Tetralogy of Fallot

Question 1

the four defects of tetralogy of fallot

Answer 1

ventricular septal defect
pulmonary stenosis
overriding aorta
right ventricular hypertrophy

Question 2

the three anatomical defects are

Answer 2

ventricular septal defect
pulmonary stenosis
overriding aorta

Question 3

the one physiological defect is

Answer 3

right ventricular hypertrophy

Question 4

tetralogy of fallout is also called

Answer 4

blue baby syndrome

Question 5

some other congenital abnormalities that may be associated with tetralogy of fallot

Answer 5

right aortic arch
abnormal coronary artery anatomy
pulmonary atresia
aorticopulmonary collateral vessels
patent ductus arteriosus
atrioventricular septal defect
atrial defect
absent pulmonary valve

Question 6

development of tetralogy of fallot

Answer 6

normally, the truncus arteriosus is split in two by the evolving spiral septum

in tetralogy of fallot, the truncus arteriosus fails to divide
the spiral septum cannot fuse with the growing muscular ventricular septum, causing a ventricular septal defect.

there is narrowing of the pathway from the right ventricle to the pulmonary artery which causes pulmonary artery stenosis

the aortic root is enlarged and extends over the right ventricle outflow tract causing the overring aorta

right ventricular hypertrophy occurs as a physiological adaptation to increased afterload in the heart

Question 7

fetal circulation

Answer 7

circulating blood bypasses the lungs
fetal blood is shunted from the right atrium to the left atrium via the foramen ovale
oxygenated blood moves from the left atrium to the left ventricle and into the aorta and the body
when deoxygenated blood returns from the body it enters the right atrium and flows into the right ventricle
in the fetus, the blood bypasses thee lungs and flows through the ductus arteriosus in the descending aorta
the descending aorta collects to the umbilical arteries nd the deoxygenated blood flows back to the placenta

Question 8

the feto-maternal interface

Answer 8

deoxygenated blood is oxygenated again in the feto-maternaal interface
the oxygenated blood travels across the placenta into the foetus’ right atrium

Question 9

normal conversion to lung use

Answer 9

when a bby takes the first breath, the lungs expand reducing resistance to blood flow and allowing for more flow from the right ventricle
the ductus arteriosus and formane ovale close

Question 10

what happens when a baby with tetralogy of fallot is born

Answer 10

1. ventricular septal defect allows the mixing of oxygenated and deoxygenated blood
   some deoxyganted blood is pumped to the body resulting in cyanosis
2. overriding aorta means that the aortic valve is placed further to the right than normal, above the VSD. when the right ventricle contracts, the aortic valve is in the path of the blood, so deoxygenated blood enters the aorta from the right side of the heart
3. pulmonary stenosis means there is greater resistance to the flow of blood from the right ventricle into the pulmonary artery, causing blood to preferentially be pushed through the VSD
4. the right ventricle is pumping blood into the pulmonary artery under great resistance due to pulmonary stenosis, and due to the pressures from the left ventricle being transferred to the right ventricle through the VSD. this puts increased strain on the right ventricle causing right ventricular hypertrophy

Question 11

the degree of cyanosis is related to

Answer 11

the severity of the pulmonary stenosis

Question 12

risk factors for tetralogy of fallot include

Answer 12

1st degree family history of congenital heart disease
a parent with tetrology of fallot
a parent with DiGeorge syndrome
foetal exposure to teratogens in utero (eg. alcohol, warfarin, and trimethadone)
- poorly controlled materal diabetes
- maternal intake of retinoic acid
- congenital rubella infection
- increaased maternal age (over 40 years old)

Question 13

subtypes of tetrology of fallot

Answer 13

clinical features vary depending on subtype
1. TOF with a milder form of pulmonary stenosis
2. TOF with pulmonary atresia
3. TOF with absent pulmonary valve

Question 14

TOF with a milder form of pulmonary stenosis

Answer 14

usually asymptomatic about birth
as the child and the heart grows, the symptoms develop
around age 1-3 years, the child develops cyanosis

Question 15

TOF with pulmonary atresia

Answer 15

present in the first few weeks of life with cyanosis and respiratory distress

Question 16

TOF with absent pulmonary valve

Answer 16

the pulmonary valve is markedly dysplastic and its effectively regurgitant to a moderate or severe degree
this causes enlargement of the branch pulmonary arteries as well as the right ventricle

Question 17

typical findings on general examination of tetrology of fallot

Answer 17

central cyanosis
clubbing
respiratory distress
thrill
heave (due to right ventricular hypertrophy)
an ejection systolic murmur loudest in the 2nd intercostal space, left upper sternal edge
ejection click due to the closuure of the dilated aortic valve in diastole
single S2 due to closure of the aortic valve in diastole with reduced pulmonary valve closure due to PA stenosis
continuous murmur at the left upper sternal edge if there is patent ductus arteriorus

Question 18

differential diagnosis of tetrology of fallot

Answer 18

other types of cyanotic congenital heart disease (6 Ts of cyanotic congenital heart disease)
- Transposition of the great arteries
- Total anomalous pulmonary venous drainage
- Tetrology of fallot
- Truncus arteriosus
- Tricuspid valve abnormalities
- Ton of others: hypoplastic left heart syndrome , VSD with eisenmenger syndrome

Question 19

how is tetrology of fallot usually identified

Answer 19

during antenatal screening
a foetal echocardiogram
during a newborn baby check, an ejection systolic murmur caused by pulmonary stenosis may be heard

Question 20

relevant bedside investigations include

Answer 20

pulse oximetry
ECG: to detect heart chamber enlargement and arrythmia
TOF may present with right axis deviation and right ventricular hypertrophy

Question 21

TOF on chest x-ray

Answer 21

to visualise structure of the heart and lungs
findings may include a boot shaped heart due to right ventricular hypertrophy
or reduced ppulomnary vascular markings due to reduced pulmonary blood flow

Question 22

TOF on cardiac catheterisation

Answer 22

used to evaluate the structure and haemodynamic physiology of the heart and help to plan for surgery
cardiac catheterisation may also be used to deliver therapy such as stent angioplasty of the ductus arteriosus, or stent angioplasty to the right ventricular infundibulum in babies who exhibit hypercyanotic spells

Question 23

acute management before surgery

Answer 23

some patients are given prostaglandins infusion to maintain a patent ductus ateriosus
this allows blood flow from the aorta to travel to the lungs which may be necessary when there is not enough blood flow from the heart through the pulmonary valve into the lungs

Question 24

surgical bridging procedures

Answer 24

used in infants with poor pulmonary artry anatomy or co-morbidities who are not suitable to undergo surgical repair immidiately
used to help relive cyanosis and defers the meed for complete surgical repair
called a Black-Taussing shunt

Question 25

Blalock tuassing shunt

Answer 25

usually performed in the first week of life as a form of intermediate management until complete repair can be conducted
the BT shunt mimics a patent ductus arteriosus and increases pulmonary blood flow

Question 26

two ways of doing a BT shunt

Answer 26

1. anastomosis of the subclavian artery to the pulmonary artery - allows more blood to be pumped to the lungs as the high-pressure arterial system forces blood through the lungs
2. modified BT shunt: artificial shunt made form synthetic material