8.4 Acyanotic Congenital Heart Lesions, Patent Ductus Arteriosus, Obstructed TAPVR & Neonatal Heart Failure

Acyanotic Heart Lesions, PDA, Obstructed TAPVR & Neonatal Heart Failure

Sections 8.1 and 8.2 cover ductal-dependent lesions, where closing the ductus is fatal. This section covers lesions that cause trouble through too much pulmonary blood flow (left-to-right shunts), along with one cyanotic emergency that is often misdiagnosed as lung disease.

Left-to-Right Shunt Physiology

At birth, pulmonary vascular resistance (PVR) is still relatively high. Over the first weeks, PVR falls toward adult levels. As it falls, blood takes the easier path through a septal defect or ductus into the lungs. Qp (pulmonary flow) rises above Qs (systemic flow), which causes:

• Pulmonary overcirculation and edema (tachypnea, retractions, crackles)
• Left atrial and ventricular volume overload (cardiomegaly, gallop)
• Increased work of breathing and metabolic demand, leading to poor feeding, sweating with feeds, and failure to thrive

Timing matters on the exam: A large VSD is often quiet on day 1. Symptoms typically appear at about 4–8 weeks, when PVR has fallen. A newborn in shock on day 1 with a "VSD" should prompt a search for another lesion.

Oxygen can make shunt lesions worse

Oxygen is a pulmonary vasodilator. In a large shunt, high FiO2 lowers PVR further and increases pulmonary overcirculation, worsening edema and stealing systemic flow. Titrate oxygen to the saturation target set with cardiology, often in the low-to-mid 90s for acyanotic shunts and 75–85% for single-ventricle physiology (Section 8.2).

The Patent Ductus Arteriosus in the Preterm Infant

In preterm infants, the ductus often stays open because the immature ductal tissue is sensitive to prostaglandins and responds less to oxygen. A hemodynamically significant PDA (hsPDA) shunts left to right as PVR falls, typically in the first week.

Signs:

• Bounding peripheral pulses and a wide pulse pressure (low diastolic pressure)
• Active precordium and a systolic or continuous murmur (sometimes silent when very large)
• Increasing ventilator or oxygen needs, pulmonary edema, and pulmonary hemorrhage
• Systemic steal: Low diastolic pressure reduces flow to gut, kidneys, and brain, contributing to oliguria, feeding intolerance, and NEC risk

Management (receiving NICU decisions, supported in transport):

• Adequate PEEP helps limit pulmonary overcirculation and edema.
• Avoid fluid overload, and keep hematocrit in the target range.
• Pharmacologic closure uses NSAIDs (indomethacin or ibuprofen) or acetaminophen. Contraindications for NSAIDs include active bleeding, significant thrombocytopenia, renal failure, and NEC.
• Surgical ligation or catheter closure for refractory cases.

Remember the opposite situation: In ductal-dependent lesions (Sections 8.1–8.2), the ductus must be kept open with PGE1. Never give NSAIDs or acetaminophen for "PDA closure" until a ductal-dependent lesion has been excluded by echocardiography.

Obstructed Total Anomalous Pulmonary Venous Return (TAPVR)

In TAPVR, all pulmonary veins drain into the systemic venous circulation instead of the left atrium. When that pathway is obstructed (classically infracardiac drainage below the diaphragm), pulmonary venous blood backs up:

• Severe cyanosis with pulmonary edema (diffuse ground-glass or reticular opacities) and often a small heart on radiograph
• Respiratory failure and shock in the first hours or days of life
• Easily mistaken for RDS, pneumonia, or PPHN. An echocardiogram is essential when "lung disease" responds poorly or when saturations are similar pre- and post-ductally.

Management: Obstructed TAPVR is a surgical emergency. PGE1 does not relieve the pulmonary venous obstruction, and increasing pulmonary blood flow can worsen edema. Transport focuses on ventilation with PEEP, inotropic support, correcting acidosis, and getting the infant to a cardiac surgical center quickly. Some teams arrange ECMO as a bridge.

Neonatal and Infant Heart Failure

Heart failure in infants rarely looks like adult heart failure. Signs include:

• Tachypnea and tachycardia at rest
• Poor feeding, sweating with feeds, and poor weight gain
• Hepatomegaly (the infant's equivalent of peripheral edema; a liver edge more than 2–3 cm below the costal margin)
• Gallop rhythm, cool extremities, and cardiomegaly on radiograph

Causes by timing:

• First days: Ductal-dependent systemic lesions (as the ductus closes), critical aortic stenosis, cardiomyopathy (including hypertrophic cardiomyopathy in infants of diabetic mothers), large arteriovenous malformations (vein of Galen), myocarditis, and prolonged SVT (Section 8.3)
• Weeks 4–8: Large left-to-right shunts

Transport management:

1. Avoid large fluid boluses. Give 5–10 mL/kg aliquots only if hypovolemia is likely, and reassess liver size and lungs after each.
2. Give diuretics (for example, furosemide) for pulmonary edema when perfusion allows.
3. Provide inotropic support (milrinone, dobutamine, or low-dose epinephrine; Section 6.1) for low output.
4. Use positive pressure and PEEP. They reduce left ventricular afterload and pulmonary edema but can lower preload, so watch blood pressure after intubation.
5. Titrate oxygen to targets rather than maximizing it in shunt lesions.
6. Consider PGE1 if a ductal-dependent systemic lesion is possible. A newborn in cardiogenic shock in the first two weeks has one until proven otherwise (Section 8.2).