Extra Topic 5.1 -- Tetralogy of Fallot

Question 1

What conditions may produce cyanosis in the first year of life?

(A 6-month-old male is scheduled for cardiac catheterization. He has a history of cyanosis since birth, with increasing severity over the past 2 months. The cyanosis seems to worsen with crying and feeding.)

Answer 1

Any condition that results in right-to-left cardiac shunting will produce cyanosis.

The congenital heart defects associated with cyanosis include – tetralogy of Fallot, transposition of the great vessels, truncus arteriosus, tricuspid atresia, and total anomalous return (TAPVR).

Clinical Notes:

• Transposition of the Great Vessels:
  
  • A cyanotic congenital cardiac defect in which there are two parallel circulatory systems, with the right heart pumping deoxygenated blood into the aorta (bypassing the lungs) and the left heart pumping oxygenated blood back into the lungs (the pulmonary artery arises from the left ventricle and the aorta rises from the right ventricle).
  • This defect is incompatible with life unless mixing of oxygenated and deoxygenated blood occurs via an atrial septal defect, a ventricular septal defect, or a patent ductus arteriosus.
• Total Anomalous Pulmonary Venous Return (TAPVR):
  
  • A cyanotic cardiac defect in which all four pulmonary veins make abnormal connections to the systemic circulation (the normal connection would be to the left atrium).
  • The condition is only compatible with life if there is a patent foramen ovale or an atrial septal defect to allow for the passage of systemic and pulmonary venous blood to the left heart.
  • The four variants include:
    
    1. supracardiac (the pulmonary veins drain into the right atrium via the superior vena cava);
    2. infracardiac (the pulmonary veins drain into the right atrium via the inferior vena cava);
    3. cardiac (the pulmonary veins drain into the right heart via a direct connection to the right atrium or via the coronary sinus); and a
    4. mixed variant (the pulmonary veins split up and drain into more than one of the previously noted sites).
• Tricuspid Atresia:
  
  • A cyanotic congenital cardiac defect involving atresia or agenesis of the tricuspid valve.
  • This defect results in an underdeveloped or absent right ventricle.
  • All venous blood return into the right atrium must be shunted into the left atrium through an atrial septal defect.
  • This blood (deoxygenated) then mixes with pulmonary venous return (oxygenated) before entering the left ventricle.
• Truncus Arteriosus:
  
  • A cyanotic congenital cardiovascular defect that results when the truncus arteriosus (an embryological structure) fails to divide into the pulmonary trunk and the aorta, resulting in a single arterial trunk arising from normally formed ventricles by means of a single semilunar valve (truncal valve).

Question 2

What is tetralogy of Fallot (TOF)?

(A 6-month-old male is scheduled for cardiac catheterization. He has a history of cyanosis since birth, with increasing severity over the past 2 months. The cyanosis seems to worsen with crying and feeding.)

Answer 2

Tetralogy of Fallot is the most common cyanotic congenital heart disease, and is composed of four congenital defects:

1. ventricular septal defect (VSD);
2. right ventricular outflow obstruction;
3. overriding aorta; and
4. right ventricular hypertrophy.

• Elevated pressures in the right ventricle from right ventricular outflow obstruction,
• systemic back pressure from the overriding aorta, and
• a large VSD, lead to –
  
  • right ventricular hypertrophy,
  • right-to-left shunting, and
  • hypercyanotic spells (tet spells).

Question 3

What is a hypercyanotic spell?

(A 6-month-old male is scheduled for cardiac catheterization. He has a history of cyanosis since birth, with increasing severity over the past 2 months. The cyanosis seems to worsen with crying and feeding.)

Answer 3

Hypercyanotic spells are –

paroxysmal episodes characterized by increased cyanosis and rate and depth of respirations, potentially leading to loss of consciousness, seizures, cerebrovascular injury, and death.

While the etiology of these spells is not entirely understood,

there are several factors associated with the precipitation of an event, such as – crying, feeding, defecating, fever, exercise, and awakening.

The most likely explanation for the occurrence of these hypercyanotic spells is a sudden increase in right-to-left shunting, secondary to increased right ventricular outflow tract obstruction (i.e. infundibular spasm) and/or decreased systemic vascular resistance.

Question 4

How are hypercyanotic spells managed during anesthesia?

(A 6-month-old male is scheduled for cardiac catheterization. He has a history of cyanosis since birth, with increasing severity over the past 2 months. The cyanosis seems to worsen with crying and feeding.)

Answer 4

Treatment consists of –

• increasing the depth of anesthesia
  
  • (ketamine may be preferred because it maintains or increases systemic vascular resistance),
• hyperventilating with 100% oxygen
  
  • (hypocapnia and hyperoxia decrease PVR),
• administering a fluid bolus,
• increasing SVR with a small dose of phenylephrine or norepinephrine, and
• administering a beta-blocker to decrease infundibular spasm and heart rate.