MedicoPlexus
Contributing Authors:
Linus Kutup, Eric Hoffmeister, Benjamin Kersch, Niclas Samirae, Tobias Verdegem, Alexander Wolff, Lara Afaneh, Joana Strzlkowski, Nadine Fernandez, Katharina Weitzel
PART 2
41. Congenital heart defects with left to right shunt.
A left- to- right shunt means that oxygenated blood (from left side of circulation) manages to enter into the part of the circulation where usually only deoxygenated blood flows (right side of circulation) Thus, the deoxygenated blood simply becomes more oxygenated -> This does not result in cyanosis, this is why left to right shunts are also called ‘non-cyanotic shunts’. The major problem of left to right shunts is simply the increased volume load that results in the ‘right side’ of the circulation.
General characteristics of congenital heart disease with left-to-right shunt:
– The magnitude/ severity of the shunt depends on the location of the communication, its size and the ratio between the systemic and pulmonary vascular resistance/ pressure -> remember that the blood flow through a shunt is always from the site with higher pressure towards the site with lower pressure
– The consequences of increased blood flow to the lungs is the development of pulmonary overload with subsequent thickening in the pulmonary vessels (intima/media) -> narrowing of lumen -> increased pulmonary pressure -> pulmonary hypertension -> at some point the pressure in the right site of circulation becomes higher than the pressure on the left side and the shunts reverses to a right- to- left shunt (CYANOTIC) -> The reversion of blood flow direction through a shunt is known as EISENMENGER SYNDROME (AYZENMENGER SYNDROME)
– If the shunt is within the heart, we also get volume overload of the right heart in addition to the pressure overload from increased pulmonary resistance -> even worse
– The main clinical manifestation of left to right shunts is RIGHT SIDED HEART FAILURE!
🡪 Heart failure can be:
– acute: if the lesion is big -> HF occurs directly after birth because heart has no time to adapt to new circumstences (by hypertrophy,etc)
– chronic: if the lesion is small -> heart has time to adapt (hypertrophy,…) and patient may be asymptomatic (or only with weak symptoms of HF) until decompensation with dilatation results or until the shunt reverses.
– Symptoms of pulmonary hypertension and right sided heart failure:
– Pulmonary hypertension -> pulmonary edema -> less blood oxygenation -> tiredness, weakness and dyspnea, tachypnea and increased frequency of respiratory tract infections
– blood accumulates back into veins: edema in ancles, swollen neck veins, swollen liver, ascites,…
– Poor feeding, poor development, and failure to thrive
Types of Left-to-right shunts:
1) Atrial septal defects
2) Ventricular septal defects
3) Patent ductus arteriosus
Remember that before birth, these shunts are right- to- left shunts! After birth, pulmonary circulation starts which causes pressure changes -> the shunts become left-to right- shunts! After years, as heart undergoes hypertrophy etc the EISENMENGER SYNDROME may occur which reverses the shunts back to right- left- shunts daaaaaaaamn
1) Atrial septal defects:
– there are 3 major subtypes:
– Ostium primum atrial septal defect (often seen in Trisomie 21)
– ostium secundum atrial septal defect (watch the osmosis yotutube video about atrial septal defect and the difference between primum and secondum is well explained, it is hard to explain it in words)
– Sinus- venosus- defect (atrial defect + some pulmonary veins enter into right atrium and thus oxygenated blood from the lungs flows into the right side of circulation)
– Clinic:
The pathophysiology and amount of shunting depend on the size of the defect and the relative compliance of the both ventricles. Even with large ASDs and significant shunts, infants and children are rarely symptomatic.
– Diagnosis:
– Auscultation: A soft (grade I or II) systolic ejection murmur in the
region of the right ventricular outflow tract and a fixed split S2 are often audible (more blood in right atrium leads to more blood in right ventricle -> right ventricle needs more time to eject all the blood and thus pulmonary valve closes later than aortic valve and an additional S2 result)
– Ultrasound with Doppler shows the abnormal blood between the atria
– The ECG may show right axis deviation and right ventricular enlargement.
A chest radiograph may show cardiomegaly, right atrial enlargement, and a prominent pulmonary artery.
Treatment:
– Small-to-moderate–sized ostium secundum atrial septal defects diagnosed in the infant demonstrate significant likelihood of either spontaneous closure or reduction in size to the point that medical intervention no longer is indicated.
– Larger lesions may need surgical closure (e.g. with patch from pericardium)
2) Ventricular septal defect:
– The ventricular septum is a complex structure that can be divided into four components. 1) The largest component is the muscular septum. 2) The inlet or posterior septum comprises endocardial cushion tissue. 3) The subarterial or supracristal septum comprises conotruncal tissue. 4) The membranous septum is below the aortic valve and is relatively small.
– VSDs occur when any of these components fails to develop normally. VSD, the most common congenital heart defect, accounts for 25% of all congenital heart disease. Perimembranous VSDs are the most common of all VSDs (67%).
– The amount of flow crossing a VSD depends on the size of the defect and the pulmonary vascular resistance.
– Large VSDs are not symptomatic at birth because the pulmonary vascular resistance is normally elevated at this time (high pressure in right heart result-> high pressure in right heart cause a decrease in the pressure gradient between left and right heart and thus blood flow becomes less).
– As the pulmonary vascular resistance decreases over the first 6 to 8 weeks of life, the amount of shunt increases, and symptoms may develop.
Clinical Manifestations
– Small VSDs with little shunt are often asymptomatic but have a loud murmur.
– Moderate to large VSDs result in pulmonary overcirculation and heart failure.
Diagnosis:
– Auscultation: The typical physical finding with a VSD is a pansystolic murmur, usually heard best at the lower left sternal border. There may be a thrill. Large shunts increase flow across the mitral valve causing a mid-diastolic murmur at the apex. The splitting of S2 and intensity of P2 depend on the pulmonary artery pressure.
– ECG and chest x-ray findings depend on the size of the VSD. Small VSDs usually have normal studies.
– Larger VSDs cause volume overload to the left side of the heart (Why not right side???!!!), resulting in ECG findings of left atrial and ventricular enlargement and hypertrophy. A chest x-ray may reveal cardiomegaly, enlargement of the left ventricle, an increase in the pulmonary artery silhouette, and increased pulmonary blood
flow. Pulmonary hypertension due to either increased flow or increased pulmonary vascular resistance may lead to right ventricular enlargement and hypertrophy.
Treatment
– Approximately one third of all VSDs close spontaneously. Small VSDs usually close spontaneously and, if they do not close, surgery may or may not be needed (depends on severity).
3) Patent ductus arteriosus:
– Failure of the normal closure of ductus arteriosus (Botelli)
– With a falling pulmonary vascular resistance a couple weeks after birth, left-to-right shunting of blood and increased pulmonary blood flow occur.
Clinic:
– Symptoms depend on the amount of pulmonary blood flow.
– The magnitude/ severity of the shunt depends on the size of the PDA (diameter, length, and tortuosity) and the pulmonary vascular resistance.
– Small PDAs are asymptomatic; moderate to large shunts can produce the symptoms of heart failure as the pulmonary vascular resistance decreases.
Diagnosis:
– The physical examination findings depend on the size of the shunt. A widened pulse pressure is often present as a result of the runoff of blood into the pulmonary circulation during diastole. A continuous, machine-like murmur can be heard
at the left infraclavicular area, radiating along the pulmonary arteries and often well heard over the left side of the back. Larger shunts with increased flow across the mitral valve may result in a mid-diastolic murmur at the apex and a hyperdynamic
precordium. Splitting of S2 and intensity of P2 depend on the pulmonary artery pressure.
– X-ray: Moderate to large shunts may result in a full pulmonary artery silhouette and increased pulmonary vascularity. ECG findings vary from normal to evidence of left ventricular hypertrophy. If pulmonary hypertension is present, there is
also right ventricular hypertrophy.
Treatment:
– Spontaneous closure of a PDA after a few weeks of age is uncommon in full-term infants.
– Moderate and large PDAs may be managed initially with diuretics, but eventually
require closure.
– Elective closure of small, hemodynamically insignificant PDAs is controversial.
– Most PDAs can be closed in the catheterization laboratory by either coil embolization
or a PDA closure device.
4) There are also atrio-ventricular septal defects -> defect is present in the atrial septum and the ventricular septum…..
BARE IN MIND THAT SYMPTOMS OF LEFT TO RIGHT SHUNTS TAKE SOME WEEKS TO OCCUR BECAUSE AT THE BEGINNING OF LIVE, THE PULMONARY PRESSURE IS STILL QUITE HIGH AND THUS THERE ARE HIGH PRESSURES IN THE RIGHT HEART AS WELL. THIS MAKES IT ‘DIFFICULT’ FOR THE BLOOD TO FLOW FROM LEFT TO RIGHT HEART. AS THE PULMANORY PRESSUERE DECREASES AFTER A FEW WEEKS, BLOOD FLOW FROM LEFT TO RIGHT OCCURS MORE READILY AND SYMPTOMS OCCUR
42. Congenital heart defects with right to left shunt.
Right- to- left shunt means that deoxygenated from the right side of the circulation manages to enter into the oxygenated blood on the left side of the circulation -> the result is a lower oxygen concentration in the blood (Hypoxemia) -> deoxygenated haemoglobin is much darker than oxygenated Hb and it makes our skin appear blue -> CYANOSIS!
The most common cyanotic congenital heart defects are the five Ts:
- Tetralogy of Fallot
- Transposition of the great arteries
- Tricuspid atresia
- Truncus arteriosus
- Total anomalous pulmonary venous return
– While in the previous point (left-to-right shunt) the volume- and pressure overload were the major problem, in the case of right-to-left shunts it is the hypoxemia that is the major problem (the left heart can handle the volume-and pressure overload much better)
– Additional symptoms (if lesion is severe enough) could be poor feeding, poor development, and failure to thrive
1) Tetralogy of Fallot:
– Tetralogy of Fallot is the most common cyanotic congenital heart defect
– There are four structural defects:
a) Pulmonary valve stenosis
b) Right ventricular hypertrophy (due to the pulmonary stenosis?!)
c) Ventricular septal defect (VSD)
d) overriding aorta (the ventricular
septal defect is located in such a way
that the right ventricle directly pumps
deoxygenated blood through the defect
into the aorta)
There are actually 2 subtypes of tetralogy of fallot, depending on the severity of the stenosis and the hypertrophy of the right ventricle!
1) Non-cyanotic type: The stenosis and the hypertrophy are not very severe and thus the pressure in the right ventricle remains smaller than in the left ventricle -> the VSD results in right- to- left shunt (so actually this type is acyanotic and does not belong to this syllabus point) -> This type can develop into the cyanotic type over time as hypertrophy gets worse and worse
2) Cyanotic type: much more important for us: the hypertrophy and the stenosis are severe -> they result in a high pressure in the right ventricle -> the pressure in right ventricle is higher than in the left ventricle and thus the VSD leads to a right-to-left shunt! This is uncommon for a VSD!!!
Clinical Manifestations
– Infants initially may be acyanotic (they get cyanotic as the hypertrophy becomes worse and the shunts reverses into a right to left shunt)
– A pulmonary stenosis murmur is the usual initial abnormal finding.
– The amount of right-to-left shunting at the VSD (and the degree of cyanosis) increases as the degree of pulmonary stenosis increases.
– With increasing severity of pulmonary stenosis, the murmur becomes shorter and softer.
– In addition to varying degrees of cyanosis and a murmur, a single S2 and right ventricular impulse at the left sternal border are typical findings.
– When hypoxic periods (Tet spells) occur, they are usually progressive. During aTet spell, the child typically becomes restless and agitated and may cry inconsolably. An ambulatory toddler may squat -> Squatting compresses arteries in knee and hip -> peripheral resistance and pressure rise -> pressure in left ventricle rises which makes it harder for the blood to flow from right to left ventricle and thus the shunt becomes less severe -> less deoxygenated blood enters into systemic circulation and symptoms get better!!!
– Hyperpnea occurs with gradually increasing cyanosis and loss of the murmur.
– In severe hypoxic periods, prolonged unconsciousness and convulsions, hemiparesis, or death may occur.
– Independent of hypoxic peridos, patients with unrepaired tetralogy of Fallot are at increased risk for cerebral thromboembolism and cerebral abscesses resulting, in part, from their right-to-left intracardiac shunt.
Diagnosis:
The ECG usually has right axis deviation and right ventricular hypertrophy. The classic chest x-ray finding is a boot-shaped heart created by the small main pulmonary
artery and upturned apex secondary to right ventricular hypertrophy.
Echocardiography shows the anatomic features, including the anatomic level and quantification of pulmonary stenosis.
Treatment:
The natural history of tetralogy of Fallot is progression of pulmonary stenosis and cyanosis. Treatment of hypoxic periods consists of oxygen administration and placing the child in the knee-chest position (to increase venous return-> I don’t get that). Traditionally, morphine sulfate is given (to relax the pulmonary infundibulum and for sedation).
– If necessary, the systemic vascular resistance can be increased acutely through the administration of an α-adrenergic agonist (phenylephrine).
The occurrence of a cyanotic spell is an indication to proceed with surgical repair.
– Complete surgical repair with VSD closure and removal or patching of the pulmonary stenosis can be performed in infancy.
2) Transposition of the great vessels:
– the aorta arises from the right ventricle and the pulmonary artery arises from the left ventricle -> CRAZY!!!
– This results in desaturated blood returning to the right side of the heart and being pumped back out to the body, while well-oxygenated blood returning from the lungs enters the left side of the heart and is pumped back to the lungs -> Basically, we get 2 individual circulations that do not communicate with each other -> The first circulation is from the left ventricle -> then pulmonary artery and lungs -> then left atrium -> then left ventricle again -> blood gets oxygenated but it does not get pumped though the body! The second circulation is from right ventricle into aorta, then systemic circulation all over body -> then right atrium -> then right ventricle again -> blood gets pumped though the body but never gets oxygenated
– Without mixing of the two circulations, death occurs quickly.
– Mixing can occur at the atrial (patent foramen ovale/atrial septal defect [ASD]), ventricular [VSD], or great vessel (patent ductus arteriosus [PDA]) level -> we can give prostaglandins to keep ductus arteriosus open 😉
Clinical Manifestations:
– A history of cyanosis is always present, although it depends on the amount of mixing. – Quiet tachypnea and a single S2 are typically present. If the ventricular septum is intact, there may be no murmur.
– Children with transposition and a large VSD have improved intracardiac mixing and less cyanosis. They may present with signs of heart failure. The heart is hyperdynamic, with palpable left and right ventricular impulses. A loud VSD murmur is heard. S2 is single.
Diagnosis:
ECG findings typically include right axis deviation and right ventricular hypertrophy because the right ventricle has to pump blood into the systemic circulation, where the pressure is much higher than in the pulmonary circulation (into which the right ventricle usually pumps)
– Echocardiography shows the transposition of the great arteries, the sites and amount of mixing, and any associated lesions.
Treatment:
Initial medical management includes prostaglandin E1 to maintain ductal patency. If significant hypoxia persists on prostaglandin therapy, a balloon atrial septostomy improves mixing between the two circulations. Complete surgical repair is most often an arterial switch.
3) Truncus arteriosus communcians:
– It results from the failure of septation (septum growth) of the truncus arteriosus during the first 3 to 4 weeks of gestation -> at the beginning, it is normal that the left and the right ventricle both pump blood into one big shared vessel -> Usually, a septum develops and the vessel separates to form the aorta and the pulmonary artery -> this failed to occur here!!
– A single arterial trunk arises from the left and the right ventricle with a large VSD immediately below the truncal valve. The pulmonary arteries arise from the single arterial trunk either as a single vessel that divides or individually from the arterial trunk to the lungs.
Clinical Manifestations
– Varying degrees of cyanosis depend on the amount of pulmonary blood flow.
– If not diagnosed at birth, the infant may develop signs of heart failure as pulmonary vascular resistance decreases after a few weeks
– The signs then include tachypnea and cough. Peripheral pulses are usually bounding as a result of the diastolic runoff into the pulmonary arteries.
– A single S2 is due to the single valve. There may be a systolic ejection click, and there is often a systolic murmur at the left sternal border.
Imaging Studies
– ECG findings include combined ventricular hypertrophy and cardiomegaly.
– A chest x-ray usually reveals increased pulmonary blood and may show displaced pulmonary arteries.
– Echocardiography defines the anatomy, including the VSD, truncal valve function, and origin of the pulmonary arteries.
Treatment:
Medical management is usually needed and includes anticongestive medications. Surgical repair includes VSD closure and placement of a conduit between the right ventricle and pulmonary arteries.
I don’t know how important this is:
4) Total anomalous pulmonary venous return:
Disruption of the development of normal pulmonary venous drainage during
the third week of gestation results in one of four abnormalities. All of the pulmonary veins fail to connect to the left atrium and return abnormally via the right side of the heart. They may have supracardiac, infracardiac, cardiac, or mixed drainage. An atrial-level communication is required for systemic cardiac output and survival.
Management: At surgery, the common pulmonary vein is opened into the left atrium, and there is ligation of any vein or channel that had been draining the common vein
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