Acyanotic Congenital Heart Defects

Acyanotic congenital heart defects are structural cardiac malformations that do not typically produce clinically apparent cyanosis, at least not at initial presentation.

They include left-to-right shunt lesions and obstructive lesions:

• ventricular septal defect, atrial septal defect, and patent ductus arteriosus, which together are the commonest congenital heart defects overall
• coarctation of the aorta and aortic and pulmonary valve stenosis

In the shunt lesions, blood flows from the higher-pressure systemic (left-sided) circulation to the lower-pressure pulmonary (right-sided) circulation. This produces pulmonary overcirculation. If left uncorrected it leads over time to progressive pulmonary vascular disease and, reversal of shunt direction.

This is Eisenmenger syndrome. The resulting cyanosis is a late, serious, and largely preventable complication of chronically uncorrected, significant left-to-right shunting.

Pathophysiology and classification

• Ventricular septal defect, the commonest congenital heart defect overall, produces left-to-right shunting across the defect during systole. Clinical significance is directly related to defect size.
• Small defects are haemodynamically insignificant, frequently close spontaneously over the first years of life, and need no intervention. Large defects produce significant pulmonary overcirculation, heart failure, and failure to thrive if not addressed.
• Atrial septal defect produces left-to-right shunting at the atrial level. The pressure gradient is relatively lower, so the course is generally more gradual and insidious than in ventricular septal defect.
• It is frequently clinically silent through childhood and may present later, sometimes in adulthood, with right heart volume overload, arrhythmia or, in longstanding uncorrected cases, pulmonary hypertension.
• Patent ductus arteriosus is failure of normal physiological closure of the ductus arteriosus after birth. It produces continuous left-to-right shunting from the aorta to the pulmonary artery throughout the cardiac cycle. Significance again relates to shunt size.
• It is more prevalent in premature infants, in whom the ductus is less mature, anatomically and physiologically, and less likely to close spontaneously.
• Coarctation of the aorta is a discrete narrowing of the aorta, typically near the ductal insertion site. It is an obstructive lesion producing differential blood pressure and pulse character between the upper and lower body.
• Severe coarctation in the newborn period is duct-dependent for systemic blood flow to the lower body. There is a critical risk of rapid deterioration as the ductus closes in severe cases presenting in early infancy. The duct-dependent circulation principle is detailed under cyanotic congenital heart defects.

• Small, haemodynamically insignificant shunt lesions are frequently asymptomatic and identified incidentally by a murmur on routine examination.
• Larger, significant shunts produce symptoms of pulmonary overcirculation and heart failure: tachypnoea, poor feeding, diaphoresis with feeding, faltering growth, and recurrent respiratory tract infections.
• These typically become apparent over the first weeks to months of life. Pulmonary vascular resistance falls physiologically after birth, progressively increasing the left-to-right shunt.
• A murmur is a common and important presenting or incidental finding. Its character and location guide diagnosis.
• Ventricular septal defect gives a harsh, pansystolic murmur at the lower left sternal edge. Atrial septal defect gives a soft, systolic ejection murmur with fixed splitting of the second heart sound. Patent ductus arteriosus gives a continuous, "machinery" murmur.
• Absence of a murmur does not exclude significant pathology. In a large ventricular septal defect the pressure gradient, and so the murmur, may be relatively less prominent.
• Coarctation of the aorta characteristically shows radiofemoral delay (a palpable delay between the radial and femoral pulses) and a significant blood pressure differential between the upper and lower limbs.
• Severe coarctation presenting in early infancy as a duct-dependent lesion causes critical systemic hypoperfusion and shock as the ductus closes. Milder cases may present later in childhood or even adulthood with hypertension or, less commonly, symptoms from the obstruction itself.
• Failure to thrive and recurrent respiratory infections are important, common presenting features of significant shunt lesions in infancy. They reflect pulmonary overcirculation, increased work of breathing, and increased metabolic demand from the cardiac workload.

• Antenatal ultrasound screening and routine newborn examination are important parts of the diagnostic pathway, with principles similar to those under cyanotic congenital heart defects.
• Newborn examination includes careful auscultation for a murmur and assessment of femoral pulses, a standard component aimed specifically at identifying coarctation of the aorta.
• Echocardiography is the definitive diagnostic investigation for any suspected congenital heart defect. It gives detailed anatomical characterisation and assesses the haemodynamic significance of the lesion. It guides management, including the need for and timing of surgical or interventional treatment.
• Four-limb blood pressure measurement, comparing upper and lower limb pressures, supports diagnosis and assessment of severity in suspected coarctation of the aorta, together with careful assessment of femoral pulse character.
• Chest radiography may show cardiomegaly and increased pulmonary vascular markings with a significant left-to-right shunt. Electrocardiography may show chamber hypertrophy patterns relevant to the lesion. Both are supportive, not definitive, alongside echocardiography.

• Small, haemodynamically insignificant shunt lesions, particularly small ventricular septal defects and small patent ductus arteriosus, are frequently managed by watchful waiting and serial echocardiographic surveillance, because spontaneous closure over the first years of life is substantially likely.
• Intervene for lesions that fail to close spontaneously and remain haemodynamically significant, or that have specific additional complications. These include a small but recognised risk of infective endocarditis with certain lesion types and, for ventricular septal defect, the risk of aortic valve prolapse with certain defect locations.
• Larger, haemodynamically significant shunts with symptomatic heart failure and failure to thrive need medical management of heart failure (diuretics and, where relevant, additional heart failure therapy) as a bridge to definitive treatment.
• Definitive treatment is surgical or, increasingly, transcatheter device closure. The approach and timing are individualised to the lesion, its size, and the infant's clinical status.
• Patent ductus arteriosus is a distinct clinical challenge in premature infants. In appropriately selected premature infants it may be closed pharmacologically with a cyclooxygenase inhibitor (indomethacin or ibuprofen), which inhibits the prostaglandin-mediated mechanism maintaining ductal patency.
• Surgical or transcatheter closure is reserved for cases not responding to pharmacological treatment or where it is not appropriate.
• Atrial septal defect has a more indolent natural history than ventricular septal defect. Once intervention is decided, it is frequently managed with transcatheter device closure, typically in later childhood. This is less invasive than surgery and is now preferred for anatomically suitable defects.
• Coarctation of the aorta presenting as a critical, duct-dependent lesion in early infancy needs prostaglandin E1 infusion to maintain ductal patency and preserve lower body perfusion pending surgical repair. This is the same emergency principle as detailed under cyanotic congenital heart defects.
• Definitive treatment is surgical repair or, in some cases, balloon angioplasty with or without stenting, which is particularly relevant for recurrent coarctation after previous repair.
• Milder coarctation presenting later in childhood or adulthood is generally managed with elective surgical or transcatheter intervention. Manage any associated hypertension, which may persist even after successful anatomical repair.
• Long-term cardiology follow up addresses surveillance for any residual lesion and long-term complications specific to the defect and its treatment. These include recoarctation risk after coarctation repair and hypertension surveillance, since hypertension persists in a proportion of patients despite successful anatomical correction.
• Provide developmental and psychosocial support. Women reaching reproductive age need pregnancy-related counselling, as addressed under cyanotic congenital heart defects.
• The great majority of these conditions now carry an excellent long-term prognosis with contemporary management.