CONGENITAL HEART DISEASE: AN INTRODUCTION

The Heart

The heart is arguably one of the body’s most vital organs. Primarily made of muscle, the heart pumps blood to supply all other organs. The heart contributes to the circulation of much-needed oxygen by pumping blood into the lungs, receiving this oxygenated blood, and pumping it out again to the rest of the body. This continuous movement allows blood to distribute nutrients and collect waste products to and from cells.

The Heart and Blood Circulation

The heart is essentially a pump that receives and distributes blood through two main types of blood vessels, arteries, and veins. There are two main sides, the left and the right. Each side is composed of two chambers and a valve that separates them. Towards the center, two other valves facilitate the transfer of blood to the lungs and to the rest of the body.

Unoxygenated blood enters the heart from major veins into the first chamber on the right side, called the right atrium. This flows through the tricuspid valve into the second chamber, known as the right ventricle. This chamber contracts to push blood through the pulmonary valve, the pulmonary artery, and into the lungs.

After blood receives oxygen in the lungs, they return to the heart via veins connected to the first chamber on the left side, called the left atrium. This flows through the mitral valve into the second chamber, known as the left ventricle. This chamber pumps blood through the aortic valve into the aorta, for distribution to all other organs.

Blood from the heart arrives in blood vessels called arteries. These vessels branch off and become smaller (arterioles), eventually developing into microscopic vessels called capillaries. These special vessels release oxygen and nutrients, while receiving carbon dioxide and waste products. Blood moves on into small vessels called venules, which combine to form veins, ultimately entering the heart once again to repeat the cycle.

Congenital Heart Disease

While heart diseases are more commonly acquired throughout the years in adult life, occasionally they may develop even before a child is born. These are called congenital heart defects (CHDs) and are often due to a problem with the heart’s anatomy. When they have a significant effect on a child’s health or growth, they are called congenital heart diseases.

Statistics / Epidemiology

For every 1,000 newborns, eight are born with a congenital heart defect (around 0.8% of all live births). The incidence is higher in children born prematurely (2% or 20 for every 1,000 newborns). Of these children, 25% would have a severe or critical form of CHD. Unfortunately, congenital heart defects are the leading cause of death in all children who have any type of congenital malformation. The most common types of CHDs are ventricular septal defect (VSD), atrial septal defect (ASD), and patent ductus arteriosus (PDA).

Causes

The main cause of CHD is largely unknown. Some types are linked with genetics, particularly in chromosomes. Experts consider CHDs to be multifactorial - a combination of factors from genes, the environment, and the mother’s health during pregnancy.

Children diagnosed with certain conditions, such as DiGeorge syndrome, Alagille syndrome and Williams syndrome, are more prone to having CHDs. Mothers who were diagnosed with diabetes or obesity, or have smoked during pregnancy, risk the development of CHDs in their unborn child.

General Classification

The most common classification of congenital heart defects lies in the presence or absence of cyanosis (a bluish discoloration of the skin). These CHDs are further classified based on other findings from a physical exam and appropriate imaging studies.

Not all children with CHDs are cyanotic, and not all cases are detected immediately after birth. Severe types may already be diagnosed on a fetal ultrasound, even before the child is born. The specific anatomy of a defect determines how serious a condition may be. Some defects may make it possible for a child to look completely normal at birth; most of these CHDs are benign and do not present with cyanosis. A few present with normal findings at birth, but progress to show symptoms after weeks or even months. On the other hand, children with critical CHDs may have an acceptable route of blood circulation inside their mother’s womb but are in distress immediately after birth. Lastly, several types of CHDs can resolve on their own, while others may either become smaller or bigger as a child grows.

Early Screening

Most hospitals and medical centers provide initial screening for critical congenital heart defects before a newborn is discharged. This simple test is known as pulse oximetry, done once or twice at the first or second day of life. It is not a 100% accurate test, but it significantly filters out children who are at risk of severe CHDs. Because of this, mild to moderate cardiac defects may not be detected with the pulse oximetry test.

The pulse oximeter is usually a small machine with a sensor attached to a wire. The sensor is simply wrapped around a child’s finger to determine the amount of oxygen in the blood. A “pass” result means that there are adequate levels of oxygen in the blood, while a “fail” result means insufficient oxygen. An initial “fail” result should have repeat testing, or may warrant further screening with other tests, such as an ultrasound of the heart (called an echocardiogram).

Summary

The heart plays a critical role in transporting blood, oxygen, nutrients, and waste products across the body. Some children may develop anatomical defects in this muscular pump, which can cause decreased oxygen levels in the body, a definite impact on a child’s growth and development. Initial screening is done at the first few days of life to determine which infants may have critical heart defects.

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References:

• Costanzo, L.S. (2014). Chapter 4: Cardiovascular Physiology. Physiology, 5th edition. Saunders, Elsevier.
• Kliegman, R.M. et al. (2020). Part XIX The Cardiovascular System. Nelson Textbook of Pediatrics 21st edition. Elsevier.
• Congenital Heart Defects (2020). National Center on Birth Defects and Developmental Disabilities, Centers for Disease Control and Prevention. Taken from: https://www.cdc.gov/ncbddd/heartdefects/facts.html
• Critical Congenital Heart Defects (2020). National Center on Birth Defects and Developmental Disabilities, Centers for Disease Control and Prevention. Taken from: https://www.cdc.gov/ncbddd/heartdefects/cchd-facts.html

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