INTRODUCTION: The mechanism of right to left shunting of blood though a patent foramen ovale (PFO) in the absence of elevated right-sided pressures is controversial.
CASE PRESENTATION: A 79 year-old female was admitted to our institution due to acute ischemic stroke. Her hospital course was complicated by Clostridium difficile colitis with megacolon, requiring left hemicolectomy. 2 months into her hospitalization, she experienced recurrent attacks of shortness of breath and cyanosis whenever she assume a sitting position. Physical examination was only remarkable for a moderate thoracic kyphoscoliosis. When supine and while breathing room air pulse oximetry showed oxyhemoglobin saturation of 95%. After few minutes of sitting in a chair, she became cyanotic and her oxygen saturation decreased to 82% and did not improve with 100% oxygen, however, it was completely normalized when she resumed a supine position. Her chest roentogram and electrocardiogram were normal. A chest computed tomographic angioscan showed no evidence of pulmonary embolism or intrapulmonary arteriovenous malformations. A transthoracic echocardiography study combined with agitated saline injection (Figure 1) confirmed the presence of a PFO with preferential opening during the sitting position. Arterial blood gases was measured at various inclines (0, 30, 60 and 90°) while breathing 100% oxygen with a tightfitting non-rebreathing mask to calculate the shunt fraction (Figure 2). Right heart catheterization revealed an isolated positional changes in right atrial pressure from 2 mm H2O (supine) to 8 mm H2O (sitting) with normal right ventricle and pulmonary artery pressures. Patient was seen six weeks after transcutaneous closure of the PFO where she was asymptomatic and had normal oxygen saturations during both supine and erect positions.
DISCUSSIONS: Orthodeoxia-platypnea syndrome has been reported in association with different cardiac, pulmonary, and extrathoracic conditions, however, it is most commonly associated with an interatrial right-to-left shunt through a PFO, atrial septal defect (ASD), or fenestrated atrial septal aneurysm usually in the presence of pulmonary hypertension (1). The mechanism of intracardiac right to left shunt in the absence of pulmonary hypertension is still controversial and several mechanisms have been proposed. First, an isolated increase in right atrial pressure may reverse the interatrial gradient and can be due to an external compression of the right atrium or decreased right ventricular or right atrium compliance(2–8). Second, several conditions (atrial septal distortion and horizontalization, persistent Eustachian valve, or a high atrial septal defect) may lead to preferential blood flow streaming directly to the left atrium (3,7,9,10). We demonstrated an isolated preferential elevation in the right atrial pressure during upright position. This phenomenon has been proposed as a possible mechanism for a right to left shunt despite normal right-sided pressure. To our knowledge, this is the first case in the English literature to confirm this association and to document a proportional relationship between the degree of body inclination and the amount of right to left shunt. The combined effect of an elongated aorta and kyphoscoliosis may have contributed to the selective stretching and opening of the patent foramen ovale during the erect position in our patient as well as to the increase in right atrial pressure. Although both conditions may have been present for a long time in this patient, her recent major abdominal surgery may have worsened her intrathoracic geometry probably by manipulation of the aorta.
CONCLUSION: In patients with PFO and normal pulmonary pressures, right to left shunt may occur due to an isolated positional increase in the RA pressures.
DISCLOSURE: Saleh Alazemi, No Financial Disclosure Information; No Product/Research Disclosure Information