Critical Care Medicine

CHD-single ventricle lesions

Functionally Univentricular Heart or Single Ventricle

Synonyms

Hypoplastic Left Heart Syndrome

Related Conditions

Single Ventricle Lesions

1. Description of the problem

What every clinician needs to know

Functionally univentricular hearts may result from a variety of anatomic lesions. Regardless of the etiology, newborns with these lesions have mixing of the systemic and pulmonary venous return.

Clinical features

May present with symptoms ranging from cyanosis to shock based on the underlying anatomy and relative distribution of pulmonary and systemic blood flow. Patients often present with mild tachypnea, mild cyanosis and a newly diagnosed murmur. Feeding intolerance may be present.

Key management points

Management of an unpalliated univentricular heart focuses on maintaining adequate, but not excessive pulmonary blood flow, while providing adequate systemic blood flow to meet the body’s metabolic demands. Prompt IV access should be obtained and prostaglandin therapy initiated to maintain PDA (patent ductus arteriosus) patency.

The care paradigm has shifted from monitoring for pulmonary overcirculation to monitoring systemic Qs and oxygen delivery. It is understood that the single ventricle is pumping Qp plus Qs and that the distribution of the total output from the single ventricle will determine whether there is adequate Qs and oxygen delivery, given that most neonates with univentricular physiology have a Qp:Qs that is greater than 1:1.

2. Emergency Management

  1. Obtain adequate IV access.

  2. Initiate PGE (prostaglandin) therapy to maintain PDA patency.

  3. If significant respiratory distress or cardiogenic shock is evident, secure the airway (intubate).

  4. Correct metabolic acidosis.

  5. Provide inotropic support (dopamine, epinephrine, calcium chloride).

  6. Echocardiogram to confirm anatomy/physiology.

3. Diagnosis

Diagnostic criteria and tests

The single most important diagnostic test to confirm the diagnosis is an echocardiogram. This will allow for delineation of the anatomy, which may have an impact on the physiologic state of the patient. The key elements include the status of the atrial septum, ventricular function, pulmonary venous return, atrioventricular valve function and PDA patency.

Establishing a diagnosis

Patients with single ventricle physiology can present in multiple ways, depending on the status of the patent ductus arteriosus (PDA) and whether it is critical for pulmonary or systemic blood flow. If the PDA is patent the patient usually presents with cyanosis, normal to mildly elevated respiratory rate and normal heart rate. A PDA murmur may or may not be appreciated. There may or may not be feeding intolerance.

As the PDA closes, in the setting of PDA dependent pulmonary blood flow, the patient will become progressively cyanotic, usually without significant tachypnea. As the PDA closes, in the setting of PDA dependent systemic blood flow, the patient will become progressively acidotic, poorly perfused and lethargic.

Other possible diagnoses

Disease states that most commonly present in a similar fashion include:

  1. Sepsis.

  2. Cardiomyopathy.

  3. Metabolic diseases (inborn errors of metabolism).

Confirmatory tests

The most important test to perform is an echocardiogram. An electrocardiogram and chest X-ray can be performed for ancillary information but are not critical.

4. Specific Treatment

First-line and other therapies

The most critical therapy is initiation of a prostaglandin (PGE) infusion. There is no substitute for a PDA so unless it can be opened or maintained by PGE (extremely rare as a newborn), emergent surgery is needed. After PDA patency is established, additional therapies might include intubation/mechanical ventilation, inotrope therapy (dopamine, epinephrine) or subambient oxygen therapy.

Drugs and dosages

  1. Prostaglandin (PGE) - 0.01-0.05 mcg/kg/min.

  2. Dopamine: 5-20 mcg/kg/min.

  3. Epinephrine: 0.02-0.1 mcg/kg/min.

  4. Milrinone: 0.25-1 mcg/kg/min.

  5. Nipride: 0.5-3 mcg/kg/min.

5. Disease monitoring, follow-up and disposition

With appropriate therapy the patient should have good perfusion, brisk capillary refill, resolution of lactic acidosis and good urine output (at least 1 mL/kg/hr).

The echocardiogram will confirm the diagnosis. The management of the patient's physiology is what is at issue. If the patient does not have good urine output and resolution of lactic acidosis, the balance between systemic and pulmonary is not appropriate and adjustments need to be made.

Most often pulmonary vascular resistance (PVR) needs to be increased (raising the pCO2 and lowering the FiO2), systemic vascular resistance (SVR) needs to be decreased (nipride or milrinone) and total cardiac output needs to be increased (dopamine, epinephrine).

The patient needs to be transferred to a center where pediatric cardiac surgery is performed.

Pathophysiology

As discussed previously, patency of the PDA is obligatory. The systemic and pulmonary venous blood mixes in the atrium, creating a mixture of desaturated and saturated blood. Resistance in the pulmonary circuit is usually lower than that of the systemic circuit and there will be pulmonary over-circulation, limiting the degree of cyanosis.

If the pulmonary over-circulation is significant, congestive heart failure, systemic hypoperfusion and acidosis may occur. Management of an unpalliated univentricular heart focuses on maintaining adequate, but not excessive pulmonary blood flow, while providing adequate systemic blood flow to meet the body’s metabolic demands.

Traditionally, adequacy of support was assessed using oxygen saturation as an indirect measure of Qp:Qs; however, unrecognized pulmonary venous desaturation may confuse the matter. The care paradigm has shifted from monitoring for pulmonary overcirculation to monitoring systemic Qs and oxygen delivery.

It is understood that the single ventricle is pumping Qp plus Qs and that the distribution of the total output from the single ventricle will determine whether there is adequate Qs and oxygen delivery, given that most neonates with univentricular physiology have a Qp:Qs that is greater than 1:1. Non-cardiovascular manipulations to optimize DO2 and minimize VO2 are often employed, including sedation, neuromuscular blockade (if absolutely necessary), and maintenance of normothermia or mild hypothermia.

Epidemiology

Single ventricle, a rare congenital cardiac defect, often occurs as part of a complex phenotype of cardiovascular malformations. Nearly 10% of congenital heart defects belong to the group of functionally univentricular hearts. The natural history of the vast majority is characterized by a fatal course in the neonatal period or in early infancy.

Patients with functionally univentricular hearts represent a heterogeneous group of cardiac malformations almost always determined by a dominant ventricle of either left or right ventricular morphology. The anatomic definition of single ventricle has been a controversial issue for pediatric cardiologists over the years. Single ventricle lesions occurred in 1.25% of infants with congenital cardiovascular defects in the Baltimore-Washington Infant Study.

There are many types of anatomy that result in a univentricular (single ventricle) heart. Perhaps the most commonly thought of lesion (and one of the most challenging) is hypoplastic left heart syndrome (HLHS). This is a type of serious problem that involves several parts of the left side of the heart. It is quite rare and occurs in about 1 out of every five thousand babies born.

In the United States, about 1,000 babies with HLHS are born each year. Two thirds of the babies affected are boys. Most babies with HLHS are otherwise healthy but some have other medical problems including other heart problems, neurologic problems and Turner's syndrome.

Prognosis

Most patients with single ventricle lesions, without treatment, will die within the first month of life. Treatment consists either of three heart surgeries (Norwood, Bidirectional Glenn and Fontan) during the first 2 years of life, or a heart transplant.

Early outcomes for patients with single ventricle lesions have improved substantially over the past three decades. Reports of early postoperative mortality are predominantly from centers achieving excellent outcomes with reported surgical survival of 81% to 93%. Results from multiple centers have been limited to database extraction with a lower survival at 72% to 85%.

Reported risk factors for early mortality after the Norwood procedure differ among centers and include patient-related factors such as prematurity, lower birth weight, presence of genetic or non-cardiac abnormalities; anatomic factors such as mitral stenosis-aortic atresia, smaller ascending aorta, restrictive atrial septum or significant tricuspid regurgitation; preoperative factors such as shock and ECMO; operative factors such as older age at surgery, shunt type, longer DHCA, cardiopulmonary bypass or total support time; and postoperative factors such as ECMO and low mixed venous saturation.

While there is additional mortality risk following the bidirectional Glenn and Fontan operations, it is considerable less (under 5%) unless high risk factors are present. Close follow-up after the Norwood procedure and before the bidirectional Glenn operation (inter-stage period) is warranted, as there is significant risk of mortality (up to 15%).

Special considerations for nursing and allied health professionals.

N/A

What's the evidence?

Tabbutt, S, Ramamoorthy, C, Montenegro, LM. "Impact of inspired gas mixtures on preoperative infants with hypoplastic left heart syndrome during controlled ventilation". Circulation. vol. 104. 2001. pp. I159-64.

(This article reviews the impact of inspired gas mixtures (N2 and CO2) on the balance between pulmonary and systemic blood flow and cardiac ouput in the preoperative patient with single ventricle physiology. It demonstrates the benefit of CO2 over N2 in the ventilated patient.)

Ghanayem, NS, Hoffman, GM, Mussatto, KA. "Perioperative monitoring in high-risk infants after stage 1 palliation of univentricular congenital heart disease". J Thorac Cardiovasc Surg. vol. 140. 2010. pp. 857-63.

(This article reviews the utilization of ICU monitoring tools such as mixed venous saturation and NIRS (near infrared spectroscopy) to guide hemodynamic therapy in patients with single ventricle physiology.)

Tweddell, JS, Ghanayem, NS, Mussatto, KA, Mitchell, ME, Lamers, LJ. "Mixed venous oxygen saturation monitoring after stage 1 palliation for hypoplastic left heart syndrome". Ann Thorac Surg. vol. 84. 2007. pp. 1301-11.

(This article reviews the utilization of mixed venous saturation to guide hemodynamic therapy in post-operative patients with single ventricle physiology and its utility in predicting outcome.)

Kaulitz, R, Hofbeck, M. "Current treatment and prognosis in children with functionally univentricular hearts". Arch Dis Child. vol. 90. 2005. pp. 757-62.

(This article provides a global overview of therapies available in the treatment of patients with single ventricle physiology.)

Ohye, RG, Sleeper, LA, Mahony, L, Newburger, JW, Pearson, GD. "Comparison of shunt types in the Norwood procedure for single-ventricle lesions". N Engl J Med. vol. 362. 2010. pp. 1980-92.

(This article contains the results of the only multicenter randomized trial comparing two different sources of pulmonary blood flow in the Norwood operation.)
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