Ostium secundum atrial septal defect

An ostium secundum defect represents the persistence of the foetal foramen ovale.

Because of the greater distensibility of the right atrium, blood flows from the left to the right through the defect. This allows recirculation of blood through the lungs and back to the left side of the heart.

The extra burden of pumping is taken by the right ventricle.

Ostium secundum defects are more common than ostium primum defects.

Patent foramen ovale (PFO) is the most common congenital heart abnormality of fetal origin and is present in approximately ~25% of the worldwide adult population.

PFOs may be causative of stroke in certain patients whose stroke is otherwise cryptogenic (2)

• evidence suggests that percutaneous closure reduces the subsequent risk of stroke in appropriately selected patients, with a large relative benefit but small absolute benefit

Approximately 50% of patients 60 years or younger with an embolic stroke of undetermined source (cryptogenic stroke) have a PFO, compared with 25% of the general population.

Reference:

1. Homma S et al. Patent foramen ovale.Ther Adv Neurol Disord. 2019 May 24
2. Mac Grory B, Ohman E M, Feng W, Xian Y, Yaghi S, Kamel H et al. Advances in the management of cardioembolic stroke associated with patent foramen ovale BMJ 2022; 376 :e063161 doi:10.1136/bmj-2020-063161
3. Kent DM, Wang AY. Patent Foramen Ovale and Stroke: A Review. JAMA. Published online July 28, 2025.