eMedicine Specialties > Pediatrics: Cardiac Disease and Critical Care Medicine > Cardiology

Single Ventricle

Author: Alvin J Chin, MD, Professor of Pediatrics, Division of Cardiology, The Children's Hospital of Philadelphia, University of Pennsylvania School of Medicine
Contributor Information and Disclosures

Updated: Oct 3, 2007

Introduction

Background

In this article, single ventricle is anatomically defined as a heart that is missing the smooth (ie, nontrabeculated) inflow region of either ventricle. Most cases of tricuspid atresia and mitral atresia retain at least a remnant of this smooth septal aspect of the right ventricle (RV) or left ventricle (LV), respectively. Thus, the atrioventricular connection in single ventricle is either double-inlet (2 or more atrioventricular orifices) or common-inlet (common atrioventricular orifice). With a better understanding of cardiovascular morphogenesis, the morphologic RV and morphologic LV may eventually be defined with molecular markers. Currently, the most reliable antemortem method of identifying single ventricle is with 2-dimensional echocardiography.

Much of the surgical literature over the last 30 years uses a functional definition; namely, that single ventricle is present when 1 of the 2 ventricles is small enough that a series circuit (systemic venous return to ventricle 1 to pulmonary arteries to pulmonary venous return to ventricle 2 to systemic arteries) is incompatible with survival.

Until the early 1970s, surgical management did not include separating the pulmonary and systemic circulations. Modifications of the procedure initially proposed in 1971 by Fontan for tricuspid atresia have been widely adopted in the last 2 decades.1 These cavopulmonary or atriopulmonary modifications effectively channel the systemic venous blood directly into the pulmonary arteries. Whether the effect on overall quality of life is superior to that of the more limited palliations used before 1971 is still unclear. Hepatic dysfunction, protein-losing enteropathy, and, most ominously, disadvantageous ejection efficiency combined with elevated afterload characterize Fontan-type circulation.

Single LV is a relatively uncommon disorder in which the RV is rudimentary and consists of only an arterial outflow. The single LV communicates with the rudimentary RV via a bulboventricular foramen (outlet foramen). The rarely observed single RV occurs when no discernible LV is present. Both atria connect to the single ventricle via either a common atrioventricular valve (sometimes termed the common-inlet ventricle) or separate atrioventricular valves (double-inlet ventricle). Single ventricle most frequently occurs with transposition, but any ventriculoarterial alignment can be seen. Subpulmonary stenosis is more prevalent than the combination of aortic arch obstruction and subaortic stenosis. Although rare, single ventricle can occur without stenosis of either pulmonary or aortic outflow.

The embryology of single ventricle is still unknown. Presumably, both ventricular septation and movement of the common atrioventricular orifice are disrupted. In fact, many genetic alterations can likely result in a single ventricle phenotype. Five single-gene targeted disruptions in mice (Nkx2.5, Isl1, Mef2c, Hand2, and fog-2) have already been reported to result in single ventricle prenatally. The fog -2 null mouse also displays a common atrioventricular orifice situated almost entirely over the future LV.

Pathophysiology

No circulatory derangement is observed in fetal development because pulmonary circulation and systemic circulation are normally in parallel, with 2 levels of connection: atrial and ductal. However, lack of separation between pulmonary and systemic circulations causes obvious cyanosis postnatally, with severity dependent on the degree of coexistent subpulmonary stenosis. Although cases of single ventricle and arch obstruction are the least cyanotic because they never display subpulmonary stenosis, such patients are vulnerable to poor lower body perfusion upon reduction in ductal diameter.

Frequency

United States

Single ventricle occurs in approximately 5 of every 100,000 live births.

Mortality/Morbidity

The severity and timing of presentation depend on the extent of coexistent subpulmonary stenosis (or, alternatively, aortic obstruction) and on reduction in caliber of the ductus arteriosus.

Sex

No disparities are known.

Age

Presentation is generally within the first month of life. As the ductus arteriosus reduces in caliber within the first few days of life, those infants with severe subpulmonary stenosis or aortic obstruction present with cyanosis or poor peripheral perfusion, respectively.

Clinical

History

  • Neonates with single ventricle and subpulmonary stenosis become cyanotic but are usually without other symptoms.
  • Neonates with single ventricle and aortic obstruction may have rapid breathing, lethargy, and poor feeding.

Physical

  • Cyanosis is present in patients with subpulmonary stenosis.
  • Poor peripheral perfusion is evident in patients with single ventricle with aortic obstruction.
  • If aortic obstruction involves coarctation or interruption, then a difference in blood pressure is observed between the right arm and a lower extremity, unless the right subclavian artery is aberrant. 
  • The first heart sound is normal.
  • The second heart sound is single.
  • A systolic ejection murmur is present in those with subpulmonary stenosis as well as those with aortic obstruction.

Causes

  • The cause of single ventricle is unknown.
  • So far, 5 targeted single-gene disruptions in mice have produced a right ventricular (RV) hypoplasia phenotype reminiscent of single left ventricle (LV). These disruptions include global nulls in Nkx2.5, Isl1, Mef2c, dHand (also known as Hand2), and fog-2. The fog -2 null also displays a common atrioventricular orifice situated almost entirely over the future LV. Whether hypomorphic alleles of the homologous mutations in the human produce a single ventricle phenotype but do not result in embryonic lethality remains to be shown.
  • The myocardial-specific inactivation of GATA4 also causes single ventricle.

More on Single Ventricle

Overview: Single Ventricle
Differential Diagnoses & Workup: Single Ventricle
Treatment & Medication: Single Ventricle
Follow-up: Single Ventricle
Multimedia: Single Ventricle
References
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References

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Further Reading

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Keywords

single ventricle, single left ventricle, single right ventricle, tricuspid atresia, mitral atresia, double-inlet single ventricle, common-inlet single ventricle, hepatic dysfunction, protein-losing enteropathy, subpulmonary stenosis, aortic arch obstruction, aortic arch hypoplasia, subaortic stenosis, cyanosis, peripheral perfusion, Fontan operation, hypoproteinemia, L-looped single left ventricle, transposition of the great arteries, D-looped single left ventricle, bulboventricular foramen, outlet foramen, bidirectional Glenn operation, pulmonary artery distortion, pericardial effusion, pleural effusion, ascites, thrombus, sinus bradycardia, atrial flutter

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Contributor Information and Disclosures

Author

Alvin J Chin, MD, Professor of Pediatrics, Division of Cardiology, The Children's Hospital of Philadelphia, University of Pennsylvania School of Medicine
Alvin J Chin, MD is a member of the following medical societies: American Association for the Advancement of Science and American Heart Association
Disclosure: Nothing to disclose.

Medical Editor

Juan Carlos Alejos, MD, Assistant Clinical Professor, Department of Pediatrics, Division of Cardiology, University of California at Los Angeles
Juan Carlos Alejos, MD is a member of the following medical societies: American Academy of Pediatrics, American College of Cardiology, American Heart Association, American Medical Association, and International Society for Heart and Lung Transplantation
Disclosure: Nothing to disclose.

Pharmacy Editor

Mary L Windle, PharmD, Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy, Pharmacy Editor, eMedicine.com, Inc
Disclosure: Nothing to disclose.

Managing Editor

Ameeta Martin, MD, Associate Professor, Department of Pediatrics, Section of Pediatric Cardiology, University of Nebraska College of Medicine
Ameeta Martin, MD is a member of the following medical societies: American College of Cardiology
Disclosure: Nothing to disclose.

CME Editor

Gilbert Herzberg, MD, Assistant Professor, Department of Pediatrics, Section of Pediatric Cardiology, New York Medical College
Gilbert Herzberg, MD is a member of the following medical societies: American Academy of Pediatrics
Disclosure: Nothing to disclose.

Chief Editor

Steven Neish, MD, Director of Pediatric Cardiology Fellowship Program, Department of Pediatrics, Baylor College of Medicine; Clinical Director of Pediatric Cardiology, Texas Children's Heart Center; Director, Brown Foundation Heart Clinic, Texas Children's Hospital
Steven Neish, MD is a member of the following medical societies: American Academy of Pediatrics, American College of Cardiology, and American Heart Association
Disclosure: Nothing to disclose.

 
 
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