivity for predicting successful conversion. In RDAVC patients, the high success rate precluded discriminant analysis, but a range of CMR parameters permitting biventricular conversion were identified.

Model of magnetically guided fetal cardiac intervention: potential to avoid direct cardiac puncture

OBJECTIVE

Fetal cardiac interventions are performed via direct cardiac puncture and are associated with significant fetal morbidity. The feasibility of utilizing magnetic navigation to maneuver a guide wire and balloon across a fetal aortic valve without direct cardiac puncture is tested.

METHODS

A fetal heart model was manufactured and placed in a catheterization laboratory equipped with magnetic navigation. Magnetically steerable guide wires along with commercially available coronary balloons were inserted into the model at a site mimicking a hepatic vein.

RESULTS

Passage of the wire and balloon was achieved on every attempt. The model was suitable for testing although the structural characteristics of the model made wire passage from the right to the left atrium the most challenging aspect. Once the wire was positioned in the left ventricle, it was easily maneuvered 180 degrees towards the left ventricular outflow tract and then the descending aorta. Advancement of a coronary balloon over this wire was uncomplicated.

CONCLUSION

In a fetal heart model, it is feasible to deliver a wire and balloon from abdominal venous access antegrade across the aortic valve. Progression to fetal lamb models is planned and may advance fetal cardiac interventions by reduction of fetal morbidity.

Future Directions of Fetal Interventions in Congenital Heart Disease

Fetal interventions for congenital heart disease have become important treatment modalities in the past 10 to 15 years. The basic hypothesis has been that a prenatal intervention may remodel cardiac morphology and function to such an extent that it may favorably alter the in utero natural history, resulting in improved prenatal and postnatal outcomes, including an increased likelihood of achieving biventricular circulation. This review discusses the current indications, techniques, and outcomes of fetal cardiac interventions and provides a glimpse into the future with regard to technical improvements and newer treatment modalities, such as maternal oxygenation and in utero pacemaker implantation.

Fluid dynamics of heart development

The morphology, muscle mechanics, fluid dynamics, conduction properties, and molecular biology of the developing embryonic heart have received much attention in recent years due to the importance of both fluid and elastic forces in shaping the heart as well as the striking relationship between the heart's evolution and development. Although few studies have directly addressed the connection between fluid dynamics and heart development, a number of studies suggest that fluids may play a key role in morphogenic signaling. For example, fluid shear stress may trigger biochemical cascades within the endothelial cells of the developing heart that regulate chamber and valve morphogenesis. Myocardial activity generates forces on the intracardiac blood, creating pressure gradients across the cardiac wall. These pressures may also serve as epigenetic signals. In this article, the fluid dynamics of the early stages of heart development is reviewed. The relevant work in cardiac morphology, muscle mechanics, regulatory networks, and electrophysiology is also reviewed in the context of intracardial fluid dynamics.

Postnatal left ventricular diastolic function after fetal aortic valvuloplasty

Fetal aortic balloon valvuloplasty (FAV) has shown promise in altering in utero progression of aortic stenosis to hypoplastic left heart syndrome. In patients who achieve a biventricular circulation after FAV, left ventricular (LV) compliance may be impaired. Echocardiographic indexes of diastolic function were compared between patients with biventricular circulation after FAV, congenital aortic stenosis (AS), and age-matched controls. In the neonatal period, patients with FAV had similar LV, aortic, and mitral valve dimensions but more evidence of endocardial fibroelastosis than patients with AS. Patients with FAV underwent more postnatal cardiac interventions than patients with AS (p = 0.007). Mitral annular early diastolic tissue velocity (E') was lower in patients with FAV and those with AS and controls in the neonatal period and over follow-up (p <0.001). Septal E' was similar among all 3 groups in the neonatal period. In follow-up patients, with FAV had lower septal E' than patients with AS or controls (p <0.001). Early mitral inflow velocity/E' was higher in patients with FAV as neonates and at follow-up (p <0.001). Mitral inflow pulse-wave Doppler-derived indexes of diastolic function were similar between groups. In conclusion, echocardiographic evidence of LV diastolic dysfunction is common in patients with biventricular circulation after FAV and persists in short-term follow-up. LV diastolic dysfunction in this unique population may have important implications on long-term risk of left atrial and subsequent pulmonary hypertension.

Cardiac tissue engineering: implications for pediatric heart surgery

Children with severe congenital malformations, such as single-ventricle anomalies, have a daunting prognosis. Heart transplantation would be a therapeutic option but is restricted due to a lack of suitable donor organs and, even in case of successful heart transplantation, lifelong immune suppression would frequently be associated with a number of serious side effects. As an alternative to heart transplantation and classical cardiac reconstructive surgery, tissue-engineered myocardium might become available to augment hypomorphic hearts and/or provide new muscle material for complex myocardial reconstruction. These potential applications of tissue engineered myocardium will, however, impose major challenges to cardiac tissue engineers as well as heart surgeons. This review will provide an overview of available cardiac tissue-engineering technologies, discuss limitations, and speculate on a potential application of tissue-engineered heart muscle in pediatric heart surgery.

Fetal intervention for cardiac disease: the cutting edge of perinatal care

Fetal cardiac valvuloplasty has been proposed for progressive cardiac disease with a poor prognosis, such as critical aortic stenosis and pulmonary atresia with intact ventricular septum and balloon atrial septostomy for hypoplastic left heart syndrome, or simple transposition of the great arteries with closed or restrictive inter-atrial communication. It is anticipated that early rescue of ventricles or the pulmonary veins from an unfavourable environment may promote healthier ventricular and vascular growth and improve postnatal outcomes. While close collaboration between the fetal medicine specialist and perinatal cardiologist may optimize the chances of technical success, obstacles to progress include the relative rarity of suitable cases and late referral for therapy. In common with other interventions in fetal medicine, there is a learning curve, and it would benefit progress if the procedures were initially concentrated in just a few centres to enable them to develop skills and experience. Following careful evaluation, it may then be desirable to train further centres and roll out best practice models.

Revisiting animal models of aortic stenosis in the early gestation fetus

BACKGROUND

Mechanisms leading to left ventricular hypoplasia and endocardial fibroelastosis in the fetus remain unknown. Prevailing theory is that obstruction to blood flow through the left ventricle leads to elevated end-diastolic pressures, compromised myocardial perfusion, and endocardial ischemia. Fetal interventions are now being performed, based on the presumption that they would prevent such pathogenic mechanisms.

METHODS

Forty first-trimester fetal sheep (mean gestational age, 53 days) were studied. Severe fetal left ventricular outflow obstruction was created by banding the ascending aorta in 25 fetuses; 15 control fetuses underwent "sham" surgery with thoracotomy. Serial fetal echocardiography was used to assess left ventricular growth and fetal hemodynamics. Findings were correlated to morphologic and histopathologic changes, and intracardiac pressure measurements obtained from fetal cardiac catheterization.

RESULTS

Surviving banded fetuses (n = 13) had one of two phenotypes: compensatory left ventricular hypertrophy (n = 7) or noncompensatory left ventricular dilatation (n = 6) with hydrops and severe left ventricular dysfunction. All fetuses had elevated left ventricular end-diastolic pressures (mean, 21 mm Hg; range, 14 to 28 mm Hg), which correlated to the gradient across the ascending aorta (mean, 41 mm Hg; range, 28 to 73 mm Hg). In vivo echocardiography findings were incongruous with those at autopsy, and demonstrated preservation of left ventricular growth indices in all fetuses. Endocardial fibroelastosis and myocardial fibrosis were not observed in any banded fetus.

CONCLUSIONS

While early gestational obstruction to flow can compromise left ventricular function in the fetus, it does not retard normal growth. Similarly, an elevated left ventricular end-diastolic pressure is not sufficient to cause myocardial fibrosis or endocardial fibroelastosis in the fetus.

Development of hypoplastic left heart syndrome after diagnosis of aortic stenosis in the first trimester by early echocardiography

We describe a case of aortic stenosis in the first trimester that progressed to hypoplastic left heart syndrome. At 11 + 3 weeks' gestation the four-chamber view was normal but evidence of increased aortic blood velocity prompted the diagnosis of aortic outflow obstruction. At 16 + 6 weeks' gestation the left ventricle was hyperechogenic, globular and dysfunctional, suggesting the development of hypoplastic left heart syndrome. The aortic valve was small and there was no flow across the mitral or aortic valves. From 17 + 3 weeks increased reversed flow in the pulmonary veins suggested restriction of the foramen ovale. Follow-up echocardiographic examinations were performed every 2-3 weeks until delivery at term. Postnatal intervention included a Norwood I operation performed on the 5th postnatal day. We have shown the feasibility and utility of early fetal echocardiography and that a left heart obstruction diagnosed in the first trimester can progress to left heart hypoplasia during the early second trimester. This information is important for planning prenatal and perinatal management.

Changes in pulmonary venous Doppler parameters in fetal cardiac defects

OBJECTIVES

Recent observations in pediatric cardiological studies have prompted discussion on the possible role of intrauterine pulmonary venous changes in neonatal and postoperative outcome of infants with congenital heart defects. This study analyzes changes of Doppler blood flow velocity waveforms in the pulmonary veins of fetuses with different cardiac defects.

METHODS

Eighty fetuses (mean gestational age, 27 weeks) with prenatally diagnosed cardiac defects were classified into one of five groups: obstructed left atrium, other left ventricular outflow tract obstruction, right ventricular outflow tract obstruction, miscellaneous cardiac defects and total anomalous pulmonary venous drainage. Doppler examination of the pulmonary veins was performed and the time velocity integral (TVI), end-diastolic (A) velocity, and pulsatility index for veins (PIV) were compared with reference ranges.

RESULTS

Fetuses with infradiaphragmatic total anomalous pulmonary venous drainage showed a continuous Doppler flow pattern instead of the typical pulsatile waveform pattern. In fetuses with obstructed left atrium and restrictive foramen ovale, a reversed A-velocity and increased PIV were found. In five of the eight fetuses with left outflow tract obstruction but patent mitral valve, PIV was increased. In the other groups there were no obvious changes in Doppler parameters.

CONCLUSIONS

We suggest routine examination of the pulmonary veins with pulsed Doppler ultrasound in every fetus with a prenatally diagnosed heart defect. Such Doppler parameters could be used in future as cut-offs for the recently reported in-utero atrial septostomy to decompress an obstructed left atrium.