Congenital Cardiovascular Anomalies
Introduction
Congenital anomalies of the heart and blood vessels arise during the 1st 10 wk of embryonic development and are present at birth. The incidence is 1/120 live births; estimated risk is 2 to 3% in children with an affected 1st-degree relative.
About 5% of patients have a chromosomal abnormality (eg, trisomy 13, 18, or 21, Turner's syndrome); other anomalies may be part of a genetic syndrome (eg, Holt-Oram syndrome). Other possible causes are maternal illnesses (eg, diabetes mellitus, SLE, rubella), environmental exposure (eg, to thalidomide or alcohol [fetal alcohol syndrome]), or a combination. Usually, no specific cause is identified.
Pathophysiology
Congenital heart anomalies are classified as acyanotic or cyanotic, and acyanotic anomalies are classified as left-to-right shunts or obstructive lesions Some anomalies, particularly when severe, may cause heart failure (HF).
Left-to-right shunts: Oxygenated blood from the left heart (left atrium or left ventricle) or the aorta shunts to the right heart (right atrium or right ventricle) or the pulmonary artery through an abnormal opening between the 2 sides. Blood flows from left to right initially because BPs are normally higher on the left side. The additional blood on the right side increases pulmonary blood flow and pulmonary artery pressure to a varying degree. The greater the increase, the more severe the symptoms; a small left-to-right shunt is usually asymptomatic.
High-pressure shunts (those at the ventricular or great artery level) become apparent several days to a few weeks after birth; low-pressure shunts (atrial septal defects) become apparent considerably later. If untreated, elevated pulmonary artery pressure may lead to Eisenmenger's syndrome. A large left-to-right shunt (eg, large ventricular septal defect [VSD], patent ductus arteriosus) decreases lung compliance, leading to frequent lower respiratory tract infections.
Obstructive lesions: Blood flow is obstructed without shunting, causing a pressure gradient across the obstruction. The resulting pressure overload proximal to the obstruction may cause ventricular hypertrophy and HF. The principal manifestation is a heart murmur, which results from turbulent flow through the obstructed (stenotic) point. Examples are congenital aortic stenosis, which accounts for 3 to 6% of congenital heart anomalies, and congenital pulmonary stenosis, which accounts for 8 to 12% .
Cyanotic heart anomalies: Varying amounts of deoxygenated venous blood are shunted to the left heart, reducing systemic arterial O2 saturation. If there is > 5 g/dL of deoxygenated Hb, cyanosis (bluish discoloration of the skin, mucous membranes, and nails) results. Detection of cyanosis may be delayed in infants with dark pigmentation. Complications of persistent cyanosis include polycythemia, clubbing, thromboembolism, bleeding disorders, and hyperuricemia. Hypercyanotic spells frequently occur in infants with tetralogy of Fallot.
Depending on the anomaly, pulmonary blood flow may be increased (often resulting in HF), normal, or reduced (manifesting with severe cyanosis). Heart murmurs are variably audible and are not specific.
Heart failure: Some congenital heart anomalies (eg, bicuspid aortic valve, mild aortic stenosis) do not significantly alter hemodynamics. Others cause pressure or volume overload, sometimes producing HF. HF occurs when cardiac output is insufficient to meet the body's metabolic needs or when the heart cannot adequately dispose of venous return, causing pulmonary congestion (in left ventricular failure), edema primarily in dependent tissues and abdominal viscera (in right ventricular failure), or both. HF in infants and children has many causes other than heart anomalies.
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