the most common cyanotic congenital heart defect
Tetralogy of Fallot
representing about 10% of all congenital heart defects
What TETRALOGY OF FALLOT ?
the simultaneous occurrence of the following four defects:
1-ventricular septal defect (VSD)
2-pulmonary stenosis
3-overriding aorta
4-right ventricular hypertrophy
Other cardiac defects associated with TOF?
These occur in ∼ 40% of patients.
Atrial septal defect (ASD)
PDA
Anomalous coronary arteries
most commonly a left anterior descendingcoronary artery arising from the right coronary artery and crossing the anterior surface of the right ventricular outflow tract
Dual coronary supply
Describe the four structuresa abnormalities in TOF ?
1- Right ventricular outflow tract obstruction (RVOTO) due to pulmonary infundibular stenosis and can be valvular , supra valvular
2-Right ventricular hypertrophy (RVH) Continued right-to-left shunting results in RVH.
3- Ventricular septal defect (VSD) : Large
4- Overriding aorta (the aorta is displaced above the VSD) and receives from right and left ventricle
Etiology of TOF ?
1- Typically sporadic
2- Associated with the following genetic disorders:
DiGeorge syndrome [18][19]
Down syndrome [20][21]
3 Maternal exposures during pregnancy
Alcohol consumption
Phenylketonuria [22][23]
Diabetes
Physiologic blood flow in TOF is determined by
the severity of PS
1- A large VSD → equal pressures in the right and left ventricles → blood flow along the path of least resistance
2-When Pulmonary Resistance Is Lower → Left-to-Right Shunt (Acyanotic Phase)
If resistance through the RVOT to the lungs is lower than resistance in the systemic circulation, blood will flow:
• From the left ventricle → right ventricle → pulmonary circulation.
This results in:
• Left-to-right shunt
• Adequate oxygenation
• The patient remains acyanotic (no cyanosis).
- When RVOT Obstruction Increases → Right-to-Left Shunt (Cyanotic Phase)
If RVOT obstruction becomes severe, resistance to pulmonary blood flow increases.
Now the easier path for blood is through the VSD into the left ventricle and then into the aorta.
Blood flow becomes:
• Right ventricle → left ventricle → aorta
This causes:
• Right-to-left shunt
• Deoxygenated blood entering systemic circulation
• Cyanosis.
Dynamic Nature of RVOT Obstruction
A key feature of TOF is that RVOT obstruction can fluctuate.
A patient who normally has mild or minimal cyanosis can suddenly develop increased obstruction, leading to:
• Increased right-to-left shunting
• Sudden worsening cyanosis.
Hypercyanotic Spells (Tet Spells) and it Pathophysiology
In severe cases, the RVOT can almost completely obstruct, causing:
• Profound cyanosis
• Sudden hypoxic episodes known as Tet spells (hypercyanotic spells).
The exact cause is not fully understood, but several mechanisms are suggested:
• Increased infundibular contractility (spasm of the RV outflow tract)
• Peripheral vasodilation → decreases systemic vascular resistance
• Hyperventilation
• Stimulation of right ventricular mechanoreceptors
Clinical features of TOF ? In general
SYMPTOMS
1- cyanosis
2- blue clubbing due to hypoxia ( 6 months - 1 year to appear )
3-failure to thrive
4- Hypoxic (Tet) spells
SIGN
1- murmurs
2- single S2 right ventricular impulse at the left sternal border are typical findings.
unrepaired tetralogy of Fallot are at increased risk for cerebral thrombo-embolism and cerebral abscesses resulting, in part, from their right-to-left intracardiac shunt
Sign and symptoms of heart failure
Cyanosis in TOF characteristic
1-Infants initially may be acyanotic
Newborns may appear well initially due to adequate pulmonary blood flow via the patent ductus arteriosus.
At birth, the ductus arteriosus is normally patent, allowing blood to flow from the aorta to the pulmonary artery, which ensures adequate pulmonary blood flow.
• Cyanosis develops gradually as the ductus closes and infundibular obstruction increases.
2- Mild obstruction → more pronounced left-to-right shunt via VSD → little or mild cyanosis
Called pink tets or pink falot
3- Severe obstruction → more pronounced right-to-left shunt via VSD → severe cyanosis
Hypoxic (Tet) spells [symptom]
Tet spells: intermittent hypercyanotic, hypoxic episodes with a peak incidence at 2–4 months after birth
1- During a spell, the child typically becomes restless and agitated and may cry inconsolably.
2- An ambulatory toddler may squat.
squatting → ↑ SVR → ↓ right-to-left shunt → ↑ blood flow to pulmonary circulation → ↓ hypoxemia → relief of symptoms
3- Hyperpnea occurs with gradually increasing cyanosis and loss of the murmur.
4- In severe spells, prolonged unconsciousness and convulsions, hemiparesis, or death may occur.
5- Associated with psychological and physical stress (e.g., crying, feeding, defecation)
Murmur and other auscultatory findings in TOF
1- pulmonary stenosis murmur is the usual initial abnormal finding
2-With increasing severity of pulmonary stenosis, the murmur becomes shorter and softer
Due to the amount of flow across the right ventricular outflow tract will decrease as the obstruction increases, due to the shunting of blood right-to-left across the VSD
3- Harsh systolic ejection crescendo-decrescendo murmur at the left upper sternal border Caused by RVOTO, not the associated VSD
4- In patients with TOF, the auscultated murmur is determined by the amount of blood flow across the RVOTO. Therefore, during tet spells, the murmur may disappear.
5- murmur appreciated best along the left mid to upper sternal border with radiation posteriorly
6- single S2 “”pulmonic component is rarely audible””. and right ventricular impulse at the left sternal border are typical findings. Possible RV heave and systolic thrill
TOF and chest infection?
Because the lung is dry , there is no chest infections
But if there is a chest infection suspecte TB
Diagnostics in TOF : Prenatal diagnosis
Most cases are now diagnosed before birth due to improvements in fetal echocardiography
Diagnostics in TOF : Imaging and finding , the confirmatory and main diagnostic tool
1- Echocardiography (confirmatory test)
Two-dimensional echocardiography with Doppler is the primary investigation for diagnosing TOF and for preoperative assessment.
In many cases, transthoracic echocardiography (TTE) provides sufficient information, while transesophageal echocardiography (TEE) is used when additional clarification is required.
Detection of the main features of TOF
• Location and number of ventricular septal defects (VSD) • Anatomy and severity of right ventricular outflow tract obstruction (RVOTO) • Coronary artery and aortic arch anatomy • Presence of associated cardiac anomalies
Quantification of right ventricular outflow tract pressure gradient
Supplementary cardiac catheterization may be performed.
Diagnostics in TOF : ECG findings
Right axis deviation
Prominent anterior R waves (V1–V2) anterior leads
Prominent posterior S waves
Right atrial enlargement and RVH (P pulmonale)
Diagnostics in TOF : Pulse oximetry
↓ SpO2
Diagnostics in TOF : Hyperoxia test
helps to distinguish cardiac from pulmonary causes of cyanosis
In this test, PaO2 is measured during the administration of 100% oxygen. When cyanosis results from a right-to-left-shunt, the continued mixing of oxygenated with low-oxygenated blood results in continued hypoxemia and low PaO2, despite optimum oxygen supply.
Tetralogy of Fallot (TOF): Diagnostic Evaluation image rather than echo ?
2-Chest x-ray
Boot-shaped heart (due to upturned cardiac apex and RVH and due to small main pulmonary artery)
Normal or decreased pulmonary vascular markings
Concave pulmonary artery segment
Right-sided aortic arch in ~25% of patients
Cardiac Catheterization in TOF
Although echocardiography often provides sufficient information, cardiac catheterization may still be required to evaluate:
• RV outflow tract obstruction levels
• Pulmonary artery stenosis or hypoplasia
• Coronary artery anatomy
• Aortopulmonary collateral vessels
• Additional VSDs
Hemodynamic findings
• Equal left and right ventricular systolic pressures
• Normal or low pulmonary artery pressure
• Oxygen saturation reflecting degree of right-to-left shunting
Angiography helps visualize:
• RV outflow obstruction
• Pulmonary artery branches
• Coronary arteries
• VSD anatomy
Labs in TOF ?
1- CBC : polycythemia or microcytic hypochromic anemia
2- ABG : acidosis due to hypoxia ——> increase lactic acid
What is the treatment used to maintain ductus arteriosus patency in certain congenital heart diseases?
Prostaglandin E1 (PGE1) infusion, commonly given as IV alprostadil.
What is the starting dose of IV alprostadil?
0.05–0.1 μg/kg/minute IV infusion, titrated as needed under specialist guidance.
What is the mechanism of action of Prostaglandin E1?
It prevents closure of the ductus arteriosus, creating an intentional shunt that allows mixing of oxygenated and deoxygenated blood, improving systemic oxygenation.
