Development Of Hypoplastic Left Heart Syndrome Research Articles

77085 Impact of MYH6 Variants on Development and Clinical Course of Hypoplastic Left Heart Syndrome

ABSTRACT IMPACT: This work represents a novel way in which genetic information can be used to improve clinical decision making as it pertains to both treatment and management of congenital heart disease. OBJECTIVES/GOALS: Our lab found that MYH6 variants are both enriched in hypoplastic left heart syndrome (HLHS) and associated with decreased cardiac transplant-free survival. To elucidate the mechanisms of MYH6 variant pathogenicity, we are assessing their impact on atrial function during HLHS development and progression. METHODS/STUDY POPULATION: We are using 2D speckle-based tracking to retrospectively evaluate echocardiograms (echos) from 51 HLHS patients, 17 with MYH6 variants and 34 matched controls. Atrial function will be assessed by myocardial strain and strain rate at seven time points, beginning at the time of the patients’ earliest prenatal echo, and ending with their last available echo before death or cardiac transplant. Early left atrial function will examine the role of MYH6 variants in the development of HLHS in vivo, while longitudinal right atrial function will be assessed in order to look for differences that could be contributing to the decreased transplant-free survival seen in MYH6 variant carriers. RESULTS/ANTICIPATED RESULTS: We hypothesize that MYH6 variants cause HLHS by impairing early left atrial (LA) contractility, resulting in altered left ventricular hemodynamics and consequent hypoplasia. We therefore expect to find diminished prenatal LA function in HLHS patients with MYH6 variants. We also hypothesize that MYH6 variants continue to impair right atrial (RA) function in surgically-reconstructed HLHS hearts, necessitating earlier transplantation. Accordingly, we expect variant carriers to exhibit lower RA function at birth versus controls. We expect differences between groups to persist over time, and possibly increase in magnitude. In HLHS patients with MYH6 variants, we anticipate declining RA function will precede right ventricular function and therefore be an early indicator of transplant need. DISCUSSION/SIGNIFICANCE OF FINDINGS: This study represents a novel way in which genetic information can inform clinical decision-making. Identifying MYH6 variants as an early cause of HLHS offers chances for intervention. Understanding long-term effects of MYH6 on right atrial function in HLHS may aid in cardiac transplant risk stratification, thus improving patient outcomes.

Model of Human Fetal Growth in Hypoplastic Left Heart Syndrome: Reduced Ventricular Growth Due to Decreased Ventricular Filling and Altered Shape.

Hypoplastic left heart syndrome (HLHS) is a congenital condition with an underdeveloped left ventricle (LV) that provides inadequate systemic blood flow postnatally. The development of HLHS is postulated to be due to altered biomechanical stimuli during gestation. Predicting LV size at birth using mid-gestation fetal echocardiography is a clinical challenge critical to prognostic counseling. We hypothesized that decreased ventricular filling in utero due to mitral stenosis may reduce LV growth in the fetal heart via mechanical growth signaling. We developed a novel finite element model of the human fetal heart in which cardiac myocyte growth rates are a function of fiber and cross-fiber strains, which is affected by altered ventricular filling, to simulate alterations in LV growth and remodeling. Model results were tested with echocardiogram measurements from normal and HLHS fetal hearts. A strain-based fetal growth model with a normal 22-week ventricular filling (1.04 mL) was able to replicate published measurements of changes between mid-gestation to birth of mean LV end-diastolic volume (EDV) (1.1-8.3 mL) and dimensions (long-axis, 18-35 mm; short-axis, 9-18 mm) within 15% root mean squared deviation error. By decreasing volumetric load (-25%) at mid-gestation in the model, which emulates mitral stenosis in utero, a 65% reduction in LV EDV and a 46% reduction in LV wall volume were predicted at birth, similar to observations in HLHS patients. In retrospective blinded case studies for HLHS, using mid-gestation echocardiographic data, the model predicted a borderline and severe hypoplastic LV, consistent with the patients' late-gestation data in both cases. Notably, the model prediction was validated by testing for changes in LV shape in the model against clinical data for each HLHS case study. Reduced ventricular filling and altered shape may lead to reduced LV growth and a hypoplastic phenotype by reducing myocardial strains that serve as a myocyte growth stimulus. The human fetal growth model presented here may lead to a clinical tool that can help predict LV size and shape at birth based on mid-gestation LV echocardiographic measurements.

Abstract 96: Epigenetic And Transcriptional Regulation Of Induced Pluripotent Stem Cells In Patients With Hypoplastic Left Heart Syndrome

Background: Although a number of studies have uncovered heterozygous mutations in cardiac regulatory genes caused hypoplastic left heart syndrome (HLHS), the identified genetic variants may not be directly correlated with the disease development. The aim of this study is to determine the epigenetic and transcriptional network responsible for myocardial patterning and morphogenesis during cardiac development in HLHS by using patient-derived induced pluripotent stem (iPS) cells. Methods: Five-independent iPS cell lines were generated from HLHS and biventricle (BV) heart-derived cardiac progenitor cells (CPCs). Global gene expression analysis, real-time RT-PCR, mutation analysis, ChIP assay, and cardiac-specific gene promoter activities were examined during differentiation. Results: We found one synonymous single nucleotide polymorphism in NKX2-5 and five in NOTCH1, respectively. Cardiac transcriptional factors such as NKX2-5, HAND1, and NOTCH/HEY, those are known to drive primary heart field and outflow tract development, were significantly reduced in HLHS-derived iPS cells after differentiation compared with BV- and control 201B7 iPS-derived cardiomyocytes. ChIP assay showed that a marked decrease in dimethylated histone H3-lysine 4 and acetylated histone H3 was found within the NKX2-5 promoter regions, whereas a significantly increased trimethylated H3-lysine 27 was identified in differentiated HLHS-derived iPS cells. To specify the target transcripts responsible for cardiac development of HLHS, cardiac troponin-T and natriuretic peptide A promoter analyses were performed. We found that both promoter activities were significantly suppressed in HLHS-derived CPCs and iPS cells compared with those from BV hearts. These repressed promoter activities could be fully restored by transient transfection of NKX2-5, HAND1, and NOTCH1 genes into these stem/progenitor cells by synergistic manner. Conclusions: These findings suggest that patient-specific iPS cells provide a potential to dissecting the complex cardiac malformations in human. The epigenetic and transcriptional regulation of NKX2-5, HAND1, and NOTCH1 may mutually participate in the development of myocardial growth, patterning, and morphogenesis in HLHS.

Early myocardial changes in experimental chick model of hypoplastic left heart syndrome (547.10)

Hypoplastic left heart syndrome (HLHS) is a complex congenital heart defect in which the left ventricle of the heart is critically underdeveloped and unable to effectively supply blood to the body. Early reloading of the hypoplastic left ventricle can induce its growth and maturation and lead to rescue. To analyze the early changes during development of HLHS, we used an experimental chick model of left atrial ligation (LAL). Fertilized eggs were incubated at 37.5 °C. Partial ligation of the left atrium of chick embryonic hearts was performed at the ED4. At ED6, we performed ultrasound biomicroscopy examination of control and ligated hearts, followed by confocal microscopy 3D reconstruction of the left ventricle. Only those LAL hearts with clear phenotype, defined as apex‐forming right ventricle, were included in the quantitative evaluation. The hypoplastic left ventricle was significantly smaller in cross‐section with a total tissue volume less than half that of matched controls. In ovo analysis of circumferential strain from ultrasound showed no difference between the control and LAL group. This data indicate that although there is a clear morphological phenotype at this stage, the myocardial performance is still within normal limits, strengthening the point of early, possibly fetal, intervention for HLHS.Grant Funding Source: Supported by PRVOUK‐P35/LF1/5, RVO: 67985823, GACR P302/11/1308, and Bucknell University PUR grant

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.

Persistent Left Superior Vena Cava: Does it Have a Role in the Pathogenesis of Hypoplastic Left Heart Syndrome?

The coexistence of a persistent left superior vena cava (PLSVC) and congenital anomalies, both cardiac and noncardiac, is well documented, but whether PLSVC contributes to the development of cardiac malformations is controversial. We conducted a retrospective review of perinatal and pediatric autopsies to determine the association between PLSVC and other congenital anomalies. Of 362 patients, 91 (25%) had congenital heart disease and 19 (5.2%) had PLSVC. Eight cases (47%) were associated with specific syndromes, including heterotaxy syndrome, trisomy 18, trisomy 13, and Jacobsen syndrome. Seventeen cases of PLSVC (89%) were associated with congenital heart disease, most of which were complex. Isolated PLSVC was found in 2 cases (11%). Eight of the 19 PLSVC cases (47%) were associated with hypoplastic left heart syndrome (HLHS), a result that was statistically significant (P = 0.041). Left ventricle inflow/outflow obstruction is believed to be a critical pathogenic factor in the development of HLHS. Whereas 5 of 8 cases of HLHS had additional obstructive cardiac outflow tract lesions, 3 of 8 cases did not. PLSVC is known to be able to compromise left ventricle inflow via a dilated coronary sinus, and we speculate that PLSVC may have played a contributing role in the pathogenesis of HLHS in these three cases. As an isolated lesion, PLSVC would not be sufficient to cause HLHS, but it might contribute in combination with other obstructive lesions, or in the setting of other genetic and/or environmental factors still to be defined for HLHS. A larger series will be needed to confirm this hypothesis.