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Re: Platypnea-orthodeoxia syndrome associated with aortic root dilatation is not a new syndrome

Dear Editor,

I read with interest the article on hypoxemia associated with aortic root dilatation.[1] But this is not a new syndrome as Eicher et al.[1] suggested. It is the platypnea-orthodeoxia syndrome first described in 1949 by Burchell et al.[2] Platypnea-orthodeoxia is a relatively uncommon but often underdiagnosed syndrome [3] with striking clinical manifestations, characterized by dyspnea relieved by assumption of a supine position and simultaneous deoxygenation following a change from a recumbent to an upright position.

In 1949, Burchell and his colleagues from Mayo Clinic [2] described a patient with a post-traumatic intrathoracic venous-arterial type of blood shunt, who exhibited a threefold increase in ventilation and a 15-point decrease in arterial oxygen saturation whenever the patient was in an upright position. They actually did not use the term platypnea- orthodeoxia in their presentation. It was Altman and Robin [4] who coined the term platypnea in 1969. Everybody had been familiar with the term ‘orthopnea’ that was used to describe increased dyspnea in the recumbent position relieved by sitting, which is, of course, a well-known, common and important symptom of congestive heart failure. So Altman and Robin [4] coined the term ‘platypnea’ or flat breathing, which is the reverse symptom of dyspnea in an upright position relieved by recumbency. Then in 1976 Robin and coworkers [5] introduced and added the second term ‘orthodeoxia’ to this syndrome to describe accentuated arterial deoxygenation following a change to an upright position from recumbency.

The most common etiological association in platypnea-orthodeoxia nowadays is an interatrial right-to-left shunt, through either a patent foramen ovale or an atrial septal defect or a fenestrated atrial septal aneurysm. Under normal conditions, an interatrial communication allows blood to shunt from left to right, due to a higher pressure in left atrium than right atrium and a greater compliance of the right ventricle than the left ventricle. Right-to-left interatrial shunting is usually associated only with spontaneous or induced pulmonary hypertension. Therefore, in the absence of a right-to-left pressure gradient, what is the mechanism for a right-to-left shunt? Or put in another way, what causes water to flow uphill [6]? Of course, a persistent Eustachian valve can cause interatrial right-to-left shunting with a normal right atrial pressure.[7]

Platypnea-orthodeoxia could be explained on the basis of positional modification of abnormal shunting. Standing upright could stretch the interatrial communication, be it a patent foramen ovale, an atrial septal defect, or a fenestrated atrial septal aneurysm, thus allowing more streaming of venous blood from inferior vena cava through the defect, whether or not a persistent Eustachian valve coexists.[8,9] This redirection of flow caused by an anatomic distortion of the right atrium or the atrial septum also might occur from aortic root dilatation or aneurysm. An example of the former was nicely demonstrated on transesophageal echocardiography in 2001 by Medina et al.[10]

Due to space constraint, I would not discuss all the other causes of platypnea-orthodeoxia. I refer your readers to my original Editorial Comment that was published in Catheterization and Cardiovascular Interventions in May 1999.[11] Suffice to say that two conditions must coexist to cause platypnea-orthodeoxia: (1) an anatomical component in the form of an interatrial communication and (2) a functional component which produces a deformity in the atrial septum and results in a redirection of shunt flow with the assumption of an upright posture.

References

1. Eicher J-C, Bonniaud P, Baudouin N, et al: Hypoxaemia associated with an enlarged aortic root: a new syndrome? Heart 2005;91:1030-1035.

2. Burchell HB, Helmholz HF Jr, Wood EH: Reflex orthostatic dyspnea associated with pulmonary hypotension. Am J Physiol 1949;159:563-564.

3. Cheng TO: Platypnea-orthodeoxia and blockpnea as two unrecognized or underdiagnosed causes of medically unexplained dyspnea. Chin Med J 2004;117:1116.

4. Altman M, Robin ED: Platypnea (diffuse Zone I phenomenon)? N Engl J Med 1969;281:1347-1348.

5. Robin ED, Laman D, Horn BR, Theodore J: Platypnea related to orthodeoxia caused by true vascular lung shunts. N Engl J Med 1965;294:941-943.

6. Cheng TO: Mechanism of platypnea-orthodeoxia: what causes water to flow uphill? Circulation 2002;105:e47.

7. Bashour T, Kabbani S, Saalouke M, Cheng TO: Persistent Eustachian valve causing severe cyanosis in atrial septal defect with normal right heart pressures. Angiology 1983;34:79-83.

8. Cheng TO: reversible orthodeoxia. Ann Intern Med 1992;116:875.

9. Cheng TO: Platypnea-orthodeoxia due to interatrial right-to-left shunting. Acta Cardiologica 1994;49:217.

10. Medina A, Suarez de Lezo J, Cabarello E, et al: Platypnea-orthodeoxia due to aortic elongation. Circulation 2001;104:741.