• Some patients may have left to right shunt will full arterial oxygen saturation.
• PA pressure is normal or low, never is it high.
• All patients have subpulmonic obstruction.
• VSD is non-restrictive usually. So, RVH is in proportion to the LV mass.
• Rarely, VSD is restrictive. Then RVH will be severe due to suprasystemic RV pressure.
• Exercise produces cyanosis due to decrease in systemic vascular resistance leading to increased right to left shunting.
• Hypercyanotic episode is due to acute increase in infundibular obstruction.

Clinical features

• Fetal diagnosis is possible by echo.
• Newborn with severe RVOT obstruction may have only mild cyanosis till ductus closes.
• Hypercyanotic spells or tetralogy spells-
  • More common in patients with iron deficiency anemia.
  • Mechanisms-
    • Acute increase in subpulmonic obstruction due to contraction due to catecholamines or due to hypovolemia.
    • Decreased systemic vascular resistance
• Severe cyanosis.
• Hyperpnea due to hypoxia and metabolic acidosis.
• Can be lethal.
• Murmur intensity is markedly decreased.
• Squatting-
  • Usually after exercise.
  • Instinctive- to increase arterial saturation.
  • Increased systemic vascular resistance decreases shunting.
• Left parasternal impulse is present.
• S2 is single in almost all patients.
• S2 is often loud due to anterior aorta.
• No S3 or S4.
• Wide pulse pressure if
  • PDA
  • AP collaterals or
  • Palliative shunt.
• Mid-systolic murmur
  • Site – inferior to the site of valvular PS murmur
  • Crescendo-decrescendo or plateau shaped
  • Harsh
  • Intensity is inversely proportional to RVOT obstruction
  • Decreases during hypercyanotic spell
  • Absent in TOF with PA
• EDM
  • AR
  • PR
    • In TOF with PA
    • Harsh sawing to and fro murmur
    • Pathognomonic
• AES (aortic ejection sound) – in older patients.
• Continuous murmur-
  • PDA
  • AP collaterals (murmur in back)
• Postoperative-
  • S2 is single (only A2).
  • MSM of PS is often heart due to some degree of residual PS.
  • Low frequency EDM of PR is heart in many.
  • PSM if residual VSD.

Diagnostic studies

• ECG-
  • RVH is evident beyond 3 months when neonatal RVH should have resolved.
  • Right axis deviation is present.
  • In older untreated patients, RV fibrosis may cause ventricular ectopy or arrhythmias.
• Chest X-ray-
  • No cardiomegaly.
  • Upturned apex- boot-shaped heart or coeur en sabot.
  • Concavity of left heart border due to RV infundibular hypoplasia and MPA hypoplasia.
  • Decreased pulmonary vascularity.
  • Right aortic arch in 25%.
• Blood investigations-
  • Hematocrit more than 65% will cause hyperviscosity syndrome.
  • Microcytosis due to iron deficiency can cause cerebrovascular events and should be avoided.
• Echocardiography-
  • With more than 50% override, look for bilateral conus to rule out DORV.
  • TR will not occur despite RV hypertension.
  • In the first few days of life, PS severity is underestimated due to elevated PVR and due to PDA.
  • The VSD is just below the RCC, at 10’O clock position.
• Cardiac catheterization-
  • Stenting for PS has been done along with surgery.
  • AP collaterals can be closed with coils.
  • RV hypertension is equal to LV hypertension.
  • PA anatomy and coronary anatomy clarifications are the usual indications for cath study.
  • PA pressure is normal or low. Elevation suggests diffuse distal pulmonary arterial stenosis.
  • With AP collaterals, calculation of right to left ventricular shunt gives a falsely low value.
  • Pulmonary artery anatomy delineation is especially important in patients who have undergone palliative aortopulmonary shunts.
  • AP collaterals usually originate from the descending aorta. Occasionally they originate from the brachicephalic vessels as in pulmonary atresia.

http://www.heartpearls.com/2009/06/tetralogy-of-fallot-an-article-part-1.html

http://www.heartpearls.com/2009/06/tetralogy-of-fallot-an-article-part-2.html

http://www.heartpearls.com/2009/08/tetralogy-of-fallot-an-article-part-4.html