Hypoplastic Left Heart Syndrome

Sonographic Diagnosis and Differential

Comprehensive approach to prenatal echocardiographic diagnosis

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Definition

Spectrum of cardiac anomalies characterized by underdevelopment of left-sided cardiac structures

  • Hypoplastic or atretic mitral valve
  • Hypoplastic or atretic aortic valve
  • Hypoplastic left ventricle
  • Hypoplastic ascending aorta and aortic arch
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HLHS Anatomy

HLHS Anatomical Diagram
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Epidemiology

Prevalence

2–3 per 10,000 live births

8–9% of all congenital heart disease

Associations

Male predominance (55–67%)

Chromosomal anomalies: 10–30%

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Anatomic Variants

Mitral Stenosis / Aortic Atresia

Most common variant (40%)

Mitral Atresia / Aortic Atresia

Second most common (30%)

Mitral Stenosis / Aortic Stenosis

Variable severity (30%)

All variants result in single-ventricle physiology requiring staged surgical palliation

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Sonographic Approach

Systematic Evaluation

  • Four-chamber view (primary screening view)
  • Left ventricular outflow tract (LVOT)
  • Aortic arch (sagittal and ductal arch views)
  • Color Doppler interrogation
  • Pulsed-wave Doppler of aortic flow
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Four-Chamber View: Key Findings

Primary sonographic hallmark: Disproportionate ventricular chambers

  • Small, slit-like left ventricle
  • Enlarged, dilated right ventricle
  • Apex formed entirely by RV
  • Intact or restrictive atrial septum (prognostic factor)
  • Small or absent mitral valve orifice
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Quantitative Assessment

Measurement Finding in HLHS
LV length < 2 standard deviations below mean
LV/RV length ratio < 0.6
Mitral valve diameter < 5 mm at term
Aortic valve diameter < 3.5 mm at term

Measurements assist diagnosis but visual impression of disproportion is primary

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Four-Chamber View: HLHS

HLHS Four-Chamber View

Note: Small slit-like LV, enlarged RV forming apex, size disproportion between chambers

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LVOT and Aortic Arch

LVOT View

  • Absent or severely diminished aortic outflow
  • Hypoplastic ascending aorta (< 2 mm)
  • No visible aortic valve opening

Aortic Arch

  • Hypoplastic transverse arch
  • Diameter disparity: PA >> Ao
  • Retrograde flow in arch (Doppler)
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Color Doppler: Pathognomonic Findings

Retrograde flow in ascending aorta and transverse arch

  • Coronary and cerebral perfusion via retrograde arch flow from PDA
  • Reversed flow in distal aortic arch (toward heart)
  • Antegrade flow only in descending aorta from ductus
  • Absent or minimal antegrade LVOT flow

Ductal-dependent systemic circulation: PGE₁ required at birth

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Atrial Septum Evaluation

Critical prognostic factor: Degree of interatrial communication

Adequate ASD

Unrestricted left-to-right flow

Better postnatal stability

Restrictive/Intact

Limited left atrial decompression

May require urgent septostomy

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Associated Findings

Cardiac

  • Coarctation of aorta (common)
  • Total anomalous pulmonary venous return (3–6%)
  • Right aortic arch (rare)

Extracardiac

  • Chromosomal: Turner syndrome, Trisomy 13, 18
  • CNS, renal, GI anomalies (screen with detailed anatomy)
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Hemodynamic Circulation

HLHS Hemodynamic Diagram

Ductal-dependent systemic circulation: PDA supplies ascending aorta via retrograde flow

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Differential Diagnosis

Diagnosis Distinguishing Features
Critical aortic stenosis LV may be normal or borderline; valve visible on echo
Coarctation of aorta Normal LV size; isolated arch hypoplasia
Mitral atresia with VSD VSD present; double-outlet RV physiology
Unbalanced AVSD Common AV valve; primum ASD
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Borderline Left Ventricle

Challenging diagnostic and prognostic scenario

  • LV size near lower limits of normal
  • Potential for biventricular vs. single-ventricle repair uncertain
  • Serial echocardiograms may show evolving hypoplasia
  • Postnatal assessment critical for surgical planning

Requires pediatric cardiology consultation for risk stratification

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Timing of Diagnosis

First Trimester

Abnormal 4-chamber may be visible ≥13 weeks

Confirmation with fetal echo 16–18 weeks

Second/Third Trimester

Detailed fetal echocardiography standard

Progressive disproportion may develop

Some cases evolve from initially normal or borderline four-chamber views

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Follow-Up Imaging

Indications for Serial Echocardiography

  • Borderline LV dimensions
  • Assessment of atrial septum (restrictive vs. adequate)
  • Monitor for evolving arch obstruction
  • Evaluate for progressive ventricular disproportion

Typical interval: Every 4 weeks once diagnosis established

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Diagnostic Pitfalls

Avoid over-reliance on four-chamber view alone

  • Subtle disproportion may be missed without LVOT/arch views
  • Early gestation: LV size may appear normal
  • Technical factors: Maternal obesity, fetal position
  • Differentiation from critical AS requires careful Doppler

Complete fetal echocardiogram mandatory for any suspected LV asymmetry

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Prenatal Counseling

Key Discussion Points

  • Single-ventricle physiology requiring staged surgical palliation
  • Three-stage reconstruction (Norwood, Glenn, Fontan)
  • Survival: 50–70% to Fontan completion
  • Long-term morbidity: neurodevelopmental, arrhythmia, heart failure

Multidisciplinary team: Pediatric cardiology and cardiac surgery consultation essential

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Delivery Planning

Location

Tertiary center with pediatric cardiac surgery

Immediate PGE₁ availability

Timing

Aim for 39–40 weeks (avoid prematurity)

Earlier if restrictive atrial septum

Mode of delivery: No evidence for routine cesarean; obstetric indications apply

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Immediate Postnatal Management

Ductal-dependent systemic circulation

  • Prostaglandin E₁ infusion initiated immediately
  • Avoid supplemental oxygen (increases PVR, decreases systemic flow)
  • Echocardiography to confirm anatomy and assess atrial septum
  • Urgent balloon atrial septostomy if restrictive/intact septum

Norwood operation typically in first week of life

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Surgical Outcomes

Stage Timing Survival
Norwood (Stage I) First week of life 70–85%
Glenn (Stage II) 4–6 months 90–95% survival post-Glenn
Fontan (Stage III) 2–4 years 85–95% survival post-Fontan

Long-term: Progressive single-ventricle failure, arrhythmias, protein-losing enteropathy

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Long-Term Neurodevelopmental Risk

Increased risk across multiple domains

  • Executive function deficits (30–50%)
  • Motor coordination challenges
  • Learning disabilities more common than general population
  • Multifactorial: Genetic, perioperative, chronic hypoxia

Early intervention and neurodevelopmental follow-up recommended

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Summary: Sonographic Diagnosis

  • Four-chamber view: Small LV, large RV, apex formed by RV
  • LVOT: Absent or minimal antegrade flow
  • Aortic arch: Hypoplastic; retrograde Doppler flow
  • Atrial septum: Critical to assess; restrictive = poor prognosis
  • Serial imaging: For borderline cases or evolving findings
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Summary: Clinical Management

  • Multidisciplinary prenatal counseling with pediatric cardiology/cardiac surgery
  • Delivery at tertiary center with immediate PGE₁ capability
  • Postnatal: Ductal-dependent; avoid oxygen; urgent septostomy if indicated
  • Three-stage surgical palliation: Norwood, Glenn, Fontan
  • Long-term: Neurodevelopmental surveillance and single-ventricle complications
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Key Takeaway

HLHS diagnosis requires systematic multiplane evaluation with Color Doppler to demonstrate retrograde aortic arch flow

Atrial septum status is the most important prognostic factor for immediate postnatal stability

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