Hypoplastic Left Heart Syndrome (HLHS)

Hypoplastic left heart syndrome (HLHS) is a congenital heart defect that consists of the underdevelopment, or hypoplasia, of the left side of the heart in various degrees. The most notable feature of HLHS is the reduced size and functionality of the left ventricle (LV). Also, HLHS is associated with stenosis, hypoplasia, or atresia of the vessels or atrioventricular valves on the left side of the heart. A mixture of genetic factors and altered fetal blood flow Flow Blood flows through the heart, arteries, capillaries, and veins in a closed, continuous circuit. Flow is the movement of volume per unit of time. Flow is affected by the pressure gradient and the resistance fluid encounters between 2 points. Vascular resistance is the opposition to flow, which is caused primarily by blood friction against vessel walls. Vascular Resistance, Flow, and Mean Arterial Pressure causes HLHS. Hypoplastic left heart syndrome presents once the ductus arteriosus closes physiologically as tachypnea, cyanosis, heart failure, and cardiogenic shock Shock Shock is a life-threatening condition associated with impaired circulation that results in tissue hypoxia. The different types of shock are based on the underlying cause: distributive (↑ cardiac output (CO), ↓ systemic vascular resistance (SVR)), cardiogenic (↓ CO, ↑ SVR), hypovolemic (↓ CO, ↑ SVR), obstructive (↓ CO), and mixed. Types of Shock. Diagnosis can be made pre- or postnatally via echocardiogram. Once detected, surgical treatment is the 1st-line therapy, done in 3 stages.

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Editorial responsibility: Stanley Oiseth, Lindsay Jones, Evelin Maza

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Overview

Definition

Hypoplastic left heart syndrome (HLHS) is characterized by the underdevelopment of the left side of the heart. The components of HLHS include:

  • Left ventricle (LV) with moderate hypoplasia, non-functional hypoplasia, or complete atresia
  • Mitral valve (MV) with stenosis or atresia
  • Aortic valve (AoV) with stenosis or atresia
  • Ascending aorta (Ao) with hypoplasia
  • Atrial septal defect Atrial Septal Defect Atrial septal defects (ASDs) are benign acyanotic congenital heart defects characterized by an opening in the interatrial septum that causes blood to flow from the left atrium (LA) to the right atrium (RA) (left-to-right shunt). Atrial Septal Defect (ASD) and patent foramen ovale Patent Foramen Ovale A patent foramen ovale (PFO) is an abnormal communication between the atria that persists after birth. The condition results from incomplete closure of the foramen ovale. Small, isolated, and asymptomatic PFOs are a common incidental finding on echocardiography and require no treatment. Patent Foramen Ovale (PFO)
Hypoplastic left heart syndrome

Hypoplastic left heart syndrome (HLHS) featuring the direction of blood flow Flow Blood flows through the heart, arteries, capillaries, and veins in a closed, continuous circuit. Flow is the movement of volume per unit of time. Flow is affected by the pressure gradient and the resistance fluid encounters between 2 points. Vascular resistance is the opposition to flow, which is caused primarily by blood friction against vessel walls. Vascular Resistance, Flow, and Mean Arterial Pressure (arrows) and the oxygenation of blood:
Red represents oxygenated blood, blue shows deoxygenated blood, and purple shows mixed blood.
RA: right atrium
RV: right ventricle
LA: left atrium
LV: left ventricle
SVC: superior vena cava Superior vena cava The venous trunk which returns blood from the head, neck, upper extremities and chest. Mediastinum and Great Vessels
IVC IVC The venous trunk which receives blood from the lower extremities and from the pelvic and abdominal organs. Mediastinum and Great Vessels: inferior vena cava Inferior vena cava The venous trunk which receives blood from the lower extremities and from the pelvic and abdominal organs. Mediastinum and Great Vessels
MPA: main pulmonary artery
Ao: aorta
PDA PDA The ductus arteriosus (DA) allows blood to bypass pulmonary circulation. After birth, the DA remains open for up to 72 hours and then constricts and involutes, becoming the ligamentum arteriosum. Failure of this process to occur results in patent ductus arteriosus (PDA), a condition that causes up to 10% of congenital heart defects. Patent Ductus Arteriosus (PDA): patent ductus arteriosus Patent ductus arteriosus The ductus arteriosus (DA) allows blood to bypass pulmonary circulation. After birth, the DA remains open for up to 72 hours and then constricts and involutes, becoming the ligamentum arteriosum. Failure of this process to occur results in patent ductus arteriosus (PDA), a condition that causes up to 10% of congenital heart defects. Patent Ductus Arteriosus (PDA)
TV: tricuspid valve
MV: mitral valve
PV: pulmonary valve
AoV: aortic valve

Image: “Hypoplastic left heart syndrome” by Centers for Disease Control and Prevention. License: CC0, cropped by Lecturio.

Epidemiology

  • Incidence: 2–3 out of every 10,000 live births 
  • Accounts for 2%–3% of all congenital heart diseases
  • Accounts for 25%–40% of neonatal deaths due to cardiac causes 
  • 1.5:1 male-to-female ratio

Variants

There are 3 types of HLHS based on the morphology of the cardiac valves:

  1. Aortic and mitral atresia (interchangeable with HLHS):
    • The most severe form
    • LV is absent or “slit-like” and has no output.
    • Short ascending Ao
    • Dependent on the persistence of a ductus arteriosus for any chance of survival
  2. Aortic atresia plus mitral stenosis Mitral stenosis Mitral stenosis (MS) is the narrowing of the mitral valve (MV) orifice, leading to obstructed blood flow from the left atrium (LA) to the left ventricle (LV). Mitral stenosis is most commonly due to rheumatic heart disease. Mitral stenosis leads to impaired LV diastolic filling, increased LA pressure, and LA dilation. Mitral Stenosis:
    • Hypoplastic ascending Ao
    • LV remodeling and hypertrophy related to the degree of stenosis
    • Minimal LV output
  3. Aortic and mitral stenosis Mitral stenosis Mitral stenosis (MS) is the narrowing of the mitral valve (MV) orifice, leading to obstructed blood flow from the left atrium (LA) to the left ventricle (LV). Mitral stenosis is most commonly due to rheumatic heart disease. Mitral stenosis leads to impaired LV diastolic filling, increased LA pressure, and LA dilation. Mitral Stenosis:
    • The mildest form
    • Stenosed valves lead to LV hypertrophy and eventual cardiac output failure.

Etiology

  • There is a component of genetic predisposition as noted in the 2.5%–5% recurrence rate in siblings: associated with poorer morbidity (severe neurodevelopmental delay) and higher mortality.
  • Associated with chromosomal anomalies, such as:
    • Turner syndrome Turner syndrome Turner syndrome is a genetic condition affecting women, in which 1 X chromosome is partly or completely missing. The classic result is the karyotype 45,XO with a female phenotype. Turner syndrome is associated with decreased sex hormone levels and is the most common cause of primary amenorrhea. Turner Syndrome
    • Trisomy 13 Trisomy 13 Trisomy 13, or Patau syndrome, is a genetic syndrome caused by the presence of 3 copies of chromosome 13. As the 3rd most common trisomy, Patau syndrome has an incidence of 1 in 10,000 live births. Most cases of Patau syndrome are diagnosed prenatally by maternal screening and ultrasound. More than half of the pregnancies result in spontaneous abortions. Patau Syndrome (Trisomy 13)
    • Trisomy 18 Trisomy 18 Edwards syndrome, or trisomy 18, is a genetic syndrome caused by the presence of an extra chromosome 18. The extra chromosome is either from 3 full copies of chromosome 18 or an additional segment of chromosome 18. As the 2nd most common trisomy, Edwards syndrome is seen in 1 out of every 5,500 live births. Edwards Syndrome (Trisomy 18)
    • DiGeorge syndrome DiGeorge syndrome DiGeorge syndrome (DGS) is a condition caused by a microdeletion at location q11.2 of chromosome 22 (thus also called 22q11.2 syndrome). There is a defective development of the third and fourth pharyngeal pouches, leading to thymic and parathyroid hypoplasia (causing T-cell immunodeficiency and hypocalcemia, respectively). DiGeorge Syndrome
  • Postulated to be secondary to reduced blood flow Flow Blood flows through the heart, arteries, capillaries, and veins in a closed, continuous circuit. Flow is the movement of volume per unit of time. Flow is affected by the pressure gradient and the resistance fluid encounters between 2 points. Vascular resistance is the opposition to flow, which is caused primarily by blood friction against vessel walls. Vascular Resistance, Flow, and Mean Arterial Pressure in utero through stenosed or atretic AoVs, which leads to the underdevelopment of the LV and ascending Ao
  • May also be linked to intrauterine infarction and/or infection

Pathophysiology

Normal cardiac physiology Cardiac Physiology A complex system of coordinated electrical circuitry within the heart governs cardiac muscle activity. The heart generates its own electrical impulses within its pacemaker cells. The signal then travels through specialized myocytes, which act as electrical wiring, distributing the signal throughout the heart. Cardiac Physiology and development

  • Systemic circulation Systemic circulation Circulation is the movement of blood throughout the body through one continuous circuit of blood vessels. Different organs have unique functions and, therefore, have different requirements, circulatory patterns, and regulatory mechanisms. Systemic and Special Circulations is maintained in utero via the ductus arteriosus and foramen ovale:
    • Fetal body → vena cavae → right atrium (RA) →  foramen ovale → left atrium (LA) → LV → Ao
    • Also, RA → right ventricle (RV) → ductus arteriosus → Ao 
  • At birth, physiologic changes occur:
    • Ductus arteriosus closes → cessation of blood flow Flow Blood flows through the heart, arteries, capillaries, and veins in a closed, continuous circuit. Flow is the movement of volume per unit of time. Flow is affected by the pressure gradient and the resistance fluid encounters between 2 points. Vascular resistance is the opposition to flow, which is caused primarily by blood friction against vessel walls. Vascular Resistance, Flow, and Mean Arterial Pressure from the RV to the Ao → systemic perfusion is reduced
    • Pulmonary arterial pressure decreases → blood begins to flow Flow Blood flows through the heart, arteries, capillaries, and veins in a closed, continuous circuit. Flow is the movement of volume per unit of time. Flow is affected by the pressure gradient and the resistance fluid encounters between 2 points. Vascular resistance is the opposition to flow, which is caused primarily by blood friction against vessel walls. Vascular Resistance, Flow, and Mean Arterial Pressure from the RV to the pulmonary circulation

In HLHS

  • Survival depends on the patency of the ductus arteriosus and foramen ovale or the presence of an ASD to maintain the following circuit:
    • Pulmonary circulation → LA  → ASD/PFO → RA (mixing of oxygenated and deoxygenated blood) → RV → PDA PDA The ductus arteriosus (DA) allows blood to bypass pulmonary circulation. After birth, the DA remains open for up to 72 hours and then constricts and involutes, becoming the ligamentum arteriosum. Failure of this process to occur results in patent ductus arteriosus (PDA), a condition that causes up to 10% of congenital heart defects. Patent Ductus Arteriosus (PDA) → systemic circulation
    • The blood that is flowing through the Ao has a mix of deoxygenated and oxygenated blood, resulting in hypoxemia.
  • An absence of PDA PDA The ductus arteriosus (DA) allows blood to bypass pulmonary circulation. After birth, the DA remains open for up to 72 hours and then constricts and involutes, becoming the ligamentum arteriosum. Failure of this process to occur results in patent ductus arteriosus (PDA), a condition that causes up to 10% of congenital heart defects. Patent Ductus Arteriosus (PDA), PFO, or ASD results in severe cyanosis, acidosis, cardiogenic failure, and shock Shock Shock is a life-threatening condition associated with impaired circulation that results in tissue hypoxia. The different types of shock are based on the underlying cause: distributive (↑ cardiac output (CO), ↓ systemic vascular resistance (SVR)), cardiogenic (↓ CO, ↑ SVR), hypovolemic (↓ CO, ↑ SVR), obstructive (↓ CO), and mixed. Types of Shock after delivery. 
  • Progressive, severe hypoxemia and reduced systemic perfusion results in heart failure and end-organ damage.
Hlhs vs. Normal heart

The components of HLHS vs. a normal heart

Image: “Hypoplastic left heart syndrome” by Mariana Ruiz. License: Public Domain

Clinical Presentation

  • Infants may be symptomatic or asymptomatic at birth depending on the presence and size of an ASD and PDA PDA The ductus arteriosus (DA) allows blood to bypass pulmonary circulation. After birth, the DA remains open for up to 72 hours and then constricts and involutes, becoming the ligamentum arteriosum. Failure of this process to occur results in patent ductus arteriosus (PDA), a condition that causes up to 10% of congenital heart defects. Patent Ductus Arteriosus (PDA). Small or intact atrial septa are associated with severe and rapidly progressive symptoms.
  • At birth: pale or gray-tinted skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Structure and Function of the Skin (“dusky appearance”)
  • 24–48 hours after birth:
    • The physiologic closure of the ductus arteriosus results in the development or aggravation of symptoms.
    • Poor feeding
    • Lethargy
    • Signs of respiratory distress ( dyspnea Dyspnea Dyspnea is the subjective sensation of breathing discomfort. Dyspnea is a normal manifestation of heavy physical or psychological exertion, but also may be caused by underlying conditions (both pulmonary and extrapulmonary). Dyspnea, tachypnea, nasal flaring)
    • Signs of cardiogenic shock Shock Shock is a life-threatening condition associated with impaired circulation that results in tissue hypoxia. The different types of shock are based on the underlying cause: distributive (↑ cardiac output (CO), ↓ systemic vascular resistance (SVR)), cardiogenic (↓ CO, ↑ SVR), hypovolemic (↓ CO, ↑ SVR), obstructive (↓ CO), and mixed. Types of Shock ( hypotension Hypotension Hypotension is defined as low blood pressure, specifically < 90/60 mm Hg, and is most commonly a physiologic response. Hypotension may be mild, serious, or life threatening, depending on the cause. Hypotension, weak peripheral pulses, cyanosis, cool extremities, metabolic acidosis Metabolic acidosis The renal system is responsible for eliminating the daily load of non-volatile acids, which is approximately 70 millimoles per day. Metabolic acidosis occurs when there is an increase in the levels of new non-volatile acids (e.g., lactic acid), renal loss of HCO3-, or ingestion of toxic alcohols. Metabolic Acidosis, oliguria, or anuria)
  • Physical exam:
    • Single S2 (only the pulmonary valve (PV) can be heard closing)
    • Hyperactive precordium
    • No murmurs are heard.
    • Hepatomegaly 
    • Dysmorphic features of associated chromosomal anomalies

Diagnosis

  • Most cases are detected during a prenatal anatomic scan.
  • Confirmed by an echocardiogram showing:
    • Hypoplastic left heart (hypoplasia of LV, stenotic/atretic mitral and/or AoVs)
    • RV remodeling
    • Increased pulmonary arterial pressure
  • Supportive tests include:
    • Pulse oximetry < 95% 
    • Electrocardiogram Electrocardiogram An electrocardiogram (ECG) is a graphic representation of the electrical activity of the heart plotted against time. Adhesive electrodes are affixed to the skin surface allowing measurement of cardiac impulses from many angles. The ECG provides 3-dimensional information about the conduction system of the heart, the myocardium, and other cardiac structures. Normal Electrocardiogram (ECG) ( ECG ECG An electrocardiogram (ECG) is a graphic representation of the electrical activity of the heart plotted against time. Adhesive electrodes are affixed to the skin surface allowing measurement of cardiac impulses from many angles. The ECG provides 3-dimensional information about the conduction system of the heart, the myocardium, and other cardiac structures. Normal Electrocardiogram (ECG)): non-specific
      • Hard to distinguish P waves
      • Signs of RV hypertrophy
    • Chest X-ray: non-specific
      • Cardiomegaly
      • Prominent pulmonary vasculature
  • For patients in cardiogenic shock Shock Shock is a life-threatening condition associated with impaired circulation that results in tissue hypoxia. The different types of shock are based on the underlying cause: distributive (↑ cardiac output (CO), ↓ systemic vascular resistance (SVR)), cardiogenic (↓ CO, ↑ SVR), hypovolemic (↓ CO, ↑ SVR), obstructive (↓ CO), and mixed. Types of Shock, blood work and arterial blood gas (ABG) are needed to assess acidosis secondary to lactic acid buildup.
Hypoplastic left heart syndrome - fetal echocardiography

Postnatal transthoracic echocardiography (4-chamber view):
Severe hypoplasia of the LV with hypoplasia of the LA are seen.
LA: left atrium
LV: left ventricle
RA: right atrium
RV: right ventricle

Image: “Hypoplastic left heart syndrome” by Director of Pediatric Echocardiography, Department of Congenital Heart Disease, Evelina Children’s Hospital, Guy’s and St Thomas’ NHS Foundation Trust, London, UK. License: CC BY 2.0

Management

Emergent management of shock Shock Shock is a life-threatening condition associated with impaired circulation that results in tissue hypoxia. The different types of shock are based on the underlying cause: distributive (↑ cardiac output (CO), ↓ systemic vascular resistance (SVR)), cardiogenic (↓ CO, ↑ SVR), hypovolemic (↓ CO, ↑ SVR), obstructive (↓ CO), and mixed. Types of Shock

  • Prostaglandin E1 infusion to keep the ductus arteriosus patent
  • Inotropes for hypotension Hypotension Hypotension is defined as low blood pressure, specifically < 90/60 mm Hg, and is most commonly a physiologic response. Hypotension may be mild, serious, or life threatening, depending on the cause. Hypotension
  • Bicarbonate infusion for metabolic acidosis Metabolic acidosis The renal system is responsible for eliminating the daily load of non-volatile acids, which is approximately 70 millimoles per day. Metabolic acidosis occurs when there is an increase in the levels of new non-volatile acids (e.g., lactic acid), renal loss of HCO3-, or ingestion of toxic alcohols. Metabolic Acidosis
  • Balloon septoplasty to enlarge a small or deficient foramen ovale

Surgical management

  • 3-staged procedure includes the Blalock-Taussig Shunt, Glenn, and Fontan procedures
  • The goal is to create a larger outflow for the LV and pulmonary circulation that bypasses the RV so that it may be used exclusively for systemic circulation.

Prognosis

  • Left untreated, HLHS is fatal within the 1st few weeks of life.
  • Good tolerance to exercise after surgery
  • Children who complete all 3 stages of surgery have a survival rate of 90% into adulthood.

Clinical Relevance

The following genetic syndromes are associated with the development of HLHS:

  • Turner syndrome Turner syndrome Turner syndrome is a genetic condition affecting women, in which 1 X chromosome is partly or completely missing. The classic result is the karyotype 45,XO with a female phenotype. Turner syndrome is associated with decreased sex hormone levels and is the most common cause of primary amenorrhea. Turner Syndrome: a chromosomal aberration that produces a 45-chromosome karyotype with an X0 female phenotype. Presents with decreased sex hormone levels; primary amenorrhea Primary Amenorrhea Primary amenorrhea is defined as the absence of menstruation in a girl by age 13 years in the absence of secondary sex characteristics or by the age of 15 years with the presence of secondary sex characteristics. Etiologies can originate in the hypothalamic-pituitary-ovarian (HPO) axis or from anatomic abnormalities in the uterus or vagina. Primary Amenorrhea; cardiac, renal, reproductive, skeletal, and lymphatic anomalies; short stature; webbed neck; broad chest; low posterior hairline; and peripheral edema Edema Edema is a condition in which excess serous fluid accumulates in the body cavity or interstitial space of connective tissues. Edema is a symptom observed in several medical conditions. It can be categorized into 2 types, namely, peripheral (in the extremities) and internal (in an organ or body cavity). Edema of the hands and feet. 
  • Holt-Oram syndrome: an autosomal dominant Autosomal dominant Autosomal inheritance, both dominant and recessive, refers to the transmission of genes from the 22 autosomal chromosomes. Autosomal dominant diseases are expressed when only 1 copy of the dominant allele is inherited. Autosomal Recessive and Autosomal Dominant Inheritance condition characterized by the concurrence of congenital cardiopathy, and hypoplastic or aplastic radii and thumbs. 
  • Jacobsen syndrome: a genetic syndrome characterized by the deletion of the long arm Arm The arm, or "upper arm" in common usage, is the region of the upper limb that extends from the shoulder to the elbow joint and connects inferiorly to the forearm through the cubital fossa. It is divided into 2 fascial compartments (anterior and posterior). Arm of the 11th chromosome. Ventricular septal defect and left heart obstructive malformations, including HLHS, are the most commonly associated cardiopathies in Jacobsen syndrome.

The following conditions are differential diagnoses of HLHS:

  • Atrioventricular septal defect: a rare congenital heart defect characterized by the abnormal development of the atrial and ventricular septa and valves. Infants usually present with cyanosis, dyspnea Dyspnea Dyspnea is the subjective sensation of breathing discomfort. Dyspnea is a normal manifestation of heavy physical or psychological exertion, but also may be caused by underlying conditions (both pulmonary and extrapulmonary). Dyspnea, pulmonary edema Pulmonary edema Pulmonary edema is a condition caused by excess fluid within the lung parenchyma and alveoli as a consequence of a disease process. Based on etiology, pulmonary edema is classified as cardiogenic or noncardiogenic. Patients may present with progressive dyspnea, orthopnea, cough, or respiratory failure. Pulmonary Edema, tachypnea, tachycardia, and eventually develop congestive heart failure Congestive heart failure Congestive heart failure refers to the inability of the heart to supply the body with normal cardiac output to meet metabolic needs. Echocardiography can confirm the diagnosis and give information about the ejection fraction. Congestive Heart Failure.
  • ASD: a common congenital heart defect characterized by the presence of an opening between the 2 atria of the heart. Patients present with dyspnea Dyspnea Dyspnea is the subjective sensation of breathing discomfort. Dyspnea is a normal manifestation of heavy physical or psychological exertion, but also may be caused by underlying conditions (both pulmonary and extrapulmonary). Dyspnea, increased susceptibility to respiratory infections, cyanosis, and embolism, but the appearance and severity of symptoms will depend on the size of the defect.
  • Ventricular septal defect (VSD): a common congenital heart defect characterized by abnormal communication between the LV and RV that results in the left-to-right shunting of blood flow Flow Blood flows through the heart, arteries, capillaries, and veins in a closed, continuous circuit. Flow is the movement of volume per unit of time. Flow is affected by the pressure gradient and the resistance fluid encounters between 2 points. Vascular resistance is the opposition to flow, which is caused primarily by blood friction against vessel walls. Vascular Resistance, Flow, and Mean Arterial Pressure. Presents as an holosystolic murmur, with progressive signs of heart failure and cardiogenic shock Shock Shock is a life-threatening condition associated with impaired circulation that results in tissue hypoxia. The different types of shock are based on the underlying cause: distributive (↑ cardiac output (CO), ↓ systemic vascular resistance (SVR)), cardiogenic (↓ CO, ↑ SVR), hypovolemic (↓ CO, ↑ SVR), obstructive (↓ CO), and mixed. Types of Shock
  • MV stenosis: a rare heart defect characterized by the reduced size of the valve communicating the LA and LV. Symptoms vary greatly depending on the size of the valve and whether the malformation is congenital or acquired. Presents as coughing, dyspnea Dyspnea Dyspnea is the subjective sensation of breathing discomfort. Dyspnea is a normal manifestation of heavy physical or psychological exertion, but also may be caused by underlying conditions (both pulmonary and extrapulmonary). Dyspnea, palpitations, frequent respiratory infections, weakness, and chest pain Chest Pain Chest pain is one of the most common and challenging complaints that may present in an inpatient and outpatient setting. The differential diagnosis of chest pain is large and includes cardiac, gastrointestinal, pulmonary, musculoskeletal, and psychiatric etiologies. Chest Pain.

References

  1. Bardo, D. M. E., Frankel, D. G., Applegate, K. E., Murphy, D. J., & Saneto, R. P. (2001). Hypoplastic left heart syndrome. RadioGraphics, 21(3), 705-717. DOI:10.1148/radiographics.21.3.g01ma09705
  2. Kliegman, R. M., M.D., St Geme, Joseph W., MD, Blum, N. J., M.D., Shah, Samir S., M.D., M.S.C.E., Tasker, Robert C., M.B.B.S., M.D., & Wilson, Karen M., M.D., M.P.H. (2020). Cyanotic congenital heart disease: Lesions associated with decreased pulmonary blood flow. In R. M. Kliegman MD, J. W. St Geme MD, N. J. Blum MD, Shah, Samir S., MD, MSCE, Tasker, Robert C., MBBS, MD & Wilson, Karen M., MD, MPH (Eds.), Nelson textbook of pediatrics (pp. 239-2407.e1). https://www.clinicalkey.es/#!/content/3-s2.0-B9780323529501004570
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  4. Lara, D. A., Ethen, M. K., Canfield, M. A., Nembhard, W. N., & Morris, S. A. (2017). A population-based analysis of mortality in patients with Turner syndrome and hypoplastic left heart syndrome using the Texas Birth Defects Registry. Congenital heart disease, 12(1), 105–112.
  5. Glauser, T. A., Zackai, E., Weinberg, P., & Clancy, R. (1989). Holt-Oram syndrome associated with the hypoplastic left heart syndrome. Clinical genetics, 36(1), 69–72. DOI:10.1111/j.1399-0004.1989.tb03369.x
  6. Mattina, T., Perrotta, C. S., & Grossfeld, P. (2009). Jacobsen syndrome. Orphanet journal of rare diseases, 4, 9. DOI:10.1186/1750-1172-4-9
  7. Mäkikallio, K., McElhinney, D. B., Levine, J. C., Marx, G. R., Colan, S. D., Marshall, A. C., Lock, J. E., Marcus, E. N., & Tworetzky, W. (2006). Fetal aortic valve stenosis and the evolution of hypoplastic left heart syndrome: patient selection for fetal intervention. Circulation, 113(11), 1401–1405. https://doi.org/10.1161/CIRCULATIONAHA.105.588194

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