Tetralogy of Fallot

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