Tetralogy of Fallot Background

TOF Characteristics

• Involves 4 anatomical abnormalities

• 3 of them are always present

• 1 of them is acquired

TOF statistics

• Most common cause of blue baby syndrome

• Accounts for 10% of all cyanotic heart defects

TOF is commonly associated with?

Trisomy 21

Nature vs nurture

• Nature: Genetic factors

• Nurture: environmental factors

Blue baby vs pink baby

• Blue baby: cyanotic

• pink baby: acyanotic

4 heart defects of TOF

1. A large VSD

2. Pulmonary Stenosis (RVOT obstruction)

3. Overriding aorta

4. Right Ventricular Hypertrophy (RVH)

Which defect is acquired?

• RVH is acquired

• The other 3 are congenital

TOF anatomical description

Anterior-lateral displacement of the infundibular septum (Conus)

How does the infundibular septum move in TOF?

• It is shifted abnormally towards the front & side of the heart

• Often causing narrowing of the RVOT

TOF Blood Flow

• Low oxygenation d/t mixing of blood in the LV via the VSD

• Mixed blood prefers to go thru the Aorta bc the PA is obstructed

Qp/Qs ratio of TOF

• Qp/Qs DEC’s (more blood systemically)

• Right to Left shunt

  • significantly worsened if there is PA atresia

Stenosis

narrowing or stricture

Atresia

complete or “almost complete” closure

Associated variants of TOF

• TOF w/ pulmonary atresia

• TOF w/ pseudotruncus arteriosus

• Pentalogy of Fallot

• Pink TOF

TOF w/ pulmonary atresia

• Severe variant

• PA forms but is narrowed to a functional or physical close

TOF w/ pseudotruncus arteriosus

• Severe variant

• There is a complete obstruction (atresia) of the RVOT

• D/t an absence of the pulmonary trunk during embryonic development

What is similar in both variants of TOF

• Blood shunts completely from the RV to the LV where it is pumped only thru the aorta

Pentalogy of Fallot

TOF w/ the addition of an ASD

Cyanosis causes

• Reduction in amount of O2 in the blood that flows to the rest of the body

• D/t Narrowing of the Pulm valve & RVOT restricts BF to the lungs

Tet spells

• Sudden episodes of cyanosis during crying or feeding

• BF to the lungs is severely DEC’d

TOF diagnosis

• Often diagnosed in the first few weeks of life

• Prenatal US may show the heart conditions

TOF treatment

• Typically performed the 1st year of life

• Ongoing care is needed after surgery

Tet spells symptoms

• Rapid, deep breathing

• Fainting/loss of consciousness

• INC’ng cyanosis of the lips, tongue, or nail beds

• Irritability or uncontrolled crying

Squatting during a Tet spell

Knee chest position INC’s Aortic wave reflection

How does knee chest position INC aortic wave reflection

• INC’d pressure on left side of heart, DEC’s R to L shunt

• This DEC’s amount of deoxygenated blood entering the systemic circulation

Long term considerations of TOF

• Babies most likely will need additional operations or heart catheterization as they grow older

• Some kids develop leakage from the Pulm valve in the outflow tract which will require a revision

• Higher risk for arrhythmias or valve regurgitation as adults

Overriding Aorta (definition)

• Malalignment defect

• Wedging of the aorta b/w the MV & TV fails to occur bc the OT does not lengthen normally during looping phase

Overriding Aorta anatomically

• Aorta is positioned directly over a VSD instead of over the LV

When would TOF simulate a DORV?

• W/ severe OT obstruction & VSD, aorta overrides ventricular septum & simulates a double outlet RV (DORV) w/ pulmonic stenosis

TOF difference from DORV

TOF has aortic-mitral continuity despite anterior position of aorta & overriding of the RV

Aorta and PA start as a single tube called the

Truncus arteriosus which is divided by the spiral septum

Truncus arteriosus becomes

The aorta

Conus cordis becomes

The Pulmonary artery

What if the spiral septum is not midline but shifted towards the right side of the heart?

• Aorta opening becomes large

• Pulmonary opening becomes small (Pulmonary stenosis)

• Spiral septum would miss the septum

Aortic stenosis is…

• Fatal

• Bc you cannot pump blood out to the body

TOF risk factors

• Alcoholism in the mother

• Diabetes

• Mother > 40 yo

• Malnutrition during pregnancy

• Rubella or other viral illnesses during pregnancy

When does geriatric motherhood begin?

35-40 years old

Classic TOF X-ray

Boot shaped heart

What might be the body’s response to the low saturations & DEC’d pulmonary BF?

• Elevate the Hct

• not uncommon for TOF children to have >50% Hct

• AKA polycythemia

Pink TOF

• Balanced VSD & mild PS

• Results in mostly adequate pulmonary BF

• No cyanosis

Pink TOF symptoms

• Mild symptoms

• May be asymptomatic or develop signs of CHF

• Presentation may be delayed, even into adulthood

Pink TOF Treatment

• Surgery to close the VSD w/ a patch

• Surgery to open the narrowed PA to the lungs

How are the lungs perfused in TOF?

Via extensive collaterals from the systemic arteries

DORV & TOF both have…

↑ incidence of right aortic arch

The spiral septum grows down & attaches to the ventricular septum which:

1. Isolates the ventricles

2. Isolates the aorta & the PA