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Single Ventricle - An Overview

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It is a congenital heart abnormality with life-threatening consequences if not treated promptly. Read the article to know more.

Medically reviewed by

Dr. Yash Kathuria

Published At March 24, 2023
Reviewed AtJune 13, 2023

Introduction

It is a rare birth defect in which a child is born with only one ventricle and other associated abnormalities. A normal heart has four chambers, two on the right- a right atrium and a right ventricle, and two on the left- a left atrium and a left ventricle. The heart’s right side pumps deoxygenated blood to the lungs, where it gets oxygenated and returned to the left side of the heart for distribution.

In a heart with a single ventricle, one of the ventricles is underdeveloped, and the other must do all the work at times. Babies with a single ventricle will develop heart rhythm disturbances such as tachycardia (faster-than-normal heartbeat), atrial flutter (abnormal heart rhythm), bradycardia (slower heart rate), heart failure, and liver and kidney failure.

These individuals are at a greater risk for weakening and failing heart muscles and developing thrombus (blood clots). They also do not grow well and have reduced tolerance for exercise. Treatment involves prompt surgery and rehabilitation, and if left untreated, there is a 90% chance of mortality.

What Causes Single Ventricle?

A combination of genetic and environmental factors is thought to cause a single ventricle. It is an associated complication of various genetic conditions like:

  1. Situs Inversus Totalis- A condition in which the organs in the chest and abdomen are positioned in a mirror image of normal human anatomy.

  2. Heterotaxy- It is an abnormality where the internal thoracoabdominal organs demonstrate abnormal arrangement across the left axis of the body.

  3. Primary Ciliary Dyskinesia- It is a disorder characterized by chronic respiratory tract infections, abnormally positioned internal organs, and the inability to have children.

Single ventricle has also been occasionally observed in conditions like:

  1. Inactivation of Tbx5 and GATA4 genes.

  2. Defective formation of endocardial cushions.

  3. Developmental disturbances in dynamic blood flow.

  4. DiGeorge syndrome (a condition caused due to defects in chromosome 22).

Some of the environmental factors that might increase the risk of the single ventricle are:

  1. Advanced parental age.

  2. Phenylketonuria (build-up of an amino acid called phenylalanine).

  3. Pregestational diabetes (pregnancy-induced diabetes).

  4. Febrile illness.

  5. Influenza.

  6. Viral infection (especially rubella).

  7. Medications including lithium.

  8. Marijuana addiction.

What Are the Different Types of Single Ventricle Defects?

The term single ventricle is an umbrella term for various types of single ventricle defects, some of them are:

  1. Hypoplastic Left Heart Syndrome (HLHS)- It is a type of single ventricle defect in which chambers of the left side of the heart are small and underdeveloped, with valves that do not work properly. A newborn with HLHS may seem to be doing well during the first few hours of life; however, the natural openings between the heart’s left and right sides close a day or two after birth. This is normal for a baby, but in babies with HLHS, this can be fatal because it leaves with an overworked right heart which will not be able to pump blood to the entire body.

  2. Tricuspid Atresia- This variation of the single ventricle defect is caused due to an underdeveloped tricuspid valve (connects the right atrium and the right ventricle). An underdeveloped tricuspid valve means the blood cannot reach the lungs to be oxygenated.

  3. Single Left Ventricle- This defect occurs when one ventricle of the heart (typically the right ventricle) is underdeveloped, and both atria (right and left atrium) connect to the working ventricle resulting in the blood that cannot be pumped to the lungs for normal oxygenation.

  4. Mitral Valve Atresia- It is caused due to improper development of mitral valves, which is the connecting valve between the left atrium and the left ventricle.

  5. Double Outlet Right Ventricle- It is a single ventricle defect in which the aorta (which is supposed to be attached to the left ventricle) and the pulmonary artery are connected to the right ventricle leading to the mixing of the oxygenated and deoxygenated blood, respectively.

What Are the Symptoms of Single Ventricle Defect?

Babies born with a single ventricle will be critically ill and will require immediate care. Some of the symptoms of single ventricle defects are-

  1. Cyanosis (bluish tone of the skin, lips, and nails).

  2. Pale, cool, and clammy skin.

  3. Difficulty in breathing.

  4. Accelerated heart rate.

  5. Heart murmur.

How Are Single Ventricle Defects Diagnosed?

Diagnosing a single ventricular defect is a time-sensitive procedure. The healthcare provider (usually a pediatric cardiologist) will immediately request any of the following tests as soon as they suspect cardiac anomalies during the physical exam:

  1. Chest X-Ray- Usually done to determine the baby's heart size and structure.

  2. Cardiac Magnetic Resonance Imaging (MRI)- Helps to determine the blood flow and the functioning of the heart.

  3. Electrocardiogram (ECG or EKG)- Helps to identify abnormal heart rhythms and heart muscle stress.

  4. Echocardiogram (Echo)- It is similar to an ultrasound and helps to identify the structure and position of the parts of the heart and heart defects.

  5. Cardiac Catheterization- Helps to measure blood pressure and oxygen levels.

How Is a Single Ventricle Treated?

Immediately after diagnosis, the baby will be admitted to the intensive care unit and placed on ventilation to help with breathing. Surgery is the go-to for all types of single ventricular defects, but prior to surgery, a few temporary treatments will be done to regulate blood circulation.

The most common surgery in babies with single ventricle defects is the Fontan operation, in which the baby’s surgeon will separate the heart into circulations for improved oxygenation of the blood. This will reduce the workload on the working ventricle and associated complications. If there is excess blood flow to the lungs, the surgeon may place a band around the pulmonary artery to restrict the flow.

Apart from surgery, the baby will also be placed on medication to assist heart function. Children with single ventricle defects will often need more than one surgery and regular check-ups to monitor and address possible infections, heart rhythm problems, fluid retention, and blood clots.

Conclusion:

Single ventricle defect is a birth defect that is typically diagnosed shortly after birth; most children with the defect will have at least an operation to repair the defect. Response to surgeries varies depending on factors like the type of defect and age at which the child undergoes surgery.

Dr. Yash Kathuria
Dr. Yash Kathuria

Family Physician

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