test 6 tetralogy of fallot Flashcards
Tetralogy of Fallot
■ Classically understood to involve four anatomical abnormalities
■ 10 % of all cyanotic heart defects,
– most common cause of blue baby syndrome
■ Very high association with Down’s Syndrome
Tetralogy of Fallot involves four heart defects
- (3 are congenital, 1 is acquired)
■ A large VSD
■ Pulmonary stenosis (RVOT obstruction)
■ An overriding aorta
- shifted anteriorly and to the right over the VSD stealing a lot of the flow
■ Right ventricular hypertrophy (RVH) (AQUIRED) - because of pulmonary obstruction
TOF Embryology
■ Aorta and PA start as a single tube (truncus arterosis) divided by the spiral septum
■ The spiral septum grows down and attaches to the ventricular septum which:
– Isolates the ventricles
– Isolates the aorta and the pulmonary artery
what if the spiral septum is not midline, but shifted towards the right side of the heart resulting in:
– The aorta opening to be large – pulmonary opening to be small – Spiral septum would miss the septum - TETRALOGY OF FALLOT - resulting in byanosis
What if the septum is not midline, but shifted towards the left side of the heart resulting in:
– The aorta opening to be small
– pulmonary opening to be large
– Spiral septum would miss the septum
- FATAL
Factors that increase the risk for TOF during pregnancy include
– Alcoholism in the mother – Diabetes – Mother > 40 years old – Poor nutrition during pregnancy – Rubella or other viral illnesses during pregnancy
TOF WITH Pulmonary Atresia
■ TOF with PA (pseudotruncus arteriosus) is a severe variant in which there is complete obstruction (atresia) of the right ventricular outflow tract (RVOT), causing an absence of the pulmonary trunk during embryonic development.
■ Blood shunts completely from the right ventricle to the left where it is pumped only through the aorta. The lungs are perfused via extensive collaterals from the systemic arteries, and sometimes also via the ductus arteriosus.
Pentalogy of Fallot
- TOF with the addition of an ASD
TOF: Blood Flow
■ Tetralogy of Fallot results in low oxygenation of blood due to the mixing of blood in the LV via the VSD and preferential flow of the mixed blood through the aorta (because of the obstruction to flow through the pulmonary valve)
- right to left shunt
■ In TOF w/ PA this R→L shunt is significantly worse
What might be the body’s response to the low saturations and decreased pulmonary blood flow?
- Elevate the hematocrit, it is not uncommon for these children to have hematocrits >50 %
TOF symptoms
■ The primary symptom is low blood oxygen saturation with or without cyanosis
■ If the baby is not cyanotic then it is sometimes referred to as a “pink tet”
■ Periods of severe hypoxic spells i.e. “tet spells”
■ Clubbing of fingers (skin or bone enlargement around the fingernails)
■ Difficult feeding/failure to gain weight
■ Passing out
■ Poor development
■ Squatting during episodes of cyanosis
Children having a TET spell symptoms
– Rapid, deep breathing. – Fainting/loss of consciousness. – Increasing blueness (cyanosis) of the lips, tongue and nailbeds – Irritability or uncontrolled crying.
Common Causes of TET spells
– Prolonged agitation and crying
– Stimuli (blood draw, bee sting, etc.)
– Decrease in SVR during potentiates a right to left shunt
What a child will do when dealing with Tet Spells
– Squatting and the knee chest position will increase aortic wave reflection
– Increases pressure on the left side of the heart, decreasing the right to left shunt (think clamping distal to outflow)
– thus decreasing the amount of deoxygenated blood entering the systemic circulation.
Palliative Surgery for TOF
– formed an anastomosis between the subclavian artery and the pulmonary artery
■ B-T Shunt
– Currently, Blalock-Thomas-Taussig shunts are not normally performed on infants with TOF except for severe variants such as TOF with pulmonary atresia (pseudotruncus arteriosus).
■ Central Shunt (ascending aorta to main pulmonary artery)
