Learning objectives

• Define tetralogy of Fallot
• Describe the signs and symptoms of tetralogy of Fallot
• Understand the pathophysiology of tetralogy of Fallot
• Anesthetic management of a patient with tetralogy of Fallot

Definition and mechanisms

• Tetralogy of Fallot (TOF) is one of the most congenital heart defects (10%), resulting in a right-to-left shunt characterized by
  • Large non-restrictive ventricular septal defect (VSD)
  • Valvular, subvalvular, or supravalvular pulmonary stenosis, causing right ventricular outflow tract obstruction (RVOTO)
  • Right ventricular hypertrophy
  • Overriding aorta
• Cyanotic heart disease
• TOF often presents with low birth weight and prematurity
• TOF may present with other anatomical anomalies 
  • Stenosis of the left pulmonary artery (40%)
  • Bicuspid pulmonary valve (60%)
  • Right-sided aortic arch (25%)
  • Coronary artery anomalies (10%)
  • Patent foramen ovale or atrial septal defect → pentalogy of Fallot
  • Atrioventricular septal defect
  • Partially or totally anomalous pulmonary venous return

Signs and symptoms

• Right-to-left shunt
• Cyanosis (bluish coloration of the skin caused by hypoxemia)
• Hypoxia/low SpO2 (60-90%) with little or no response to oxygen therapy
• Shortness of breath and rapid breathing, especially during feeding or exercise
• Heart murmurs (pansystolic and ejection systolic)
• Abnormal, rounded shape of the nail bed in the fingers and toes (clubbing)
• Poor weight gain
• Tiring easily during feeding or exercise
• Irritability
• Prolonged crying
• Polycythemia
• Baby may turn blue with breastfeeding or crying

Tet spells

• Infants and children with unrepaired TOF may develop tet spells → acute hypoxia spells, characterized by shortness of breath, cyanosis, agitation, and loss of consciousness (syncope)
• Initiated by any event (i.e., crying, bowel movements, anxiety, pain, dehydration, or fever) that leads to decreased oxygen saturation or that causes decreased systemic vascular resistance (SVR) → increased shunting through the VSD (increased right-to-left shunt)
• Decrease in frequency after the first four years of life
• Older children will squat to increase the SVR → temporary reversal of shunt

Complications

• Endocarditis
• Arrhythmias (particularly supraventricular or ventricular)
• Pulmonary regurgitation
• Dizziness, fainting, or seizures due to hypoxemia
• Delayed growth and development

Risk factors

• Viral illness during pregnancy (rubella)
• Maternal alcohol consumption
• Maternal smoking
• Maternal diabetes mellitus or gestational diabetes
• Maternal age >40
• Family history of TOF
• Down syndrome or DiGeorge syndrome
• Tracheoesophageal fistula or VACTERL association 
• Male gender

Pathophysiology

Anatomy of TOF allows mixing of blood between the pulmonary and systemic circulations (usually at VSD) → right-to-left shunt adding deoxygenated blood to the systemic circulation → cyanosis

Diagnosis

• Many patients are diagnosed prenatally 
• Chest radiography: Abnormal “coeur-en-sabot” (boot-like) appearance of the heart 
• Electrocardiogram: Right ventricular hypertrophy along (tall R-waves in lead V1 and deep S-waves in lead V5-V6) with right-axis deviation 
• Echocardiogram: Presence of VSD, right ventricular hypertrophy, and aortic override; color Doppler to measure the degree of pulmonary stenosis

Treatment

• Surgical repair
  • Patch closure of the VSD to separate the pulmonary and systemic circulation
  • Enlargement of the RVOT (increase the size of the pulmonary valve and pulmonary arteries) to relieve RVOTO
• Usually takes place in the first year following birth, at age 3-6 months
• Intraoperative transesophageal echo to evaluate the VSD closure and RVOT

Long-term complications after TOF surgery

• Chronic pulmonary valve regurgitation
• Tricuspid valve regurgitation
• VSD that may continue to leak after repair or may need re-repair
• Hypertrophic right or left ventricle and dysfunction
• Arrhythmias
• Coronary artery disease
• Aortic root and valve dilation
• Sudden cardiac death

Management

Management of tet spells during anesthesia

• Goal: Increase oxygenation, improve cardiac output, and reduce infundibular spasm and right-to-left shunt
• Give 100% oxygen and check the endotracheal tube position
• Deepen anesthesia and give an opiate bolus (e.g., 0.1 mg/kg morphine)
• Fluid bolus
• Vasopressor therapy (e.g., 5 mcg/kg phenylephrine)
• β-blockers (e.g., 0.1-0.3 mg/kg propranolol)
• Knee-to-chest flexion position

Keep in mind

• TOF is characterized by the presence of a VSD, RVOTO, right ventricular hypertrophy, and overriding aorta
• TOF is one of the most common cyanotic heart defects
• Prevention of tet spells is the key for safe anesthesia

Suggested reading

• Wilson R, Ross O, Griksaitis MJ. Tetralogy of Fallot. BJA Educ. 2019;19(11):362-369.
• Pollard BJ, Kitchen G. Handbook of Clinical Anaesthesia. 4th ed. Taylor & Francis group; 2018. Chapter 2 Cardiovascular system, Tully RP and Turner R.