Tetralogy Of Fallot (TOF)

Tetralogy Of Fallot (TOF), named for French physician Arthur Fallot, is the most common cyanotic congenital heart defect and comprised of four cardiovascular anomalies:

  1. Right ventricular outflow tract (RVOT) obstruction due to pulmonic valve stenosis or hypertrophy of the subpulmonic muscle. This largely determines the extent of physiologic derangements and symptomatology.
  2. RV hypertrophy
  3. Ventricular septal defect (VSD)
  4. Overriding aorta (Ao)

RVOT obstruction reduces blood flow to the lungs resulting in chronic hypoxemia and right-to-left shunting through the VSD. It’s common for these patients to have hemoglobin oxygen saturations in the 70-90% range with extremity cyanosis, failure to thrive, and compensatory polycythemia.

Tet spells” are acute episodes of worsening hypoxemia precipitated by hypovolemia, pain, and anxiety causing near occlusion of the RVOT. If prolonged, the resulting hypoxemia can lead to syncope, worsening cyanosis, or even death. Older patients will instinctively squat to increase systemic vascular resistance (SVR), reducing right-to-left shunting and promoting more blood flow to the lungs to participate in gas exchange. Beta-blockers, volume, and vasoconstrictors can be utilized for inpatients to achieve the same effect.

Surgical correction typically involves closure of the VSD and addressing the RVOT obstruction with resection of redundant muscle, pulmonic valve replacement, etc.

In the parasternal long and short-axis transthoracic echo clips, one can visualize the large VSD and overriding aorta in addition to the significant compensatory RV hypertrophy due to volume and pressure overload from the VSD and RVOT obstruction, respectively.

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