Pediatric Hypoplastic Left Heart Syndrome Workup

Updated: Dec 15, 2020
  • Author: Syamasundar Rao Patnana, MD; Chief Editor: Stuart Berger, MD  more...
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Laboratory Studies

Laboratory studies indicated in workup of hypoplastic left heart syndrome (HLHS) are summarized below.

Complete blood cell count

Measure hemoglobin levels, because severe neonatal anemia can cause high-output congestive heart failure (CHF) and cardiogenic shock. The hemoglobin level is usually normal in hypoplastic left heart syndrome.

Obtain a total white blood cell (WBC) count with differential. Sepsis can cause symptoms of shock. The WBC count is typically normal.

Electrolyte levels

Electrolyte abnormalities may be present in infants with poor oral intake secondary to CHF. Use carbon dioxide and bicarbonate to assess acid-base status.

Electrolyte levels are usually normal. The carbon dioxide level may be low if a metabolic acidosis is present. The carbon dioxide level may be high if respiratory failure sets in.

BUN/creatinine levels

Infants with critical illness and significantly reduced systemic perfusion may show evidence of renal failure. The creatinine level may be transiently elevated.

Liver function tests

Infants with critical illness and significantly reduced systemic perfusion and CHF may show evidence of hepatocellular damage.

Aspartate aminotransferase (AST) and alanine aminotransferase (ALT) levels may be transiently elevated.

Arterial blood gas and lactic acid measurements

Assessing acid-base status is paramount, especially to rule out metabolic acidosis. Most infants have some evidence of metabolic acidosis, which should be immediately corrected. This is usually secondary to decreased systemic perfusion. Appropriate intervention to augment systemic flow should be promptly undertaken. Elevated levels of serum lactic acid generally precede a fall in pH, as acidosis develops.

Assessment of PaO2 and PaCO2 is important for respiratory management and manipulation of pulmonary vascular resistance by mechanical ventilation and the addition of supplemental inhaled nitrogen. The PaO2 is optimally 30-45 mm Hg, and the PaCO2 is ideally 45-50 mm Hg.

Karyotype analysis

Chromosomal analysis is indicated for infants with dysmorphic features. Nearly 25% of infants have chromosomal abnormalities.

Other studies


Electrocardiography typically reveals sinus tachycardia, right-axis deviation, right atrial enlargement, and right ventricular hypertrophy with a qR configuration in the right precordial leads.

A paucity of left ventricular forces is noted in the left precordial leads.

ST-T wave changes suggestive of myocardial ischemia may be present in some patients.


Imaging Studies

Chest radiography

Cardiomegaly and increased pulmonary vascular markings are typically present.

Marked pulmonary edema may be noted in infants with obstructed pulmonary venous return, usually due to markedly restrictive patent foramen ovale.

Although the radiography findings are not specific for the condition, the presence of a large heart with increased pulmonary vascular markings in a mildly cyanotic neonate should always prompt inclusion of hypoplastic left heart syndrome in the differential diagnosis.


Echocardiography is the test of choice for diagnosing hypoplastic left heart syndrome. Two-dimensional imaging clearly shows the hypoplastic left ventricle and ascending aorta. The right atrium, tricuspid valve, right ventricle, and main pulmonary artery are larger than usual. See the images below.

This echocardiographic still frame shows a long-ax This echocardiographic still frame shows a long-axis view of the aortic arch in a patient with hypoplastic left heart syndrome (HLHS). The ascending aorta is markedly hypoplastic, serving only to deliver blood in a retrograde fashion to the coronary arteries. An echo-bright coarctation shelf is seen at the insertion of the ductus arteriosus.
This echocardiographic still frame shows a 4-chamb This echocardiographic still frame shows a 4-chamber view of the heart in a patient with hypoplastic left heart syndrome (HLHS). A large right ventricle (RV) and hypoplastic left ventricle (star) are seen. Right atrium = RA. Left atrium = LA.

Other structural abnormalities should be excluded.

Doppler and color Doppler imaging are also important. [4]

Evaluate tricuspid regurgitation, which is a preoperative risk factor for the Norwood procedure, and blood flow across the atrial septum. High-velocity Doppler jet across the atrial septum indicates restrictive interatrial communication. Observe retrograde blood flow from the ductus arteriosus into the transverse aortic arch and ascending aorta.

Evaluate the aortic arch and thoracic aorta for evidence of coarctation.

Two-dimensional and Doppler echocardiographic features are sufficiently characteristic of hypoplastic left heart syndrome such that cardiac catheterization and angiography are no longer necessary for diagnosis of this anomaly.

Variability of the chamber and vessel size is seen in hypoplastic left heart syndrome.

Ultrasonography of the head and abdomen

Ultrasonography of the head was thought to be necessary only if the infant has had a significantly long period in shock with potentially poor cerebral perfusion. However, at most institutions, routine head ultrasonography to exclude central nervous system abnormality and abdominal ultrasonography to evaluate kidneys are performed prior to the Norwood procedure or cardiac transplantation.

A significant prevalence of abnormalities is observed using ultrasonography of the head [32] and abdomen.



Cardiac catheterization (pre–Norwood procedure)

Routine diagnostic catheterization is not necessary because 2-dimensional and Doppler echocardiography can provide the necessary anatomic and hemodynamic data. However, a focused catheterization may become necessary to resolve any echocardiographic discrepancies that may be deemed important in surgical management.

If catheterization is performed, the features reflect the pathophysiology described above.

Oxygen saturation data indicate moderate-to-severe systemic venous desaturation, with a step-up at the level of right atrium secondary to left to right shunt across the atrial septum. The oxygen saturations in the right ventricle, pulmonary artery and aorta are similar reflecting common mixing in the right atrium. Mild systemic arterial desaturation is usually present unless severe pulmonary edema is noted.

The right atrial pressure is mildly elevated, and the left atrial pressure is moderate to severely elevated, unless a large atrial septal defect is present. The right ventricular and pulmonary arterial systolic pressures are at systemic level. If the ductus arteriosus is constricted, these pressures are higher than those in the aorta.

Angiography, although not necessary in all cases, reveals hypoplasia of the mitral valve, left ventricle and aorta. The ascending aorta is perfused in a retrograde fashion and serves as a common coronary artery, supplying both the right and left coronary arteries.

Perform interventional catheterization with blade/balloon atrial septostomy or static dilatation of the atrial septum to relieve pulmonary venous hypertension if blood flow from left atrium to right atrium is severely restricted at the atrial septum. [33, 34] Because of marked hypoplasia of the left atrium, conventional Rashkind balloon or Park blade atrial septostomy may not be possible. In such situations, static dilatation of the atrial septum may be performed. [34, 35] If the atrial septum is extremely thick with a markedly restrictive atrial septum, stent implantation to keep the atrial septum open may become necessary. [34]

When hybrid procedures are contemplated, stenting of the ductus, atrial septum, or both may become necessary.

Cardiac catheterization (pre–bidirectional Glenn [stage II] procedure)

Perform routine catheterization before the operation to obtain hemodynamic data and several important angiograms.

Calculate pulmonary vascular resistance to ensure the patient's suitability for the stage II procedure.

Perform angiography in the right ventricle to show ventricular function and tricuspid regurgitation.

Perform angiography in the transverse aortic arch near the shunt to show pulmonary artery size and distribution and to rule out recurrent aortic coarctation or significant aortopulmonary collateral vessels.

If collateral vessels are found, they may be occluded with coils at the same catheterization.

Pre-Fontan (stage III) procedure

Routine catheterization before completing the operation is generally recommended.

Measure pulmonary artery pressure and calculate pulmonary vascular resistance and perform right ventricular angiography.

Delineate pulmonary artery anatomy by performing angiography at the superior vena cava–pulmonary artery anastomosis via an internal jugular approach.

Recurrent coarctation of the aorta and significant collateral vessels are excluded again.

Descending aortography and selective right and left subclavian artery angiography to identify any collateral vessels to lungs is recommended.

Postcatheterization complications include hemorrhage, vascular disruption after balloon dilation, pain, nausea and vomiting, and arterial or venous obstruction from thrombosis or spasm but are rare.

Catheter intervention

In the neonate, obstruction at the level of the patent foramen ovale (atrial septum) may be treated with conventional Rashkind balloon atrial septostomy. However, because the left atrium is small, Rashkind septostomy [33] may not be feasible. In addition, the septum may be too thick to be torn by balloon septostomy; therefore, Park blade septostomy may be necessary and should precede the Rashkind procedure. [36, 37] However, hypoplastic left atrium may preclude blade septostomy. Static dilatation of the atrial septum with a balloon angioplasty catheter may be used and may not only relieve the obstruction but also keep some restriction, such that no rapid fall in the pulmonary vascular resistance occurs. Static balloon dilatation is preferred by the senior author. [34, 35]

In some patients, the atrial septum may be intact or have a tight patent foramen ovale that may not even allow passage of a catheter. In such situations, puncture of the atrial septum by a Brockenbrough technique or radiofrequency perforation of the atrial septum followed by static balloon atrial septal dilatation or, preferably, stent implantation may become necessary. [34, 38]

If progressive cyanosis develops after a previous Blalock-Taussig shunt, and if the hypoxemia is due to a stenotic shunt, balloon dilatation may be used to improve oxygen saturation. [39] However, if the patient is of sufficient size and age to undergo a bidirectional Glenn procedure, this procedure should be performed instead of balloon angioplasty of a narrowed Blalock-Taussig shunt.

If severe aortic coarctation is present, particularly after Norwood procedure, balloon angioplasty may be useful in relieving aortic obstruction and may help achieve reduce right ventricular afterload. [40]

If significant branch pulmonary artery stenosis is present before a bidirectional Glenn or Fontan conversion or after a Fontan procedure, balloon angioplasty or placement of intravascular stents is recommended. [41, 42]

Development of aortopulmonary collateral vessels has been increasingly observed in recent studies. Before the final Fontan conversion, occlusion of these vessels in the catheterization laboratory, usually by means of coil embolization, [43, 44] is recommended to reduce left ventricular volume overloading and, probably, the duration of chest tube drainage following surgery.

Following completion of Fontan procedure, some patients may develop recurrent pleural effusion, liver dysfunction, plastic bronchitis or protein-losing enteropathy. [45] In these patients, following exclusion of obstructive lesion in the Fontan circuit, puncture of the atrial septum by a Brockenbrough technique followed by static balloon atrial septal dilatation or stent implantation may be beneficial.

Patients who have undergone a fenestrated Fontan operation or have a residual atrial defect, despite correction, may have significant right-to-left shunting causing severe hypoxemia. These residual atrial defects may be closed using transcatheter techniques. [46, 47]