Hypoplastic Left Heart Syndrome

Fetal Echocardiography in Predicting Postnatal Outcome in Borderline Left Ventricle

OBJECTIVES

 Prenatal prediction of postnatal univentricular versus biventricular circulation in patients with borderline left ventricle (bLV) remains challenging. This study investigated prenatal fetal echocardiographic parameters and postnatal outcome of patients with a prenatally diagnosed bLV.

METHODS

 We report a retrospective study of bLV patients at four prenatal centers with a follow-up of one year. BLV was defined as z-scores of the left ventricle (LV) between -2 and -4. Single-ventricle palliation (SVP), biventricular repair (BVR), and no surgical or catheter-based intervention served as the dependent outcome. Prenatal ultrasound parameters were used as independent variables. Cut-off values from receiver operating characteristic curves (ROC) were determined for significant discrimination between outcomes.

RESULTS

 A total of 54 patients were diagnosed with bLV from 2010 to 2018. All were live births. Out of the entire cohort, 8 (15 %) received SVP, 34 (63 %) BVR, and 12 (22 %) no intervention. There was no significant difference with regard to genetic or extracardiac anomalies. There were significantly more patients with endocardial fibroelastosis (EFE) in the SVP group compared to the BVR group (80 % vs. 10 %), (p < 0.001). Apex-forming LV (100 % vs. 70 %) and lack of retrograde arch flow (20 % vs. 80 %) were associated with no intervention (p < 0.001). With respect to BVR vs. SVP, the LV sphericity index provided the highest specificity (91.7 %) using a cutoff value of ≤ 0.5.

CONCLUSION

 The majority of bLV patients maintained biventricular circulation. EFE, retrograde arch flow, and LV sphericity can be helpful parameters for counseling parents and further prospective studies can be developed.

Contractility of Induced Pluripotent Stem Cell-Cardiomyocytes With an MYH6 Head Domain Variant Associated With Hypoplastic Left Heart Syndrome

Hypoplastic left heart syndrome (HLHS) is a clinically and anatomically severe form of congenital heart disease; however, its etiology remains largely unknown. We previously demonstrated that genetic variants in the MYH6 gene are significantly associated with HLHS. Additionally, induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) from an HLHS-affected family trio (affected parent, unaffected parent, affected proband) carrying an MYH6-R443P head domain variant demonstrated dysmorphic sarcomere structure and increased compensatory MYH7 expression. Analysis of iPSC-CMs derived from the HLHS trio revealed that only beta myosin heavy chain expression was observed in CMs carrying the MYH6-R443P variant after differentiation day 15 (D15). Functional assessments performed between D20-D23 revealed that MYH6-R443P variant CMs contracted more slowly (40 ± 2 vs. 47 ± 2 contractions/min, P < 0.05), shortened less (5.6 ± 0.5 vs. 8.1 ± 0.7% of cell length, P < 0.05), and exhibited slower shortening rates (19.9 ± 1.7 vs. 28.1 ± 2.5 μm/s, P < 0.05) and relaxation rates (11.0 ± 0.9 vs. 19.7 ± 2.0 μm/s, P < 0.05). Treatment with isoproterenol had no effect on iPSC-CM mechanics. Using CRISPR/Cas9 gene editing technology, introduction of the R443P variant into the unaffected parent's iPSCs recapitulated the phenotype of the proband's iPSC-CMs, and conversely, correction of the R443P variant in the proband's iPSCs rescued the cardiomyogenic differentiation, sarcomere organization, slower contraction (P < 0.05) and decreased velocity phenotypes (P < 0.0001). This is the first report to identify that cardiac tissues from HLHS patients with MYH6 variants can exhibit sarcomere disorganization in atrial but not ventricular tissues. This new discovery was not unexpected, since MYH6 is expressed predominantly in the postnatal atria in humans. These findings demonstrate the feasibility of employing patient-derived iPSC-CMs, in combination with patient cardiac tissues, to gain mechanistic insight into how genetic variants can lead to HLHS. Results from this study suggest that decreased contractility of CMs due to sarcomere disorganization in the atria may effect hemodynamic changes preventing development of a normal left ventricle.

Successful Management of a Patient With Jacobsen Syndrome and Hypoplastic Left Heart Syndrome

Jacobsen syndrome (JS) is a rare genetic condition characterized by intellectual disability, hematologic abnormalities, and congenital heart defects. A male infant presented at birth with phenotypic findings of JS and echocardiographic findings of hypoplastic left heart syndrome (HLHS). Array comparative genomic hybridization was performed at age three days and revealed an 8.1 Mb terminal deletion on the long arm of chromosome 11, consistent with JS. At five days of age, a hybrid stage 1 procedure was performed. At age 46 days, he underwent a Norwood operation followed by bidirectional Glenn at age six months. He is presently 23 months old and doing well. With careful consideration of the individual patient and comorbidities associated with JS, we propose that at least a subset of patients with JS and HLHS can do well with staged surgical palliation.

Regional Differences in Cost and Length of Stay in Neonates with Hypoplastic Left Heart Syndrome

Hypoplastic left heart syndrome (HLHS) is a highly resource-intensive diagnosis. Geographic variation in cost and length of stay (LOS) in HLHS is not well described. Neonates diagnosed with HLHS between 2000 and 2012 were identified using the Kids' Inpatient Database. Hospitalizations were stratified into two groups: (1) birth and (2) secondary. United States regional differences in hospital charges and LOS were compared using adjusted linear regression. Of 2431 birth hospitalizations, 449 neonates (18.5%) died while inpatient and mortality rates differed by region (p = 0.02). After birth, 40.5% (n = 985) of neonates were transferred; transfers were most common in the Midwest (p < 0.0001). Adjusted average LOS was shortest in the West and longest in the South (26.1 days; 95% CI 24.0, 35.1 vs. 34.9 days; 95% CI 31.8, 38.1). Average adjusted charges were lowest in the Northeast ($324,600; 95% CI $271,400, $377,900) and highest in the West ($400,500; 95% CI $346,700, $454,300, p = 0.05). Among 1895 secondary hospitalizations, 24.9% of neonates died as inpatients, and the average adjusted LOS was shortest in the West (26.8 days; 95% CI 23.9, 29.7) and longest in the South (38.5 days; 95% CI 34.4, 42.4). Average adjusted charges were lowest in the Northeast ($326,900; 95% CI $270,700, $383,100) and highest in the South ($505,900; 95% CI $450,200, $561,500, p < 0.0001). Significant geographic variations in mortality, LOS, and hospital charges exist in care of US HLHS neonates. Reducing variation in care should remain a priority in national quality efforts in congenital heart disease.

Induced pluripotent stem cell modelling of HLHS underlines the contribution of dysfunctional NOTCH signalling to impaired cardiogenesis

Hypoplastic left heart syndrome (HLHS) is among the most severe forms of congenital heart disease. Although the consensus view is that reduced flow through the left heart during development is a key factor in the development of the condition, the molecular mechanisms leading to hypoplasia of left heart structures are unknown. We have generated induced pluripotent stem cells (iPSC) from five HLHS patients and two unaffected controls, differentiated these to cardiomyocytes and identified reproducible in vitro cellular and functional correlates of the HLHS phenotype. Our data indicate that HLHS-iPSC have a reduced ability to give rise to mesodermal, cardiac progenitors and mature cardiomyocytes and an enhanced ability to differentiate to smooth muscle cells. HLHS-iPSC-derived cardiomyocytes are characterised by a lower beating rate, disorganised sarcomeres and sarcoplasmic reticulum and a blunted response to isoprenaline. Whole exome sequencing of HLHS fibroblasts identified deleterious variants in NOTCH receptors and other genes involved in the NOTCH signalling pathway. Our data indicate that the expression of NOTCH receptors was significantly downregulated in HLHS-iPSC-derived cardiomyocytes alongside NOTCH target genes confirming downregulation of NOTCH signalling activity. Activation of NOTCH signalling via addition of Jagged peptide ligand during the differentiation of HLHS-iPSC restored their cardiomyocyte differentiation capacity and beating rate and suppressed the smooth muscle cell formation. Together, our data provide firm evidence for involvement of NOTCH signalling in HLHS pathogenesis, reveal novel genetic insights important for HLHS pathology and shed new insights into the role of this pathway during human cardiac development.

Hypoplastic Left Heart Syndrome Sequencing Reveals a Novel NOTCH1 Mutation in a Family with Single Ventricle Defects

Hypoplastic left heart syndrome (HLHS) has been associated with germline mutations in 12 candidate genes and a recurrent somatic mutation in HAND1 gene. Using targeted and whole exome sequencing (WES) of heart tissue samples from HLHS patients, we sought to estimate the prevalence of somatic and germline mutations associated with HLHS. We performed Sanger sequencing of the HAND1 gene on 14 ventricular (9 LV and 5 RV) samples obtained from HLHS patients, and WES of 4 LV, 2 aortic, and 4 matched PBMC samples, analyzing for sequence discrepancy. We also screened for mutations in the 12 candidate genes implicated in HLHS. We found no somatic mutations in our HLHS cohort. However, we detected a novel germline frameshift/stop-gain mutation in NOTCH1 in a HLHS patient with a family history of both HLHS and hypoplastic right heart syndrome (HRHS). Our study, involving one of the first familial cases of single ventricle defects linked to a specific mutation, strengthens the association of NOTCH1 mutations with HLHS and suggests that the two morphologically distinct single ventricle conditions, HLHS and HRHS, may share a common molecular and cellular etiology. Finally, somatic mutations in the LV are an unlikely contributor to HLHS.

Effects of milk flow on the physiological and behavioural responses to feeding in an infant with hypoplastic left heart syndrome

Infants with hypoplastic left heart syndrome often experience difficulty with oral feeding, which contributes to growth failure, morbidity, and mortality. In response to feeding difficulty, clinicians often change the bottle nipple, and thus milk flow rate. Slow-flow nipples have been found to reduce the stress of feeding in other fragile infants, but no research has evaluated the responses of infants with hypoplastic left heart syndrome to alterations in milk flow. The purpose of this study was to evaluate the physiological and behavioural responses of an infant with hypoplastic left heart syndrome to bottle feeding with either a slow-flow (Dr. Brown's Preemie) or a standard-flow (Dr. Brown's Level 2) nipple. A single infant was studied for three feedings: two slow-flow and one standard-flow. Oral feeding, whether with a slow-flow or a standard-flow nipple, was distressing for this infant. During slow-flow feeding, she experienced more coughing events, whereas during standard-flow she experienced more gagging. Disengagement and compelling disorganisation were most common during feeding 3, that is slow-flow, which occurred 2 days after surgical placement of a gastrostomy tube. Clinically significant changes in heart rate, oxygen saturation, and respiratory rate were seen during all feedings. Heart rate was higher during standard-flow and respiratory rate was higher during slow-flow. Further research is needed to examine the responses of infants with hypoplastic left heart syndrome to oral feeding and to identify strategies that will support these fragile infants as they learn to feed. Future research should evaluate an even slower-flow nipple along with additional supportive feeding strategies.

Impact of MYH6 variants in hypoplastic left heart syndrome

Hypoplastic left heart syndrome (HLHS) is a clinically and anatomically severe form of congenital heart disease (CHD). Although prior studies suggest that HLHS has a complex genetic inheritance, its etiology remains largely unknown. The goal of this study was to characterize a risk gene in HLHS and its effect on HLHS etiology and outcome. We performed next-generation sequencing on a multigenerational family with a high prevalence of CHD/HLHS, identifying a rare variant in the α-myosin heavy chain (MYH6) gene. A case-control study of 190 unrelated HLHS subjects was then performed and compared with the 1000 Genomes Project. Damaging MYH6 variants, including novel, missense, in-frame deletion, premature stop, de novo, and compound heterozygous variants, were significantly enriched in HLHS cases (P < 1 × 10⁻⁵). Clinical outcomes analysis showed reduced transplant-free survival in HLHS subjects with damaging MYH6 variants (P < 1 × 10⁻²). Transcriptome and protein expression analyses with cardiac tissue revealed differential expression of cardiac contractility genes, notably upregulation of the β-myosin heavy chain (MYH7) gene in subjects with MYH6 variants (P < 1 × 10⁻³). We subsequently used patient-specific induced pluripotent stem cells (iPSCs) to model HLHS in vitro. Early stages of in vitro cardiomyogenesis in iPSCs derived from two unrelated HLHS families mimicked the increased expression of MYH7 observed in vivo (P < 1 × 10⁻²), while revealing defective cardiomyogenic differentiation. Rare, damaging variants in MYH6 are enriched in HLHS, affect molecular expression of contractility genes, and are predictive of poor outcome. These findings indicate that the etiology of MYH6-associated HLHS can be informed using iPSCs and suggest utility in future clinical applications.

The myocardial and coronary histopathology and pathogenesis of hypoplastic left heart syndrome

Hypoplastic left heart syndrome has the greatest mortality rate among all CHDs and without palliation is uniformly fatal. Despite noble efforts, the aetiology of this syndrome is unknown and a cure remains elusive. The genetic and anatomic heterogeneity of hypoplastic left heart syndrome supports a rethinking of old hypotheses and warrants further investigation into the histological and vascular variations recognised with this syndrome. In an effort to elucidate the pathogenesis of hypoplastic left heart syndrome, this review will focus on its unique myocardial and coronary pathology as well as evaluate the association of hypoplastic left heart syndrome with the endocardial fibroelastosis reaction.

Congenital heart disease linked to maternal autoimmunity against cardiac myosin

Structural congenital heart disease (CHD) has not previously been linked to autoimmunity. In our study, we developed an autoimmune model of structural CHD that resembles hypoplastic left heart syndrome (HLHS), a life-threatening CHD primarily affecting the left ventricle. Because cardiac myosin (CM) is a dominant autoantigen in autoimmune heart disease, we hypothesized that immunization with CM might lead to transplacental passage of maternal autoantibodies and a prenatal HLHS phenotype in exposed fetuses. Elevated anti-CM autoantibodies in maternal and fetal sera, as well as IgG reactivity in fetal myocardium, were correlated with structural CHD that included diminished left ventricular cavity dimensions in the affected progeny. Further, fetuses that developed a marked HLHS phenotype had elevated serum titers of anti-β-adrenergic receptor Abs, as well as increased protein kinase A activity, suggesting a potential mechanism for the observed pathological changes. Our maternal-fetal model presents a new concept linking autoimmunity against CM and cardiomyocyte proliferation with cardinal features of HLHS. To our knowledge, this report shows the first evidence in support of a novel immune-mediated mechanism for pathogenesis of structural CHD that may have implications in its future diagnosis and treatment.

Leftward displacement of septum primum in hypoplastic left heart syndrome

Embryologic development of atrial septum primum antedates formation of the atrioventricular and semilunar valves. Leftward displacement of the superior attachment of septum primum (LDSP) has only been described in hypoplastic left heart syndrome (HLHS). This study reports the frequency of LDSP in HLHS and correlates LDSP with other echocardiographic features of HLHS. Preoperative echocardiograms for 72 consecutive patients with classic HLHS from 1996 to 2002 at Children's Hospital of Wisconsin were reviewed. One patient was excluded for inadequate imaging. Data for the 71 patients included the following: size, location, and Doppler gradient across the atrial septal defect (ASD); location of attachment of septum primum; size and patency of the aortic valve (AoV) annulus; size and patency of the mitral valve (MV) annulus; ascending aorta diameter (AAD); and left-ventricular end diastolic dimension (LVEDD). Patients were categorized into three groups: aortic atresia/mitral atresia (AA/MA), aortic atresia/mitral stenosis (AA/MS), and aortic stenosis/mitral stenosis (AS/MS). LDSP was seen in 46 of 71 patients (64 %). By diagnostic group, 32 of 35 patients with AA/MA had LDSP (91 %) compared with 10 of 19 AA/MS patients (53 %) and 4 of 17 AS/MS patients (24 %), p < 0.05. AoV patency was seen in 4 of 46 (9 %) patients with LDSP compared with 13 of 25 (52 %) patients with normal atrial attachment, p < 0.005. Mean left heart dimensions in infants with LDSP compared with normal attachment were as follows: AoV annulus 2.24 versus 3.83 mm, AAD 2.34 versus 4.1 mm, MV annulus 3.21 versus 6.48 mm, and LVEDD 6.38 versus 13.83 mm. By two-way analysis of variance of diagnostic category versus atrial septal attachment with interaction, MV annulus and AAD were independently predicted smaller by LDSP versus normal atrial attachment, p < 0.05. Nonsignificant factors included AoV annulus, LVEDD, ASD size, and Doppler gradient. LDSP correlates with more severe maldevelopment of the left heart in patients with HLHS. Because formation of septum primum precedes development and growth of the intracardiac valves, we speculate that LDSP may be an initiating event in the development of HLHS. In addition, prenatal identification of LDSP may help direct planning of potential in utero therapies.

Antenatal corrective cardiac surgery: An emerging area for technological innovation

The possibility of intervening in utero on certain cardiac malformations with the intent to prevent secondary major alterations in structure and function is becoming a reality. Central to progress in this area is the development of instrumentation specifically designed for minimally invasive cardiac surgery in the fetus. The present review introduces a novel set of devices for interventional cardiology, based on current knowledge and prior experience, and highlights their prospective application. In meeting this objective, particular importance is assigned to the synergic contribution of diverse disciplines, both medical and nonmedical.

Dissection of cardiovascular development and disease pathways in zebrafish

The use of animal models in medicine has contributed significantly to the development of drug treatments and surgical procedures for the last century, in particular for cardiovascular disease. In order to model human disease in an animal, an appreciation of the strengths and limitations of the system are required to interpret results and design the logical sequence of steps toward clinical translation. As the world's population ages, cardiovascular disease will become even more prominent and further progress will be essential to stave off what seems destined to become a massive public health issue. Future treatments will require the imaginative application of current models as well as the generation of new ones. In this review, we discuss the resources available for modeling cardiovascular disease in zebrafish and the varied attributes of this system. We then discuss current zebrafish disease models and their potential that has yet to be exploited.