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Tetralogy of Fallot (TOF)

Clinical Subject Page

Tetralogy of Fallot (TOF)

ICD-10

Q25.0

Specialty

Cardiology

Onset

Chronic

Reviewed

July 2026

On This Page

Overview

-Tetralogy of Fallot (TOF) is characterized by four congenital cardiac defects:
– Right ventricular outflow tract obstruction (RVOTO) due to pulmonary infundibular stenosis
– Right ventricular hypertrophy (RVH)
– Ventricular septal defect (VSD)
– Overriding aorta

Etiology & Risk Factors

  • – Prematurity
    – Maternal exposure during pregnancy:
    – Rubella infection (first trimester)
    – Alcohol consumption
    – Phenytoin use (fetal hydantoin syndrome)
    – Prostaglandin use
    – Respiratory distress syndrome
    – Trisomies (e.g., Down syndrome)

Pathophysiology

  • During fetal development:
    – Anterior and superior deviation of the infundibular septum causes:
  • Malaligned VSD
  • Overriding aorta
  • Right ventricular outflow tract obstruction (RVOT)
  • Blood flow depends on the severity of RVOTO:
  • Large VSD causes equal right and left ventricular pressures.
  • Mild RVOTO → predominantly left-to-right shunt → minimal cyanosis.
  • Severe RVOTO → right-to-left shunt → deoxygenated blood enters systemic circulation.
  • Persistent right-to-left shunting eventually results in right ventricular hypertrophy

Clinical Presentation

  • General
    – Mild Tetralogy of Fallot (TOF) :
    – May be asymptomatic initially.
    – Symptoms of heart failure may develop after 4–6 weeks.
    – Cyanosis:
    – Severity depends on RVOTO.
    – Mild obstruction:
    – Minimal cyanosis (“Pink Tet”).
    – Severe obstruction:
    – Marked cyanosis present from birth.
    Tet Spells (Hypercyanotic Spells)
    – Peak incidence:
    – 2–4 months of age.
    – Triggered by:
    – Crying
    – Feeding
    – Defecation

History Taking

Assess for:
– Cyanosis since birth
– Feeding difficulty
– Failure to thrive
– Dyspnea
– Hypercyanotic (tet) spells
– Episodes triggered by crying or feeding
– Squatting behavior during activity
– Exercise intolerance
– Symptoms of heart failure

Investigations

  • Echocardiography (Confirmatory Test)
    – Prenatal diagnosis is increasingly common with fetal echocardiography.
    – Postnatal echocardiography confirms:
    – Right ventricular outflow tract obstruction
    – Ventricular septal defect
    – Overriding aorta
    – Right ventricular hypertrophy
    – Measures RV outflow tract pressure gradient.
    – Cardiac catheterization may supplement evaluation.
  • Chest X-ray
    – Boot-shaped heart
    – Upturned cardiac apex
    – Right ventricular hypertrophy

Diagnosis

  • Diagnosis is confirmed by:
    – Echocardiography.
    Supportive investigations:
    – Prenatal fetal echocardiography.
    – Chest X-ray.
    – ECG.
    – Pulse oximetry.
    – Hyperoxia test.
    – Cardiac catheterization when required.

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Management

  • 1. Initial Management

    Severe Right Ventricular Outflow Tract Obstruction (RVOTO)

    • Prostaglandin E₁ (PGE₁) infusion to keep the ductus arteriosus patent until definitive surgery.

    2. Management of Acute Tet Spell (Hypercyanotic Spell)

    Initial Measures

    • 100% oxygen
    • Knee-to-chest position (or squatting in older children)
    • Morphine (or alternatives such as fentanyl, midazolam, or ketamine)

    If No Improvement

    • IV sodium bicarbonate (to correct metabolic acidosis)
    • IV fluids (to improve right ventricular filling)
    • Phenylephrine (to increase systemic vascular resistance)
    • IV propranolol (to reduce sympathetic activity and relieve RV outflow tract spasm)

    3. Heart Failure Management

    • Digoxin (inotropic support)
    • Loop diuretics (e.g., furosemide)
    • Avoid ACE inhibitors, as they may decrease systemic vascular resistance and precipitate tet spells.

    4. Definitive Treatment

    Complete Surgical Repair (Preferred)

    Performed within the first year of life, typically before 6 months.

    The procedure includes:

    • Patch closure of the ventricular septal defect (VSD)
    • Relief of the right ventricular outflow tract obstruction (RVOTO) by resecting obstructive infundibular muscle

    5. Palliative Surgery

    If complete repair cannot be performed initially:

    • Blalock–Thomas–Taussig (BT) shunt (most common)
    • Central shunt
    • Other palliative shunts when indicated

    6. Long-Term Follow-Up

    • Regular cardiology follow-up
    • Monitor for:
      • Heart failure
      • Arrhythmias (e.g., ventricular tachycardia)
      • Neurodevelopmental complications

Complications

  • Hypercyanotic (tet) spells
  • Heart failure
  • Cardiac arrhythmias (especially ventricular tachycardia)
  • Neurodevelopmental impairment
  • Chronic hypoxemia if untreated
  • Death if severe disease is not corrected
  •  

Prognosis

  • Without surgery: Approximately 50% of patients do not survive beyond the first 3 years of life.
  • With corrective surgery: >90% of patients survive beyond 25 years of age.
  • Lifelong cardiology follow-up is required to monitor for heart failure and arrhythmias.
  •  

Key Points / Clinical Pearls

  • Tetralogy of Fallot (TOF) is the most common cyanotic congenital heart disease.
  • In Tetralogy of Fallot (TOF) There are 4 defects: Pulmonary stenosis (RVOTO), VSD, Overriding aorta, RVH.
  • Severity of cyanosis depends on the degree of RV outflow tract obstruction.
  • Tet spells are life-threatening and are treated with oxygen, knee-to-chest position, and morphine.
  • Squatting increases systemic vascular resistance (SVR) and decreases the right-to-left shunt, improving oxygenation.
  • Gold-standard diagnostic test: Echocardiography.
  • Definitive treatment: Complete surgical repair in infancy (usually before 6 months of age).
  • Boot-shaped heart on chest X-ray is a classic finding.
  •