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Orthodeoxia Caused by an Aortic Aneurysm and Atrial Septal Aneurysm with Reversal of Shunt After Myocardial Infarction

Drexel University, Philadelphia, PA

INTRODUCTION: Orthodeoxia, arterial desaturation during upright posture improved by recumbency, is a rare physical finding. We present an unusual case of orthodeoxia caused by an aortic aneurysm compressing the right atrium, resulting in an intermittent right to left shunt through an inter-atrial septal aneurysm with reversal of the shunt after myocardial infarction.

CASE PRESENTATION: A 78-year-old male presented to the emergency room with several months of dizziness, which worsened whenever he stood up and bent over to pick up his morning paper. He denied any loss of consciousness, chest pain, or shortness of breath. A CT of the head and cardiac enzymes were negative. During his hospitalization, he acutely desaturated, requiring a 100% non-rebreather mask with a PaO2 of 38 mmHg. Further testing revealed a negative V/Q scan; a helical chest CT was negative for pulmonary embolism but showed a thoracoabdominal aortic aneurysm; an echocardiogram showed preserved left ventricular function and a possible inter-atrial aneurysm. He was transferred to a tertiary care center for possible repair of his aortic aneurysm. The patient’s exam was significant for absent jugular venous distention, clear lungs, regular heart rate without murmurs, and no lower extremity edema or calf swelling. He was discovered to have orthodeoxia, with oxygen saturations of 95% supine and 78% sitting upright while receiving 5 L/min nasal oxygen. The orthodeoxia was postulated to be caused by extrinsic compression of his dilated aortic arch causing intermittent, positional shunting through the interatrial aneurysm. While undergoing right heart catherization, the patient developed ventricular tachycardia with hypotension requiring electrical cardioversion and intubation. No pulmonary hypertension was present. The patient continued to be unstable and underwent emergent cardiac catheterization that showed a 98% occlusion of his left anterior descending artery, which required angioplasty and stent placement. A subsequent transesophageal echocardiogram showed an enlarged left atrium and left ventricle, and a newly decreased ejection fraction of 35%. The patient no longer had orthodeoxia and was discharged without further surgical intervention.

DISCUSSIONS: Orthodeoxia is arterial desaturation with an upright posture, which is improved by recumbency. The orthodeoxia-platypnea syndrome is very rare with only about 50 case reports in the literature. The differential diagnosis includes pulmonary arteriovenous malformations, intracardiac shunt, hepatopulmonary syndrome, recurrent pulmonary emboli, chronic lung disease, and post-pneumonectomy syndromes[1].Normally, small inter-atrial defects create a left to right shunt due to the higher filling pressures of the left atrium as compared to the right atrium. However, there have been reports of an elongated aorta, aortic aneurysm, or dilated aorta causing extrinsic compression of the right atrium, which elevated the right atrial pressure resulting in a right to left shunt in the presence of an interatrial defect. These patients underwent surgical correction of the aortic and interatrial defects with subsequent resolution of their orthodeoxia[2,3]. Our patient was unique, because his shunt was corrected by an acute myocardial infarction, which resulted in decreased left ventricular function and an increased left atrial pressure, thus reversing the right to left shunt. Since he was subsequently asymptomatic and no longer produced a positional right to left shunt, surgical repair of his atrial defect was deferred at this time.

CONCLUSION: Orthodeoxia can be caused by an extrinsically compressing aorta combined with an inter-atrial defect in the setting of normal pulmonary artery pressures. We report a novel case of reversal of orthodeoxia after myocardial infarction, without surgical intervention.

DISCLOSURE: A.G. Ko, None.

REFERENCES

1. Cheng, T. Mechanisms of platypnea-orthodeoxia: what causes water to flow uphill? Circulation.2002; 105-6 :47 .
2. Savage E, et al. Intermittant hypoxia due to right atrial compression by an ascending aortic aneurysm. Ann Thorac Surg.1996; 62 :582 –3.
3. Popp G, et al. Platypnea-orthodeoxia related to aortic elongation. Chest.1997; 112(6) :1682 –4.