Pathophysiology

  • 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

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