Central cyanosis: cardiac causes (some cardiac conditions can be placed in more than one category)
| Problem | Mechanism | Presentation and investigations |
|---|---|---|
| Right-to-left shunts: Tetralogy of Fallot (ToF) Severe/critical pulmonary stenosis (PS) Pulmonary atresia (PA) with or without ventricular septal defect (VSD) Ebstein anomaly (with interatrial communication) Persistent pulmonary hypertension of the newborn (PPHN) | Increased right heart pressure, often secondary to right ventricular outflow tract obstruction or persistence of the fetal circulation (PPHN), leads to diminution or reversal of the usual systemic-to-pulmonary pressure gradient. An atrial or ventricular septal defect ±PDA permits right-to-left shunting, thereby allowing desaturated blood into the systemic circulation, resulting in cyanosis | History: may have antenatal diagnosis; features of fetal distress likely in PPHN; may be cyanotic from birth; significant deterioration or circulatory collapse following ductal closure in duct-dependent pulmonary circulation (as in critical PS). Examination: possible syndromic features (eg, 22q11 deletion); cyanosis, low saturations with possible discrepancy in preductal and postductal saturations (as in PPHN); increased intensity (PPHN) or absence (PA) of the pulmonary component to the second heart sound (P2); murmur reflecting underlying defect(s). CXR: abnormal cardiac silhouette (size and shape); hypoplasia/absence of the main pulmonary artery (‘pulmonary artery bay’); possible right aortic arch; oligaemic lung fields. Gas: low pO2; possible metabolic/lactic acidosis. Echocardiogram: diagnostic; important to delineate presence of PDA and direction of ductal flow during cardiac cycle |
| Common mixing: Total anomalous pulmonary venous connection (TAPVC) Common atrium Any single ventricle, for example, hypoplastic left heart syndrome (HLHS). Truncus arteriosus (common arterial trunk) | Desaturated systemic venous blood and oxygenated pulmonary venous blood are allowed to freely mix at the atrial level (as in TAPVC or tricuspid atresia), at the ventricular level (as in double-inlet ventricles), or at the arterial level (as in truncus arteriosus), thereby desaturating the systemic arterial blood. Systemic arterial oxygen saturations are directly proportional to pulmonary bloodflow | History: may have antenatal diagnosis (unlikely in TAPVC); cyanosed from birth; respiratory distress where pathophysiology results in pulmonary congestion (as in obstructed TAPVC). Rapid deterioration or circulatory collapse ensues when: (1) systemic circulation is reliant on mixing via an interatrial communication (eg, tricuspid atresia, TAPVC) that is too small (‘restrictive’). The basis for the balloon atrial septostomy; (2) the arterial duct closes where the systemic circulation is duct-dependent. Examination: reflects underlying defect(s) and presence of coexisting anomalies; possible syndromic features; may be cyanotic from birth; possible features of low cardiac output. CXR: Reflects underlying defect(s) and coexisting anomalies—may be dextrocardia and abdominal situs inversus; abnormal cardiac silhouette; lung fields may be oligaemic, plethoric (eg, un-obstructed TAPVC) or there may be pulmonary venous congestion (as in obstructed TAPVC). Gas: low pO2; metabolic/lactic acidosis if haemodynamic compromise. Echocardiogram: diagnostic; important to delineate presence of interatrial communication, size and direction/velocity of bloodflow across; and presence of PDA and direction of ductal flow during cardiac cycle |
| Transposition of the great arteries (TGA) | Parallel systemic and pulmonary circulations where deoxygenated blood recirculates through the systemic circulation and oxygenated blood recirculates through the pulmonary circulation. Left-to-right (systemic-to-pulmonary) flow across a PDA increases pulmonary bloodflow*, thereby increasing left atrial pressure, facilitating left-to-right flow across an interatrial communication, which ultimately permits passage of oxygenated blood into the systemic circulation | History: may have antenatal diagnosis; generally cyanosed from birth; circulatory collapse in the absence of a defect allowing mixing, when the interatrial communication is restrictive, or following ductal closure; if large VSD may become breathless when pulmonary vascular resistance drops. Examination: desaturated preduct and postduct with cyanosis; possible features of low cardiac output if restrictive interatrial communication or congestive cardiac failure if large VSD; no murmur in the absence of associated defects such as VSD with PS ; often large babies. CXR: Can be normal at birth. An ‘egg-shaped’ heart with narrow mediastinum is classically described; pulmonary plethora is seen when a large ductus or a VSD is present. Gas: low pO2 with low saturations; metabolic/lactic acidosis if haemodynamic compromise; high incidence of hypoglycaemia. Echocardiogram: diagnostic (ventriculo-arterial discordance); important to note presence of associated defects (ie, VSD, PS); important to delineate presence of interatrial communication, size and direction/velocity of blood flow across; important to delineate presence of PDA |
*The basis for maintaining ductal patency with prostaglandin in TGA, and not, as commonly misconceived, to permit shunting of oxygenated blood (from the PA in TGA) into the systemic circulation, which would defy the pressure gradient.