Congenital Heart Disease — Tetralogy of Fallot

A 2-year-old girl with known Tetralogy of Fallot presents to the emergency department with severe cyanosis, loss of consciousness, and convulsions. Her SpO₂ is 45% despite high-flow oxygen. The parents report she had a prolonged crying episode 30 minutes ago. On examination, she has a harsh systolic murmur at the left sternal border and a single loud S2. Arterial blood gas shows pH 7.18, PaCO₂ 32 mmHg, HCO₃⁻ 12 mEq/L, and PaO₂ 38 mmHg. What is the most likely cause of her acute deterioration?

Regarding the surgical management and hemodynamic changes in Tetralogy of Fallot, all of the following are true EXCEPT:

A 6-month-old infant with uncorrected Tetralogy of Fallot is scheduled for surgery in 2 weeks. The child has had two cyanotic spells in the past month. Which drug is the preferred agent for prophylaxis of cyanotic spells in the preoperative period?

A 3-year-old boy with Tetralogy of Fallot presents with a cyanotic spell characterized by sudden onset of dyspnea, increased cyanosis, and syncope during play. Which drug is the first-line agent for acute management of this hypercyanotic episode?

A 2-month-old infant born to non-consanguineous parents presents with severe cyanosis (SpO₂ 65%) and poor feeding. Echocardiography confirms tetralogy of Fallot with severe right ventricular outflow tract obstruction. The parents inquire about the presence of associated genetic syndromes. Which investigation is most appropriate to screen for chromosomal and genetic abnormalities in this neonate?