Right-dominant arrhythmogenic cardiomyopathy complicated by platypnea-orthodeoxia syndrome: a novel mechanism of patent foramen Ovale-mediated hypoxaemia: a case report.

Background: Platypnea-orthodeoxia syndrome (POS) is a rare but treatable cause of positional hypoxaemia, typically associated with intracardiac shunting. We present the first documented case of POS secondary to patent foramen ovale (PFO) in a patient with right-dominant arrhythmogenic cardiomyopathy (ACM). Case summary: A 48-year-old male with right-dominant ACM developed progressive dyspnoea and upright hypoxaemia. Workup examinations revealed atrial flutter and PFO with right-to-left shunting. PFO occlusion resolved hypoxaemia, with sustained improvement at 3-year follow-up despite progressive RV dysfunction. Discussion: This case represents a rare form of POS attributable to the coexistence of PFO and right-dominant ACM. The pathophysiological mechanism underlying POS in this case might be parallel to that observed in right ventricular myocardial infarction or ischaemia in which elevated right-sided intracardiac pressures due to impaired RV output secondary to right heart dysfunction equals or surpasses left heart pressure which created a pressure gradient favourable for right-to-left shunting (RLS) through the PFO in upright position. Based on comprehensive clinical evaluation, PFO closure was ultimately performed. Conclusion: This case highlights right-dominant ACM as a novel predisposing factor for POS via PFO shunting. The pathophysiological mechanism underlying POS in this case might be parallel to that observed in right ventricular myocardial infarction or ischaemia. PFO closure may be curative for right-dominant ACM-related hypoxaemia and POS.