A 10-day-old boy born at home is brought to the emergency department due to difficulty breathing and sweating with feeds. He was born at 38 weeks gestation via spontaneous vaginal delivery. The patient has been breastfeeding every 2 hours for 5-10 minutes per side. The mother notes that he sweats and his lips turn blue while he feeds. Weight is at the 5th percentile and length is at the 50th percentile. On examination, the patient is currently not cyanotic. There is a III/VI systolic crescendo-decrescendo murmur best heard along the left upper sternal border. Chest x-ray is shown below:
Show Explanatory Sources
Which of the following pressure changes most likely occur in this patient during feedings?
Tetralogy of Fallot | |
Pathophysiology |
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Clinical presentation |
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Clinical findings |
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LUSB = left upper sternal border; RVH = right ventricular hypertrophy; RVOT = right ventricular outflow tract. | |
This neonate has diaphoresis and episodic cyanosis with feeding, suggesting cyanotic congenital heart disease. The murmur of right ventricular outflow tract (RVOT) obstruction (ie, pulmonic stenosis) and evidence of right ventricular hypertrophy (ie, boot-shaped heart) on chest x-ray are consistent with tetralogy of Fallot (ToF). The anatomic defects of ToF are RVOT obstruction with an overriding aorta and large ventricular septal defect (VSD); concentric right ventricular hypertrophy develops due to increased right ventricular pressure load compared to normal.
The degree of RVOT obstruction is the major driver of symptoms in ToF because it determines how much blood flows through the pulmonary artery to the lungs and the magnitude and direction of shunting through the VSD. Because some degree of RVOT obstruction is fixed and some degree is dynamic (ie, subject to an increase with activity [eg, crying, feeding]), many patients have left-to-right or neutral shunting through the VSD at baseline (and are acyanotic) but develop cyanosis when a dynamic increase in RVOT obstruction causes right-to-left shunting through the VSD (ie, tet episode).
During a tet episode, increased RVOT obstruction leads to increased right ventricular pressure and facilitates right-to-left shunting. There is also decreased pulmonary arterial pressure (blood cannot pass through the RVOT tract into the pulmonary artery, reducing pulmonary blood flow), and decreased left atrial pressure (the left atrium receives less blood returning from the lungs). Due to the large size of the VSD in ToF, left ventricular pressure usually closely matches right ventricular pressure (ie, the ventricles are somewhat like a single chamber).
A tet episode may be improved by bringing the knees to the chest. This maneuver increases systemic afterload, reducing right-to-left shunting through the VSD and forcing more blood through the RVOT.
Educational objective:
The major defects in tetralogy of Fallot are right ventricular outflow tract (RVOT) obstruction and a ventricular septal defect (VSD). In many patients, activities (eg, feeding, crying) can precipitate cyanotic episodes (tet episodes) by causing a dynamic increase in RVOT obstruction. During these episodes, increased right ventricular pressure results in right-to-left shunting through the VSD; because blood is shunted away from the pulmonary circulation, pulmonary arterial and left atrial pressures are decreased.