Cardiovascular · UKMLA & AKT
Atrial septal defect (ASD)
A free high-yield preview for the UKMLA Applied Knowledge Test, covering how to recognise this condition. The full SA Note notes add investigations, management and complications, with practice questions on this topic.
Key high-yield points
- Often asymptomatic in childhood - detected as incidental murmur
- Dyspnoea and fatigue - reduced systemic output, increased pulmonary flow
- Palpitations - AF/flutter from chronic atrial dilatation
- Stroke or TIA - paradoxical embolism: DVT crosses ASD into systemic circulation when right atrial pressure transiently exceeds left (Valsalva, coughing) or permanently in Eisenmenger syndrome
- Cyanosis and clubbing - late sign, indicates Eisenmenger syndrome (right-to-left shunt reversal)
- Ejection systolic murmur - upper left sternal border (pulmonary area); caused by increased flow across pulmonary valve, not flow through the ASD itself
- Fixed splitting of S2 - hallmark sign; right heart is volume-overloaded throughout the cycle, so pulmonary valve closure is delayed regardless of respiratory phase
In an uncomplicated ASD the shunt is left-to-right - patients are NOT cyanotic. Cyanosis and clubbing = Eisenmenger syndrome with shunt reversal. This distinction is a frequent exam trap.
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