Tetralogy of Fallot

Question 1

What is the Tetrad involved in Tetralogy of Fallot?

Answer 1

• Pulmonary Stenosis
• Right Ventricular Hypertrophy - CXR as boot sign (due to the Pulmonary Stenosis)
• Ventricular Septal Defect
• Overriding Aorta - Aorta is displaced to the right (more towards the RV) and dilated over the intraventricular septum due to increased blood flow as it receives blood from both ventricles due to the VSD

Question 2

What are the risk factors in developing TOF?

Answer 2

• Males
• Rubella
• 1st degree history of CHD
• Teratogens: Alcohol, Warfarin, Trimethadione
• Diabetic Mother
• CHARGE syndrome: (Coloboma (a part of the iris is missing - causing vision loss in specific parts of the visual field), Heart Defects, Atresia choanae (narrowing of the nasal cavity - difficulty in breathing), Retardation of growth/development, Genitourinary anomalies, Ear anomalies)
• Di George Syndrome: (22q11 deletion)
• VACTERL association: (Vertebral anomalies, Anorectal malformation, Cardiac defects, Tracheo-oesophageal fistula, Renal anomalies, Limb abnormalities)

Question 3

How is TOF typically identified?

Answer 3

• Picked up on antenatal scans
• Pulmonary Stenosis - murmur = ejection systolic murmur

Question 4

What are the signs and symptoms of TOF?

Answer 4

• Cyanosis (if the Pulmonary Stenosis is so severe that there is Right to Left shunting due to the increased pressure)
• Clubbing
• Poor feeding
• Poor weight gain
• Ejection Systolic Murmur in the Pulmonary Area

Question 5

What are the features of the mild form of TOF?:

Answer 5

• These infants have mild PS/RVH and are usually asymptomatic as there is a left to right shunt = acyanotic
• However, the disease tends to progress and by the age 1-3 the child will develop cyanosis

Question 6

What are the features of the moderate form of TOF?:

Answer 6

• Infants tend to present within the first few weeks of life with cyanosis and respiratory distress
• These patients are prone to develop recurrent chest infections/ failure to thrive

Question 7

What are the features of extreme form of TOF?:

Answer 7

• These infants will have pulmonary atresia or absent pulmonary valves
• True duct dependant lesions
• only way deoxygenated blood can flow into the lungs is through the patent ductus arteriosus
• These infants are detected on antenatal scans
• They will present within the first few hours of life with marked respiratory distress and cyanosis

Question 8

What is the definition of Hypoxic “tets” Spells?

Answer 8

• Tet Spells are intermittent periods where the right to left shunt becomes worse causing a cyanotic episode
• These episodes are worsened by waking, physical exertion and crying

Question 9

What are the Hypoxic Spells?

Answer 9

• 1. Paroxysm of hyperpnoea: Rapid, deep respirations due to increased Right to Left Shunting, therefore there is an increase in CO2 which stimulates the central respiratory centre. This worsens the Right to Left shunting causing worse hypoxia
     -2. Irritability: prolonged, unsettled crying
     -3. Increasing Cyanosis

Question 10

What is the peak age for Tets Spells?

Answer 10

• 2/4 months

Question 11

What is the Treatment for Hypoxic “tets” Spells?

Answer 11

• Squatting/ Knees to the chest
• Give Oxygen
• Beta- Blockers: relaxing the RV and therefore improving flow to the pulmonary vessels
• IV fluids (Increasing preload and therefore the volume of blood going to the pulmonary vessels)
• Morphine (decreases Respiratory Drive)
• Sodium Bicarbonate (used to buffer a metabolic acidosis)
• Phenylephrine Infusion (used to increase systemic vascular resistance - increasing pulmonary perfusion)

Question 12

What do you see on examination in TOF?

Answer 12

• General: Central Cyanosis, Clubbing
• Palpation: Thrill, Heave
• Auscultation: Loud, single S2 sound (due to the closure of the aortic valve in diastole), Pansystolic Murmur (best auscultated mid/upper left sternal edge), Ejection click (high pitch noise which occurs at the maximal opening of the semilunar valves), continuous-machinery murmur
• Signs of Congestive Heart Failure: Sweating, Pallor, Tachycardia, Generalised Oedema, Bilateral Bibasal Crackles, gallop Rhythm

Question 13

What is the other Differential Diagnosis for Tetralogy of Fallot?

Answer 13

• 1. Other Cyanotic CHD: Critical PS, Transposition of Great Arteries, Totally Anomalous Pulmonary Venous Drainage
     -2. Isolated VSD: commonest CHD, does not cause cyanosis as the shunt is left to right unless Eisenmenger syndrome develops
     -3. Sepsis: should be suspected with any infant with respiratory distress and hypoxia

Question 14

What investigations are required for Tetralogy of Fallot?

Answer 14

• ECG: Shows signs of RVH and Right Axis Deviation
• Microarray: if genetic syndromes suspected
• CXR: may show a boot shaped heart due to the RVH and reduced pulmonary vascular marking
• ECHO: gold standard for conformation of diagnosis
  -Cardiac CT angiogram
  -Cardiac MRI

Question 15

What is the Medical Management of Tetralogy of Fallot?

Answer 15

Medical - 1. Squatting - children squat/ keep their knees to their chest, this increases venous return and therefore increase systemic resistance
2. Prostaglandin Infusion - this helps maintain PDA in the more severe forms. PGE1 (alprostadil) or PGE2 (dinoprostone). Side effects: apnoeas, bradycardia and hypotension
3. Beta- Blockers: Propranolol - reduces the heart rate and thus the venous return
4. Morphine: Reduces Respiratory Drive and therefore hyperpnoea

Question 16

What is the Surgical Managment of Tetralogy of Fallot?

Answer 16

• Total Surgical Repair by open heart surgery