3.2 Congenital Heart Defects

Congenital Heart Defects & Emergency Management

Congenital Heart Defects (CHDs) represent the most common category of major birth defects, occurring in approximately 8 per 1,000 live births. In the emergency department, pediatric nurses encounter infants with undiagnosed structural heart disease presenting in acute circulatory collapse as the fetal ductus arteriosus closes, as well as older children with known CHD presenting in acute decompensation. Understanding structural anatomy, shunting dynamics, and hypercyanotic spell management is essential for CPEN success.

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Classification of Congenital Heart Defects

Structural cardiac anomalies are classified functionally based on blood flow patterns and systemic oxygenation:

                          ┌─────────────────────────────────────┐
                          │     Congenital Heart Defects        │
                          └──────────────────┬──────────────────┘
                                             │
                   ┌─────────────────────────┴─────────────────────────┐
                   ▼                                                   ▼
     ┌───────────────────────────┐                       ┌───────────────────────────┐
     │     Acyanotic Defects     │                       │     Cyanotic Defects      │
     │  (Left-to-Right Shunting)  │                       │  (Right-to-Left Shunting)  │
     └─────────────┬─────────────┘                       └─────────────┬─────────────┘
                   │                                                   │
        ┌──────────┴──────────┐                             ┌──────────┴──────────┐
        ▼                     ▼                             ▼                     ▼
┌───────────────┐     ┌───────────────┐             ┌───────────────┐     ┌───────────────┐
│ Increased Pulm│     │ Obstructive   │             │ Decreased Pulm│     │ Mixed Blood   │
│ Blood Flow    │     │ Lesions       │             │ Blood Flow    │     │ Flow          │
│ (VSD, ASD,    │     │ (Coarctation, │             │ (Tetralogy of │     │ (Transposition│
│  PDA)         │     │ Aortic Steno) │             │  Fallot, TA)  │     │  of Great Art)│
└───────────────┘     └───────────────┘             └───────────────┘     └───────────────┘

Acyanotic Defects (Left-to-Right Shunts & Obstructions)

Oxygenated blood from the left side of the heart is shunted back into the right side and pulmonary circulation. Oxygen saturation remains normal (>95%), but pulmonary blood flow is volume-overloaded.

• Clinical Presentation: Tachypnea, intercostal retractions, poor feeding, diaphoresis during feeding, failure to thrive, hepatomegaly, and pulmonary congestion.
• Long-Term Risk: Untreated left-to-right shunting causes chronic pulmonary hypertension, eventually reversing the shunt to right-to-left (Eisenmenger syndrome), producing irreversible cyanosis.

Cyanotic Defects (Right-to-Left Shunts & Mixed Lesions)

Deoxygenated systemic venous blood bypasses the lungs and enters systemic arterial circulation directly, causing persistent arterial hypoxemia (SpO2 70–85%).

• Clinical Presentation: Central cyanosis (mucous membranes, trunk), polycythemia (elevated hematocrit to compensate for chronic hypoxia), digital clubbing, and metabolic acidosis.
• Hyperoxia Test: Administering 100% oxygen fails to significantly increase arterial oxygen tension (PaO2 remains <150 mmHg), confirming a right-to-left cardiac shunt rather than primary pulmonary parenchymal disease.

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Major Structural Defects & Clinical Profiles

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Duct-Dependent Cardiac Lesions & Prostaglandin E1

Certain neonatal CHD structural anomalies rely on an open Ductus Arteriosus to maintain either systemic blood flow (duct-dependent systemic flow: Coarctation of Aorta, Hypoplastic Left Heart Syndrome) or pulmonary blood flow (duct-dependent pulmonary flow: Pulmonary Atresia, severe TGA).

As the ductus arteriosus naturally closes within the first 24 to 72 hours of life, these neonates present in severe cardiogenic shock, profound cyanosis, metabolic acidosis, and collapse.

Prostaglandin E1 (Alprostadil) Administration

• Mechanism: Keeps the ductus arteriosus patent or reopens a recently closed ductus to re-establish life-sustaining perfusion.
• Dosing: Initial IV/IO infusion rate of 0.05 to 0.1 mcg/kg/min. Once ductal patency is achieved, titrate down to the lowest effective maintenance dose (0.01–0.02 mcg/kg/min).
• Adverse Effects & Nursing Vigilance:
  • Apnea: Occurs in up to 10–12% of neonates receiving PGE1. Elective endotracheal intubation equipment must be immediately available at the bedside prior to initiating infusion.
  • Fever & Vasodilation: Cutaneous flushing, severe hypotension, and hyperthermia are common; manage hypotension with volume boluses.

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Hypercyanotic "Tet" Spells Management

Hypercyanotic spells ("Tet" spells) occur in children with Tetralogy of Fallot. They are acute paroxysms of severe cyanosis, hyperpnea, and agitation caused by a sudden increase in Right Ventricular Outflow Tract (RVOT) infundibular spasm or a drop in Systemic Vascular Resistance (SVR). This causes a dramatic surge in right-to-left shunting across the VSD, sending deoxygenated blood into systemic circulation.

Emergency Nursing Intervention Sequence

Step 1: Knee-to-Chest Position ➔ Step 2: 100% Oxygen & Comfort ➔ Step 3: Morphine Sulfate IV
                                                                         │
Step 6: Phenylephrine IV ◄─── Step 5: Sodium Bicarbonate IV ◄─── Step 4: IV Fluid Bolus (10-20 mL/kg)

1. Place Infant in Knee-to-Chest Position (or have older child squat): First immediate action. Squatting or flexing knees to chest compresses the femoral arteries, dramatically increasing Systemic Vascular Resistance (SVR). Higher SVR forces blood out of the right ventricle into the high-resistance pulmonary artery rather than shunting across the VSD into the aorta.
2. Administer 100% Supplemental Oxygen: Use a non-rebreather mask. Oxygen is a potent pulmonary vasodilator that lowers pulmonary vascular resistance (PVR) while treating arterial hypoxemia.
3. Provide Calm, Comforting Environment: Agitation increases endogenous catecholamines, worsening RVOT infundibular spasm. Minimize painful procedures and hold the child.
4. Administer Morphine Sulfate: Dosage 0.1 mg/kg IV/IM/SC. Morphine suppresses the central respiratory drive, reduces anxiety, and directly relaxes the infundibular cardiac muscle spasm.
5. Administer Isotonic IV Fluid Bolus: Administer 10 to 20 mL/kg normal saline. Volume expansion increases right ventricular preload and filling pressure, improving blood flow across the stenotic pulmonary valve.
6. Administer Sodium Bicarbonate: Dosage 1 to 2 mEq/kg IV. Treats systemic metabolic acidosis resulting from severe hypoxia.
7. Administer Phenylephrine: Dosage 0.005 to 0.02 mg/kg IV. Phenylephrine is a pure alpha-1 adrenergic agonist that increases SVR if the spell is refractory to position and morphine.