Exercise-Induced Desaturation in Patent Foramen Ovale: Mechanisms, Diagnostic Approach, and Resolution After Closure—A Narrative Review with an Illustrative Case

Exercise-induced desaturation is an uncommon but clinically significant manifestation of patent foramen ovale, which is present in approximately one-quarter of the general population. Although patent foramen ovale is usually asymptomatic, exertion may provoke transient right-to-left shunting when dynamic changes in venous return and intrathoracic pressure favour intermittent right-to-left transit across the interatrial septum. This narrative review synthesises current evidence on exertion-provoked shunting and its contribution to otherwise unexplained dyspnoea and hypoxaemia. To illustrate these concepts, we present an illustrative case with marked exercise-induced desaturation in the absence of pulmonary disease. The evaluation combined contrast transthoracic and transoesophageal echocardiography with cardiopulmonary exercise testing, and the shunt magnitude was quantified invasively using catheter-based thermodilution at rest and during Valsalva provocation. Six months after percutaneous closure, repeat cardiopulmonary exercise testing showed complete resolution of exercise-induced desaturation without a statistically significant change in exercise tolerance (work performed). Notably, normalisation of oxygen saturation during exercise may occur without a measurable increase in maximal exercise capacity. Overall, patent foramen ovale-mediated right-to-left shunting is an under-recognised yet potentially reversible cause of exertional hypoxaemia; diagnosis typically requires deliberate physiological provocation and integrated imaging, and closure can be considered in carefully selected individuals.