Tetralogy of Fallot (TOF)

1. Tetralogy of Fallot
(TOF)
Dr. Sayeedur Rahman Khan Rumi
dr.rumibd@gmail.com
MD Final Part Student
NHFH&RI

2. Introduction
• It is the most common form of cyanotic heart
disease .
• It occurs in approximately 1 in 3000 live births and
accounts for 10% of CHD.
• It is also the most common CHD requiring surgical
correction in the first year of life without which
only 10% of patient survive beyond the age of 20
yrs.

3. French physician Étienne-
Louis-Arthur Fallot, who first
described TOF in the late
19th century.
Arthur Fallot

4. Development of TOF
A. During the fifth week, pairs
of opposing ridges appear
in the truncus (right
superior truncus swelling &
left inferior truncus
swelling).
B. Hence, while growing
toward the aortic sac, the
swellings twist around each
other, foreshadowing the
spiral course of the future
septum.
C. After complete fusion, the
ridges form the
aorticopulmonary septum,
dividing the truncus into an
aortic and a pulmonary
channel.

5. Development of TOF
• TOF, is due to an unequal
division of the conus
resulting from anterior
displacement of the
conotruncal septum.

6. Pathology
• The original description of
TOF included the following
four abnormalities:
1. A large VSD
2. RVOT obstruction
3. RVH, and
4. Overriding of the aorta.

7. Pathology
• In actuality, only two abnormalities are required, a VSD large
enough to equalize pressures in both ventricles and an RVOT
obstruction.
• The RVH is secondary to the RVOT obstruction, and the
overriding of the aorta varies.
• The VSD in TOF is a large perimembranous defect with
extension into the subpulmonary region.
• The RVOT obstruction is most frequently in the form of
infundibular stenosis (45%).
• The obstruction is rarely at the pulmonary valve level (10%).
• A combination of the two may also occur (30%).
• The pulmonary valve is atretic in the most severe form of
the anomaly (15%)

8. Abnormal Physiology
• Because the VSD is large, with an area about as great as that
of the aortic valve, both ventricles and the aorta have
essentially the same systolic pressures.
• The most important hemodynamic factor is the ratio
between the resistance to flow into the aorta and the
resistance to flow across the right ventricular infundibulum.
• If the stenosis is not severe and resistance to right
ventricular outflow is not large, the pulmonary flow may be
more than twice the systemic flow, and the arterial oxygen
saturation may be normal (acyanotic tetralogy of Fallot).
• However, the resistance to the pulmonary flow may be
increased markedly, causing right-to-left shunting, arterial
desaturation, and subsequent polycythemia.

9. • The drugs, heart rate, or maneuvers that increase
myocardial contractility or decrease right ventricular
volume increase infundibular obstruction, often
partially dynamic.
• In addition, the infundibular hypertrophy may increase
gradually over time.
• As the systolic pressure in the right ventricle cannot
exceed that in the left ventricle because of the large
VSD, the right ventricle is “protected” from excessive
pressure and work, and so heart failure is uncommon.

10. Associated defects
• Right aortic arch ( 30%)
• Anomalous origin of LAD from RCA (10%)
• ASD secundum (15%) : pentalogy of Fallot
• Persistent left SVC (10%)

11. Natural History
• Infants with acyanotic TOF gradually become cyanotic.
• Patients who are already cyanotic become more cyanotic as the
infundibular stenosis worsens and polycythemia develops.
• Polycythemia develops secondary to cyanosis.
• Development of relative iron-deficiency states (i.e., hypochromia).
• Hypoxic spells may develop in infants.
• Growth retardation may be present if cyanosis is severe.
• Brain abscess and cerebrovascular accident rarely occur.
• Subacute bacterial endocarditis (SBE) is occasionally a
complication.
• Some patients, particularly those with severe TOF, develop aortic
regurgitation (AR).
• Coagulopathy is a late complication of a long-standing cyanosis.

12. Clinical
Manifestations

13. History
• Most patients are symptomatic with cyanosis at birth
or shortly thereafter.
• Dyspnea on exertion, squatting, or hypoxic spells
develop later even in mildly cyanotic infants.
• Occasional infants with acyanotic TOF may be
asymptomatic or may show signs of CHF from a large
left-to-right ventricular shunt.

14. Physical Examination
• Growth is usually normal
unless cyanosis is
extreme.
• Clubbing of the fingers
and toes occurs after 3
months of age and is
proportional to the level
of cyanosis.
• Varying degrees of
cyanosis, tachypnea, and
clubbing (in older infants
and children) are present.

15. • Increased right ventricular activity is observed.
• A systolic thrill may be palpable at the left midsternal
border, with a harsh midsystolic murmur in that
location.
• The shorter the murmur, the more severe the
infundibular pulmonary stenosis.
• The first heart sound (S1) is usually normal
• Second heart sound is characteristically single, because
the pulmonary component is too soft to be heard.
• A continuous murmur is heard if a PDA or large
collateral vessels are present.
• An early systolic ejection sound at the left sternal
border and apex is uncommon; its presence suggests
primarily valvular pulmonary stenosis.

16. Cardiac findings in cyanotic tetralogy of Fallot.
A long ejection systolic murmur at the upper and mid left sternal
border and a loud, single S2 are characteristic auscultatory findings of
TOF.

17. Investigation

18. Hematologic and Other Laboratory
Studies
• Hemoglobin and
hematocrit
• Platelet counts and
clotting studies
• Serum uric acid levels
To evaluate -
Iron deficiency
anemia,
Polycythemia &
Hyperuricemia

19. Electrocardiography
• RAD
• There is right ventricular hypertrophy, with a tall R wave in the
right precordial leads and a deep S wave in the left leads.
• A QRS duration of >180 ms is a predictor of sustained VT and
sudden cardiac death.
• Some of these patients have right atrial hypertrophy.

20. Chest X-ray
• The total heart size is usually normal on chest xray,
but right ventricular enlargement is present in the
lateral view.
• The pulmonary segment is concave and the apex is
elevated, giving the coeur en sabot (boot-shaped)
contour.
• The aorta arches to the right in many cases.
• Pulmonary flow is diminished.

22. Echocardiography
• Two-dimensional echocardiography and Doppler
studies usually make the diagnosis and quantitate the
severity of TOF.
• A large, perimembranous infundibular VSD and
overriding of the aorta are readily imaged in the
parasternal long-axis view.
• Anatomy of the RVOT, the pulmonary valve, the
pulmonary annulus, and the main PA and its branches
is imaged in the parasternal short-axis and subcostal
short-axis views.

23. • Doppler studies estimate the pressure gradient across
the RVOT obstruction.
• Anomalous coronary artery distribution can be
imaged accurately by echocardiographic studies.
• The major concern is to rule out any branch of the
coronary artery crossing the RVOT.
• Associated anomalies such as ASD and persistence of
the left superior vena cava (LSVC) can be imaged.

24. • PLAX view showing the overriding aorta and a large
subaortic VSD (star).
• RVH is also present

25. Color flow imageing showing VSD jet

26. PLAX view of repaired TOF showing RV is dilated and the
echogenic region at the superior portion of the IVS
represents synthetic patch (arrow)

27. Cardiac Catheterization
• To assess the anatomy of RVOT and main PA
branches, RV and LV function, site and size of VSD
and competence of aortic valve.
• Arterial O2 saturation is <85%
• Identical systolic pressure in RV and LV and low
systolic pressure in PA (diagnostic of TOF)

28. RV graphy
• Percentage of
overriding aorta
• Size of the VSD
• RVOT obstruction
• To differentiate
TOF from DORV

29. LV graphy

30. Root & Arch aortography

31. Hypoxic Spell

32. Hypoxic Spell
• Also called cyanotic spells, hypercyanotic spells, “tet”
spells
• Hypoxic spells are characterized by:
Paroxysm of hyperpnea (i.e., rapid and deep respiration),
Irritability and prolonged crying,
Increasing cyanosis, and
Decreasing intensity of the heart murmur.
• Hypoxic spells occur in infants, with a peak incidence
between 2 and 4 months of age.
• These spells usually occur in the morning after crying,
feeding, or defecation.
• A severe spell may lead to limpness, convulsion,
cerebrovascular accident, or even death.

34. Mechanism of hypoxic spell
• Hypercyanotic episodes (spells) in patients with
tetralogy are of uncertain origin.
• It is likely that some episodes are caused by unusual
hyperactivity of muscular fibers in the right ventricular
outflow tract that produce or exaggerate the
infundibular stenosis, increasing pulmonary resistance
and thus increasing the right-to-left shunting.
• Some spells may be caused by a decrease in peripheral
resistance and systemic arterial pressure, which also
may cause the right-to-left shunt to increase and
pulmonary blood flow to decrease.

35. A vicious circle of hypoxic spell.
• A decrease in the arterial PO2 stimulates the respiratory center, and
hyperventilation results.
• Hyperpnea increases systemic venous return.
• In the presence of a fixed right ventricular outflow tract (RVOT), the
increased systemic venous return results in increased right-to-left (R-L)
shunt, worsening cyanosis.

36. Treatment of Hypoxic spell
Treatment of hypoxic spells is aimed at breaking this circle
by using one or more of the following maneuvers:
• The infant should be picked up and held in a knee–chest
position.
• Oxygen: high flow high conc.
• Morphine sulfate, 0.2 mg/kg administered
subcutaneously or intramuscularly, suppresses the
respiratory center and abolishes hyperpnea (and thus
breaks the vicious cycle).
• Acidosis should be treated with sodium bicarbonate
(NaHCO3), 1 mEq/kg administered IV. NaHCO3 reduces
the respiratory center–stimulating effect of acidosis.

37. • Propranolol, 0.01 to 0.25 mg/kg (average, 0.05 mg/kg)
administered by slow IV push, reduces the heart rate
and may reverse the spell.
If the hypoxic spells do not fully respond to these
measures, the following medications can be tried:
• Ketamine, 1 to 3 mg/kg (average, 2 mg/kg)
administered IV over 60 seconds.
• It increases the systemic vascular resistance (SVR) and
sedates the infant.
• Vasoconstrictors like Phenalepherine 0.02mg/kg I/V.
• General Anesthesia (rarely required)

38. Management

39. Medical
• Hypoxic spells should be recognized and treated
promptly.
• It is important to educate parents to recognize the spells
and know what to do.
• Oral propranolol therapy, 0.5 to 1.5 mg/kg every 6 hours,
is occasionally used to prevent hypoxic spells while
waiting for an optimal time for corrective.
• Relative iron-deficiency states should be detected and
treated.
• Iron-deficient children are more susceptible to
cerebrovascular complications.

40. Surgical

41. Palliative Shunt Procedures
Shunt procedures are performed to increase Pulmonary
Blood Flow.
Indication:
1. Neonates with TOF and pulmonary atresia
2. Infants with hypoplastic pulmonary annulus
3. Children with hypoplastic PAs
4. Unfavorable coronary artery anatomy
5. Infants younger than 3 to 4 months old who have
medically unmanageable hypoxic spells
6. Infants weighing less than 2.5 kg

42. Palliative Shunt Procedures
• Classic BT shunt, anastomosed between the subclavian
artery and the ipsilateral PA, is usually performed for
infants older than 3 months because the shunt is often
thrombosed in young infants.
• With a modified BT shunt, a Gore-Tex interposition
shunt is placed between the subclavian artery and the
ipsilateral PA.
• This is the most popular procedure for any age,
especially for infants younger than 3 months of age.
• The surgical mortality rate is 1% or less.

43. Classic Blalock Taussig
Shunt
Modified Blalock Taussig
Shunt

44. • The Waterston shunt, anastomosed between the
ascending aorta and the right PA, is no longer
performed because of a high incidence of surgical
complications.
• The Potts operation, anastomosed between the
descending aorta and the left PA, is no longer
performed either.
• It may result in heart failure or pulmonary
hypertension, as in the Waterston operation.

46. Complete Repair Surgery
• Total repair of the defect is carried out under
cardiopulmonary bypass, circulatory arrest, and
hypothermia.
• The procedure includes patch closure of the VSD,
widening of the RVOT by division or resection of the
infundibular tissue; and pulmonary valvotomy.
Mortality:
• For patients with uncomplicated TOF, the mortality rate
is 2% to 3% during the first 2 years.
• Patients at risk are those younger than 3 months and
older than 4 years, as well as those with severe
hypoplasia of the pulmonary annulus and trunk.

47. Diagrammatic representation of surgical repair of tetralogy of Fallot.
1. Patch closure of a VSD
2. Right ventricular outflow/main pulmonary artery outflow patch
(transannular patch)

48. Complications
• Bleeding problems may occur during the postoperative
period, especially in older polycythemic patients.
• Pulmonary valve regurgitation may occur, but mild
regurgitation is well tolerated.
• Right bundle branch block (RBBB) on the ECG caused
by right ventriculotomy, which occurs in more than
90% of patients, is well tolerated.
• Complete heart block (i.e., <1%) and ventricular
arrhythmia are both rare

49. Thank you