Hypoxaemia associated with an enlarged aortic root: a new syndrome?

Abstract

Objective: To assess the mechanisms through which an enlarged aortic root may facilitate right to left shunting through a patent foramen ovale. Patients: 19 patients with the platypnoea-orthodeoxia syndrome (POS) were compared with 30 control patients without platypnoea. Interventions: Multiplane transoesophageal echocardiography. Main outcome measures: The aortic root diameter, atrial septal dimension behind the aortic root, and amplitude of the phasic oscillation of the septum were measured. Four groups of patients were compared: 12 platypnoeic patients with a dilated aortic root (POS-D), 7 platypnoeic patients with a normal aortic root (POS-N), 15 control patients with a dilated aortic root (CONT-D), and 15 control patients with a normal aortic root (CONT-N). Results: In POS-D and CONT-D patients, the apparent atrial septal dimension was 16.3 (2.7) mm and 17.4 (5.9) mm respectively, compared with 24.4 (5.2) mm in POS-N patients and 25 (4) mm in CONT-N (p , 0.005). Furthermore, the amplitude of septal oscillation was 14.7 (2.5) mm in the POS-D group versus 5.8 (2.4) mm in CONT-N (p , 0.001) compared with 23.3 (3) mm in seven patients with an atrial septal aneurysm (p ,0.001). Conclusion: Patients with an enlarged aorta have an apparently smaller dimension and increased mobility of the atrial septum. These findings appear to result from compression by the aortic root and decreased septal tautness. Consequently, a ''spinnaker effect'' with the inferior vena caval flow may take place, opening the foramen ovale and leading to sustained right to left shunting.A patent foramen ovale (PFO) is a defect in the atrial septum that results from incomplete fusion of the septum primum to the septum secundum. The persistence of a PFO into adulthood may lead to several complications, including paradoxical embolism of thrombus, air or tumoural material, and refractory hypoxaemia.Normally, even if a potential channel between the atria remains, the higher left atrial pressure keeps the flap-like valve of the foramen ovale opposed to the septum secundum. Most cases of sustained right to left shunting through a PFO are seen in situations where right atrial pressure exceeds that of the left, forcing open the potentially patent foramen ovale.However, right to left shunting can be less often observed in the absence of any demonstrable pressure gradient between right and left atria. Right to left shunting despite normal right atrial pressure has been reported after right pneumonectomy 1 2 or in association with venous embryonic remnants. 3 4 In these situations, an altered relation between the caval veins and the atrial septum presumably accounts for flow related rather than pressure related shunting.A few cases of aneurysm of the ascending aorta associated with right to left shunting across a PFO have been reported, 5-10 but evidence for a non-fortuitous association is still lacking. Therefore, we conducted a study to further analyse factors facilitating right to left shunting in patients with PFO, with particular attention paid to t...

Platypnea-Orthodeoxia Syndrome With Atrial Septal Defect and Ectatic Aortic Root: A Case Report and Review of the Literature

“…In the presence of this last condition, orthostatism could stretch the interatrial communication, augmenting the flow through the shunt or it could displace the atrial septum towards the horizontal position directing the blood flow from the inferior vena cava to the atrial septum, thereby extending the shunt [1,9,14,15].…”

“…Such an enlargement seems to be able to alter atrial septal geometry promoting a more direct pathway for the blood to flow from the vena cava to the interatrial communication or making the interatrial septum more mobile and permeable if there is an underlying defect [14,15].…”

Platypnea-orthodeoxia Syndrome Caused by a Latent Atrial Septal Defect

“…Therefore, additional anatomical or functional factors are required for the development of a right to left shunt. In most cases, platypnea-orthodeoxia syndrome due to an intracardiac shunt is associated with an enlarged ascending aorta (6). It has been hypothesized that the ascending aorta causes an anterior-posterior displacement of the aortic root when the patient is in the upright position, which leads to compression of the right atrium and an enlargement of the PFO aperture (7).…”

“…It has been hypothesized that the ascending aorta causes an anterior-posterior displacement of the aortic root when the patient is in the upright position, which leads to compression of the right atrium and an enlargement of the PFO aperture (7). The bulging of the aortic root above the tricuspid orifice may behave functionally like an acquired cor triatriatum dexter (6). A previous report has described a large aneurysm of the ascending aorta that caused a significant lateral displacement of the superior vena cava (SVC) and considerable compression of the right atrium, thus leading to the development of a direct shunt between the vena cava and the left atrium across a PFO (8).…”

Diagnosing and understanding the mechanisms behind orthodeoxia syndrome

“…There is a strong association of ascending aortic aneurysms and orthodeoxia in the presence of an interatrial defect, with a prevalence of over 60% being reported. 2 Although it is not clearly known how an enlarged aortic root can lead to this phenomenon, postulated mechanisms include deformation of the RA by the enlarged aorta causing preferential flow-directed shunting from the inferior vena cava (IVC). 3 Laybourn et al 4 suggested that enlargement of the ascending aorta induced a counterclockwise rotation of the heart in the upright position, thereby allowing preferential IVC flow through a distorted atrial septum.…”