Congenital heart defects - Cyanotic: Nursing

Congenital heart defects are cardiac conditions and anomalies that are present at birth. These are usually divided into two categories based on the presence or absence of cyanosis, which means bluish discoloration of the skin. The main types of cyanotic heart defects are tetralogy of Fallot, or ToF for short, which is the most common one; in addition to transposition of great vessels, or ToGV; tricuspid atresia; as well as persistent truncus arteriosus, or PTA; and total anomalous pulmonary venous return, or TAPVR. 

Now, let’s quickly recap the anatomy and physiology of fetal circulation. During fetal life, the lungs are filled with fluid and have high vascular resistance, so they don’t participate in gas exchange. Instead, the placenta serves as the organ of gas exchange, as well as delivering nutrients and removing metabolic wastes from the fetus.  

So, oxygenated blood flows from the uterine arteries into the placenta, where oxygen passes through the capillaries and into the umbilical vein.  

Then, part of the blood reaches the fetal liver, whereas about half of it bypasses the liver by a shunt called the ductus venosus, which diverts the oxygenated blood into the inferior vena cava, which has deoxygenated blood from the lower body.  

Then, this blood flows into the right atrium and further mixes with deoxygenated fetal blood coming from the brain and upper body through the superior vena cava. Most of this mixed blood then moves through a small flap called the foramen ovale directly into the left atrium, into the left ventricle, and through the ascending aorta into the systemic circulation, supplying oxygen to the brain and upper body, as well as the lower body.  

The rest of the blood from the right atrium flows into the right ventricle, and into the pulmonary arteries. A small amount of this blood moves into the pulmonary circulation and perfuses the lung tissue, but most of it is shunted through the ductus arteriosus back into the aorta and systemic circulation.  

Ultimately, the blood flows from the systemic circulation into the umbilical arteries, and then back to the placenta.  

At birth, when the umbilical cord is cut, the baby stops receiving oxygenated blood from the placenta. As a result, the baby’s blood has a reduction in oxygen levels, and an increase in its carbon dioxide levels. This change stimulates the respiratory center in the baby’s brain, which stimulates the newborn to take their first breath, along with temperature changes and tactile stimulation in the extrauterine environment.

This prompts a series of changes, which include lung expansion and decreased pulmonary vascular resistance, allowing increased blood flow to the lungs.  

In addition, there’s a functional closure of the foramen ovale and ductus arteriosus.  

With time, the ductus venosus, ductus arteriosus, the umbilical arteries, and the umbilical vein atrophy and convert into ligaments.   

Now, the exact cause of congenital heart defects is unknown, but it's believed to be associated with risk factors that can interfere with the development of the heart. These risk factors include chromosomal abnormalities of the fetus, in addition to maternal infections, chronic illnesses. and exposure to teratogens. The list of teratogens is long, and it includes things like medications such as isotretinoin, alcohol, recreational drugs like cocaine, tobacco smoke, and heavy metals like mercury. 

The pathology of cyanotic congenital heart defects starts when a cardiac structure fails to form or close properly. The main types of cyanotic heart defects are tetralogy of fallot, or ToF for short, transposition of great vessels, or ToGV, tricuspid atresia, as well as persistent truncus arteriosus, or PTA, and total anomalous pulmonary venous return, or TAPVR.  

So, in tetralogy of Fallot or ToF, there are four heart abnormalities: pulmonary stenosis, which is narrowing of the pulmonary valve; right ventricular hypertrophy, which is enlargement of the right ventricle; ventricular septal defect, which is a gap in the ventricular septum that separates the right and left ventricles; in addition to overriding aorta where the aorta is shifted and sits above the ventricular septal defect.  

So the result is oxygen rich blood and oxygen poor blood in the right and left ventricle mix due to the ventricular septal defect, and then it’s pumped out of the overriding aorta.   

Next is transposition of the great arteries, or TGA, where the aorta and the pulmonary trunk swap locations. When this occurs, oxygen poor blood returning to the right side of the heart is pumped into the aorta and the rest of the body instead of the pulmonary artery and the lungs.  

With tricuspid atresia, the tricuspid valve that normally prevents blood from returning into the right atrium when the right ventricle contracts, is malformed or fails to develop entirely. Because of this, oxygen poor blood returning to the right atrium can not enter the right ventricle, so an atrial septal defect is needed to mix the blood in the right and left atrium, and a ventricular septal defect is needed for the blood to mix in the right and left ventricle.   

Next is persistent truncus arteriosus, where the truncus arteriosus doesn't split properly into the aorta and pulmonary artery during fetal development.  So this extra large vessel sits above both ventricles and allows deoxygenated blood and oxygenated blood to mix before getting pumped to the lungs and the rest of the body.  

Finally, there’s total anomalous pulmonary venous return , or TAPVR, in which all four pulmonary veins form abnormal connections.  

So instead of returning blood from the lungs to the left atrium, they connect to the right atrium, the superior vena cava or inferior vena cava.  

The result is that oxygen rich blood from the lungs returns to the right side of the heart, where it’s pumped back to the lungs.  

The condition is only compatible with life if there’s an atrial septal defect that allows some of the blood in the right atrium to flow into the left atrium where it could eventually be pumped into systemic circulation.   

Regardless of the type of defect, the blood being pumped out of the heart does not contain enough oxygen to adequately supply the body tissue, leading to cyanosis.  

In terms of complications, the persistence of deoxygenated blood in systemic circulation can progress to chronic hypoxia, to which the body responds by producing more red blood cells, called polycythemia. The heart can also fail to pump enough oxygenated blood to the tissues, resulting in heart failure. At the same time, if the oxygen supply to the brain gets so low, it may result in a cerebrovascular accident, or CVA for short.  

Other complications of cyanotic heart defects include arrhythmias, embolism, and infective endocarditis, brain abscess formation, pulmonary vascular disease, and even death.  

Clinical manifestations of cyanotic heart defects mainly include cyanosis, which is typically present at birth or within the first few weeks of life. This is often joined by lethargy, tachycardia, tachypnea, activity intolerance, as well as clubbing of fingers and toes. Some clients may also experience feeding problems, which may lead to poor weight gain, and failure or difficulty to thrive. 

Clients with Tetralogy of Fallot, can have acute and severe cyanotic episodes, called “Tet spells”.  

This is where activities like feeding, exercise, or crying, cause spasm of the infundibular septum which worsens the stenosis and increases the obstruction to pulmonary blood flow. This is called right ventricular outflow tract obstruction and results in increased right to left shunting, eventually decreasing the blood flow through the lungs, causing a fall in arterial oxygen saturation. The lack of oxygen causes tachypnea or rapid abnormal breathing; and increases the activity of the sympathetic nervous system, eventually increasing heart contractility and even more obstruction of the right ventricular outflow tract. As a result, cyanosis occurs.  

Additionally, clients undergoing a tet spell can be seen squatting or assuming a fetal position. This position increases the peripheral vascular resistance by kinking the femoral artery, which improves the pulmonary blood flow and relieves the client.