Cyanotic congenital heart defects: Pathology review

Chapters:

Watch video only

Case Study0:00–0:34

At the pediatric cardiology clinic, two mothers were chatting about their kids. One mom spoke about a five year old boy named Blake who was a bluish color at birth and had a continuous machine like heart murmur between the scapulas.
Another mom spoke about her 12 year old son, Paul, who was healthy at birth. But when he was breastfeeding or crying, his skin turned pale and then blue as a child, Paul got out of breath easily and needed to squat down to recover.
And during his school physical, he was found to have a heart murmur. Both Blake and Paul have cyanotic congenital heart defects or C hds, which usually start causing problems within the 1st 3 to 8 weeks of life.

Pathology0:34–1:53

They can be broadly grouped into lifethreatening cyanotic heart defects or the less dangerous acyanotic heart defects. Let's go over five of the life threatening cyanotic congenital heart defects, persistent truncus, arteriosus transposition of the great vessels, tetralogy of fallot total anomalous pulmonary venous return and tricuspid atresia.
Now, the first three are caused by outflow tract defects that develop during the formation of the aorta and pulmonary artery.
In fetal development. The heart looks like a long tube.
The top part is the truncus arteriosus and the part inferior to that is the bulbous cordis. Neural crest cells migrate to the bulbs, cordis and trigger the formation of the aorticopulmonary septum.
This structure is formed when two endocardial cushions appear on the right, superior and left inferior walls. These grow like a spiral, imagine a corkscrew and they wrap around each other forming a single septum that divides the truncus into the roots of the aorta.
One root connects to the primitive left ventricle. The other connects to the pulmonary artery and primitive right ventricle.
That's how blood gets routed to the right place. Ok.

Pers. Truncus Arteriosus1:53–2:30

So if the aorticopulmonary septum doesn't form or forms incompletely, the result is a persistent truncus arteriosis for your exams.
It's important to know that this is caused by the failure of neural crest cells to properly migrate to the bulbous cordis.
So we end up with a single vessel that's connected to both the left and right ventricle, allowing oxygenated blood and deoxygenated blood to mix this large common trunk eventually divides into the aorta and the pulmonary artery and both carry partially oxygenated blood.
When the partially oxygenated blood goes out to the body, it causes cyanosis. Ok.
Moving on. If the spiraling of the aortic or pulmonary septum doesn't occur at all, we get transposition of the great vessels where the aorta connects to the right ventricle and the pulmonary artery connects to the left ventricle here, deoxygenated blood from the systemic circulation goes to the right side of the heart and gets pumped out of the aorta.

Transposi. Great Vessels2:30–3:20

Again. Meanwhile, oxygenated blood from the lungs, goes to the left side of the heart and gets pumped back to the lungs.
So for the test, remember that we end up with two separate closed systems. Another high yield fact is that the only way that a newborn can survive is with a patent ductus arteriosus or PDA.
A, an opening between the aorta and pulmonary artery that allows some of the oxygenated and deoxygenated blood to mix. But since the PDA normally closes soon after birth, it has to be kept open to keep the newborn alive.
Now, there's tetrology of fallot which is the most common cyanotic congenital heart defect. And tetrology refers to four main features that you absolutely have to remember.

Tetralogy of Fallot3:20–5:08

First, a part of the right ventricle wall under the outflow tract called the infundibular septum is displaced anteriorly which narrows the right ventricular outflow tract leading to pulmonary stenosis.
Second, the narrowing of the right ventricular outflow tract increases resistance to blood flow. So the myocardium of the right ventricle hypertrophy to overcome that resistance.
On X ray, the enlarged heart looks like a boot. Third, there's a V sda tiny hole between the ventricles that allows blood to shunt across initially, the left sided pressures are higher.
So blood flows to the right, but over time, right sided pressures get. So high that blood flows to the left.
This is called Eisenmenger syndrome, which is very important to remember. In other words, some of the deoxygenated blood bypasses the lungs and goes to the left ventricle fourth, there's a displaced aorta that sits right above the ventricular septal defect.
And this is called an overriding aorta. A key concept that's frequently tested is that the level of cyanosis depends on the severity of pulmonary stenosis.
So, unlike other cyanotic CHD S, some newborns are asymptomatic until later in life, like in the case of Paul. But these infants can have cyanotic episodes called tet spells.
And remember for your exams that this is when actions like feeding or crying cause the spasms of the infundibular septum which worsens the stenosis and causes cyanosis.
If a person with tetralogy of fallot squats down, it kinks the arteries in the legs which increases peripheral vascular resistance, increasing afterload, that leads to less blood shunting to the left ventricle and more blood going through the pulmonary artery instead.
Ok. Moving on the next two disorders are not outflow tract defects.

TAPVR5:08–5:58

First, there's total anomalous pulmonary venous return or T A PVR. Normally the four pulmonary veins develop close to the lungs and then grow towards the heart to fuse with the left atrium.
The main concept you'll need to know is that in tap PVR, the pulmonary veins fuse at the wrong location, usually in the right atrium or in systemic veins.
This means oxygenated blood from the lungs ends up on the right side of the heart. So, in order for the fetus to survive, an ASD is needed to allow blood to move from the right atrium to the left atrium and then into the left ventricle and out to the body.
Since the right side of the heart receives a lot of extra blood, pulmonary hypertension usually develops. Meanwhile, the blood that's pumped to the rest of the body is a mixed, partially saturated blood.
So there's cyanosis, the final CHD is tricuspid atresia. And that's where the tricuspid valve is malformed or fails to develop entirely if it's absent, deoxygenated blood returning from systemic circulation, gets trapped in the right atrium and can't reach the lungs.

Tricuspid Atresia5:58–6:38

The important fact to remember for exams is this is incompatible with life unless there's an ASD which allows blood to reach the left atrium and then A VSD which allows blood to reach the right ventricle.
So it can be pumped to the lungs to make matters worse. The roundabout path severely limits the amount of blood that reaches the right ventricle.
So it atrophies, both the mixing of blood and the decreased pulmonary blood flow contribute to cyanosis. Now, all five C hds share some common symptoms.

Diagnosis6:38–8:03

First, there's cyanosis which is typically present at birth or within the first few weeks of life. The exception is tetrology of fallot where the cyanosis might not appear until later in life.
Peripheral cyanosis is mild cyanosis in the limbs and it's normal in newborns. Central cyanosis is where the infant's whole body is cyanotic and it's abnormal and should always be investigated.
Other symptoms of CHD S are difficulty feeding and failure to thrive CHD S can be detected prenatally via ultrasounds. After birth, pulse, oximetry, ecg and chest x rays can be done.
But on a test, the best answer choice for confirming ACH D is with an echocardiogram. Now, it's also important to remember the heart murmurs that are frequently associated with the C hds.
Since they might be the best clues you get on an exam. Since tetrology of fallot and tricuspid atresia often have VSD, there can be a holosystolic heart murmur at the left, lower sternal border, tricuspid atresia and T A PVR are associated with an ASD.
So there's a systolic ejection murmur at the left upper sternal border. Transposition of the great vessels can occur alongside A VSD ASD or PDA, which presents as a continuous machine like murmur at the left infraclavicular area or between the scapulae for Blake and Paul Blake was cyanotic at birth and he had a PDA murmur which could be auscultated at the back.

Summary8:03–8:31

So he most likely had transposition of the great vessels. Meanwhile, Paul probably had a mild tetralogy of fallot since he was not cyanotic at birth and he experienced tet spells.
Another clue is that he got symptomatic relief from squatting down which increased the afterload and thus decreased the left or right shunting and increased pulmonary blood flow.
And that's the pathology in a nutshell.
Cyanotic congenital heart defects: Video, Anatomy | Osmosis