Congenital Heart Defects and Tet Spells

Pediatrics · Cardiac. Congenital Defects·Updated 2026-10-28

What it is

Blood flows from higher to lower pressure, so congenital heart defects are classified by their effect on blood flow. Defects with increased pulmonary blood flow (ventricular septal defect, atrial septal defect, patent ductus arteriosus) shunt blood left to right, flood the lungs and cause heart failure without cyanosis. Defects with decreased pulmonary blood flow, such as tetralogy of Fallot (VSD, pulmonary stenosis, overriding aorta, right ventricular hypertrophy), shunt unoxygenated blood right to left and cause cyanosis. Obstructive defects (coarctation of the aorta, aortic and pulmonic stenosis) raise pressure behind the narrowing.

What the NCLEX focuses on

Large VSD: tachypnea, sweating and tiring during feedings, poor weight gain, frequent respiratory infections and a loud holosystolic murmur, without cyanosis or clubbing.
Tet spell: crying, feeding, defecation or a painful procedure triggers hyperpnea, deepening cyanosis and irritability that progresses to limpness or loss of consciousness.
Chronic hypoxemia produces clubbing and polycythemia; dehydration thickens the blood further and raises the risk of stroke.
Coarctation: higher blood pressure in the arms than the legs, bounding brachial pulses, weak or absent femoral pulses and cool feet.
PDA: continuous machine-like murmur and bounding pulses; indomethacin or ibuprofen closes it in preterm infants, while prostaglandin E1 keeps it open in duct-dependent defects.
Digoxin: count the apical pulse for 1 full minute before every dose and hold it for bradycardia per the prescription; vomiting and bradycardia are toxicity signs.

Priority nursing actions

Place the infant in the knee-chest position (an older child squats), which raises systemic vascular resistance and sends more blood to the lungs, and calm the child.
Give 100% oxygen by face mask.
Give the prescribed morphine (IV, subcutaneous or IM) to slow breathing and relax the right ventricular outflow tract.
Give the prescribed IV fluid bolus, and propranolol or phenylephrine if the spell continues.
Monitor SpO2, heart rate and level of consciousness, report the spell and prepare the family for surgical repair.

Numbers to know

Value	Normal or target	Why it matters
Digoxin hold (per prescription)	Infant apical pulse below 90 to 110/min; older child below 70/min	Bradycardia signals toxicity
Leg vs arm blood pressure	Legs equal to or higher than arms	Arms higher than legs suggests coarctation
SpO2, single-ventricle infant on prostaglandin E1	75% to 85%	Extra oxygen dilates pulmonary vessels and steals systemic flow
Morphine for a tet spell	0.1 mg/kg IV, subcutaneous or IM as prescribed	Reduces hyperpnea and outflow tract spasm
Formula	Standard 20 kcal/oz; concentrated to 24 kcal/oz or more as prescribed	More calories in less volume
Feeding time	30 minutes or less	Longer feedings exhaust the infant and raise oxygen demand

Common exam traps

Choosing furosemide or digoxin for a tet spell: wrong because the problem is right ventricular outflow obstruction with right-to-left shunting, not fluid overload.
Choosing to limit fluids in a cyanotic child: wrong because polycythemia plus dehydration raises the risk of thrombosis and stroke.
Choosing to expect clubbing or cyanosis with an unrepaired VSD: wrong because a left-to-right shunt sends oxygenated blood back to the lungs.
Choosing oxygen to raise SpO2 above 92% in hypoplastic left heart syndrome on prostaglandin: wrong because it lowers pulmonary resistance and reduces systemic perfusion.
Choosing to repeat a digoxin dose the infant vomited: wrong because the absorbed amount is unknown and toxicity risk rises.

What to teach

Feed small amounts every 2 to 3 hours with rest periods, using the prescribed high-calorie formula; report sweating with feeds, fast breathing and poor weight gain.
For a tet spell, hold the infant in the knee-chest position, stay calm and call 911 if the color does not improve.
Prevent dehydration: call the provider the same day for fever, vomiting or diarrhea.
Keep teeth and gums healthy; antibiotics before dental procedures are given only for unrepaired cyanotic defects, prosthetic material in the first 6 months after repair, residual defects at a repair site and prosthetic valves.

Try 2 NCLEX-style questions on this topic

From the NCLEXPace question bank. Pick your answers, then check them inside NCLEXPace.

Question 1 · QID 87335710

A 4-month-old with unrepaired tetralogy of Fallot becomes agitated during a heel stick and develops deep, rapid breathing with dusky-blue lips; the SpO2 falls from a baseline of 84% to 62%. The nurse immediately places the infant in the knee-chest position and gives 100% oxygen by face mask, but after 5 minutes the cyanosis and hyperpnea persist. Which prescribed medication should the nurse administer next?

Select the best answer.

A. Morphine 0.1 mg/kg IV
B. Furosemide 1 mg/kg IV
C. Digoxin 10 mcg/kg orally
D. Albuterol 2.5 mg by nebulizer

Question 2 · QID 3D2DC170

The nurse assesses a 4-month-old with a large ventricular septal defect that has not yet been repaired. Which findings should the nurse expect? Select all that apply.

A. Respiratory rate of 66/min while resting
B. Sweating on the forehead while bottle-feeding
C. Rounded, bulbous fingertips (clubbing)
D. Two hospitalizations for pneumonia since birth
E. Blue color of the lips and tongue during crying
F. Weight that has fallen from the 40th to the 5th percentile

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Sources

Hockenberry MJ, Duffy EA, Gibbs KD. Wong's Nursing Care of Infants and Children. 12th ed. Elsevier; 2024.
Wilson WR, Gewitz M, Lockhart PB, et al. Prevention of Viridans Group Streptococcal Infective Endocarditis: A Scientific Statement From the American Heart Association. Circulation. 2021;143(20):e963-e978.

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