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Ann Thorac Surg 1997;63:198-201
© 1997 The Society of Thoracic Surgeons

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Original Articles: General Thoracic

Right-to-Left Interatrial Shunt After Pneumonectomy

Departments of Internal Medicine, Cardiothoracic Surgery, and Pulmonary Critical Care and Medicine, The Cleveland Clinic Foundation, Cleveland, Ohio

Accepted for publication August 5, 1996.

	Abstract

Top Footnotes Abstract Introduction Case Reports Patient 2 Patient 3 Patient 4 Comment References

 
Background. Platypnea and Orthodeoxia have been described with congenital heart and severe lung diseases.

Methods. We report 4 patients in whom platypnea and orthodeoxia developed after pneumonectomy. In these patients the mean oxygen saturation on room air was 65% (range, 45% to 79%) in the supine position. On O₂ therapy it improved to 94% (range, 80% to 99%). When the patients assumed the erect position and were receiving O₂ therapy the saturation dropped to a mean of 76% (range, 56% to 82%) and the patients complained of shortness of breath. Cardiac catheterization revealed a mean pulmonary capillary wedge pressure of 11.6 mm Hg (range, 7 to 18 mm Hg). All patients had normal right atrial pressure. A right-to-left interatrial shunt through a patent foramen ovale was documented by transesophageal echocardiography and dynamic ultrafast magnetic resonance imaging. The patients underwent surgical closure of the patent foramen ovale.

Results. In the erect position, the room air O₂ saturation improved to a mean of 95% (range, 92% to 99%), and the shortness of breath disappeared.

Conclusions. Postpneumonectomy patients complaining of shortness of breath should be assessed for platypnea and orthodeoxia. A right-to-left interatrial shunt through a patent foramen ovale can occur even in the absence of elevated right heart pressures, especially after right pneumonectomy, and is accentuated in the upright posture. Surgical correction of the patent foramen ovale can produce dramatic improvement.

	Introduction

Top Footnotes Abstract Introduction Case Reports Patient 2 Patient 3 Patient 4 Comment References

 
Shortness of breath after pneumonectomy is most commonly due to loss of alveolar volume, restriction of the vascular bed, chest wall pain, and diaphragmatic dysfunction [1]. Right-to-left interatrial shunt (RLIAS) with normal right heart pressures after the procedure is a rare cause, with only a few reported cases in the literature. Such an RLIAS may be found in patients who have a patent foramen ovale (PFO) and have undergone pneumonectomy. A diagnostic clue in this situation is shortness of breath on assuming an upright posture (platypnea), with symptoms being relieved by recumbency. Additionally, significant oxygen desaturation may develop while the patient is upright (orthodeoxia), with oxygen tension improving after the patient lies down. This condition can be easily diagnosed with the help of transesophageal or contrast echocardiography or magnetic resonance imaging, including dynamic ultrafast imaging [1]. Additionally, the diagnosis can also be made with the aid of a physiologic shunt study, as well as cardiac angiography [2, 3]. We report 4 cases of platypnea and orthodeoxia developing after a right pneumonectomy as a result of RLIAS through a PFO in the presence of normal right atrial pressure.

	Case Reports

Top Footnotes Abstract Introduction Case Reports Patient 2 Patient 3 Patient 4 Comment References

 
Patient 1
A 75-year-old man was hospitalized on April 12, 1994, with shortness of breath, especially in the upright position, and dyspnea on exertion. In October 1993, he had undergone a right pneumonectomy for squamous cell carcinoma. The patient subsequently experienced progressive shortness of breath beginning in January 1994. His exercise tolerance decreased markedly, and he was only able to walk approximately 6 m. A chest computed tomographic scan with contrast performed at an outside hospital revealed a large clot in the right pulmonary artery stump, which was confirmed on pulmonary arteriography, suggesting that recurrent pulmonary emboli to the left lung were responsible for his symptoms. The patient had been placed on home oxygen therapy with 5 L/min via a nasal cannula. Pulmonary function tests performed in February 1994 revealed moderate restrictive impairment with a somewhat disproportionate reduction in the diffusing capacity. No evidence of obstruction was noted. Room air arterial blood gas analysis in March 1994 revealed a pH of 7.44, carbon dioxide tension of 26 mm Hg, oxygen tension of 43 mm Hg, and oxygen saturation of 79%. The oxygen saturation remained 79% to 81% on 5 L of oxygen. The ventilation-perfusion scans performed in March 1994 showed heterogeneous uptake in the remaining lung without any defects, and were suggestive of chronic obstructive pulmonary disease.

On admission, the patient was tachypneic with a respiratory rate of 26 breaths/min. There was no cyanosis on supplemental oxygen by nasal cannula. Chest and cardiac examination results were unremarkable. Arterial blood gas analysis with the patient in a supine position, receiving 5 L/min of oxygen, revealed a pH of 7.43, carbon dioxide tension of 15 mm Hg, oxygen tension of 145 mm Hg, HCO₃ of 10 mEq/L, and oxygen saturation of 99%.

In view of a known right pulmonary artery stump clot, we initially placed the patient on intravenous heparin therapy. Subsequently, repeat ventilation-perfusion scans were found to be of low probability for pulmonary emboli; early uptake of the isotope in the kidneys raised the possibility of a right-to-left shunt. As the patient had undergone right pneumonectomy, a diagnosis of platypnea/orthodeoxia secondary to RLIAS was entertained. Transesophageal echocardiography with contrast demonstrated a large PFO. Cardiac catheterization confirmed the PFO, atherosclerotic heart disease, and left ventricular hypertrophy with normal systolic function. The PFO was noted to be stretched, and there was shunting of inferior vena caval blood directly into the left atrium despite normal right atrial pressure. Catheterization readings were as listed in Table 1.

The patient had an uncomplicated postoperative course. His platypnea/orthodeoxia resolved, and postoperative arterial blood gas analysis before discharge revealed a pH of 7.47, carbon dioxide tension of 29 mm Hg, oxygen tension of 71 mm Hg, HCO₃ of 21 mEq/L, and oxygen saturation of 95% on room air.

	Patient 2

Top Footnotes Abstract Introduction Case Reports Patient 2 Patient 3 Patient 4 Comment References

 
A 59-year-old patient had progressive development of dyspnea over 1 month. He had undergone right pneumonectomy for adenocarcinoma 4 months earlier. He became acutely dyspneic with severe respiratory distress. Arterial blood gas analysis on 100% nonrebreather mask revealed an oxygen tension of 27 mm Hg and carbon dioxide tension of 37 mm Hg. The patient was intubated and ventilated, and administration of heparin was started for clinical suspicion of pulmonary emboli.

Chest radiography showed opacification of the right hemithorax with emphysematous changes on the left. Electrocardiography showed no evidence of acute myocardial infarction. Ventilation and perfusion scans were indeterminate for pulmonary emboli. The patient underwent left pulmonary angiography, which showed no evidence of pulmonary emboli and no arteriovenous malformation. The mean pulmonary artery pressure was 17 mm Hg. Heparin administration was stopped, and as his oxygenation improved, he was extubated.

It was noted that the patient was short of breath, cyanotic, and having a pulse oxygen saturation of less than 75% even on 100% oxygen through a face mask in a sitting posture. A diagnosis of platypnea/orthodeoxia secondary to RLIAS was entertained. Transesophageal echocardiography revealed an atrial septal defect (ASD), with the atrial septum bowing to the left. The color contrast study documented RLIAS, and cardiac catheterization was performed (Table 2).

	Patient 3

Top Footnotes Abstract Introduction Case Reports Patient 2 Patient 3 Patient 4 Comment References

 
A 65-year-old patient was admitted with progressive shortness of breath. He had undergone right pneumonectomy for large cell carcinoma. His symptoms were worse in the upright position and were somewhat relieved on lying down. On examination he was tachycardiac and had central cyanosis; there was no evidence of cardiac failure. Chest examination was consistent with the history of right pneumonectomy. Cardiac examination revealed the position of maximal impulse shifted to the right, and there were no murmurs or gallops.

Electrocardiographic results were normal. Arterial blood gas analysis on room air with the patient in a sitting position revealed an arterial oxygen tension of 38 mm Hg. On an inspired oxygen fraction of 1.0, the arterial oxygen tension improved to 50 mm Hg, which further improved to 80 mm Hg when the patient assumed a supine position.

A right-to-left shunt was suspected and was estimated to be 27% using the indirect Fick's equation. The patient had normal right heart pressures, with pulmonary artery pressures of 28 to 32/8 to 12 mm Hg (mean, 18 mm Hg). A perfusion lung scan showed no perfusion defect but a high uptake over kidneys and brain, suggesting the presence of a right-to-left shunt. An RLIAS was diagnosed by dynamic ultrafast magnetic resonance imaging [1].

The patient underwent an open heart operation and the PFO was corrected. Postoperative recovery was uneventful, and arterial blood gas analysis on room air showed an arterial oxygen tension of 92 mm Hg.

	Patient 4

Top Footnotes Abstract Introduction Case Reports Patient 2 Patient 3 Patient 4 Comment References

 
A 67-year-old patient was admitted with the complaint of shortness of breath on exertion. He had undergone right pneumonectomy 1 year earlier for a large cell carcinoma of the lung. He was more short of breath in the upright position than lying down. His physical examination results were consistent with the history of right pneumonectomy.

A chest radiograph showed opacification of the right lung with shifting of the mediastinum to the right. The left lung was normal. The electrocardiogram was normal.

The arterial blood gas analysis showed an oxygen tension of 47 mm Hg on room air; on an inspired oxygen fraction of 1.0, it improved to only 56 mm Hg. A right-to-left shunt was suspected, and the shunt fraction was calculated to be 27%. The patient underwent transthoracic echocardiography with agitated saline solution and transesophageal echocardiography, both of which confirmed an RLIAS due to a PFO.

The patient underwent transcatheter closure of the PFO. He made a good recovery, and his symptoms improved, with an arterial oxygen tension of 88 mm Hg on room air.

	Comment

Top Footnotes Abstract Introduction Case Reports Patient 2 Patient 3 Patient 4 Comment References

 
Dyspnea and hypoxemia after pneumonectomy with normal clinical and radiologic findings in the remaining lung can be due to chronic obstructive pulmonary disease, thromboembolic disease, airway narrowing, respiratory muscle weakness, and right-to-left shunting [4]. Platypnea and orthodeoxia have most commonly been described with congenital heart and severe lung diseases [5]. Platypnea/orthodeoxia from RLIAS with normal right heart pressures is a rare complication after pneumonectomy, having only 18 case reports in the English-language literature, the present study included. One of the cases included in this report has been previously reported [1].

The exact pathophysiology responsible for the development of platypnea and orthodeoxia in patients after pneumonectomy is poorly understood. Patients in whom this complication developed had a previously undiagnosed PFO or ASD, and the RLIAS developed in the face of normal right-sided pressures [2]. Patients' symptoms resolve after surgical repair of the PFO or ASD [2]. Schnabel and associates [6] in 1956 were the first to report development of an RLIAS despite normal right-sided pressures in a patient after a right pneumonectomy. In that case and in the majority of subsequent cases, similar characteristics were found. First, there generally appeared to be a symptom-free period between the operation and the occurrence of the first complaints of 1 to 5 months. Second, the dyspnea and right-to-left shunt were related to the patient's position, being more severe in the upright position than in the recumbent position (platypnea). Third, the shunt became greater with volume depletion. Further, the majority of the patients had undergone a right pneumonectomy [2].

Begin [5] postulated that platypnea and orthodeoxia occurring after right pneumonectomy were due the pressure gradient across the ASD that was induced by restriction of the pulmonary vascular bed and by the weight of the resulting right-sided hydrothorax on the right atrium. He also theorized that the vertical position caused a decrease in the mixed venous oxygen saturation because of a fixed right-to-left shunt. The worsening hypoxemia generated a cycle of elevated right heart pressure, and thereby increased the gradient for the right-to-left shunt. He also speculated that the fluid in the right hemithorax compressed the right atrium and further increased the right-sided intracardiac pressures [7]. Begin's theory invokes the necessity of a pressure gradient for the shunt flow. However, it has been demonstrated that the right-to-left shunting can occur in the absence of such a gradient [1, 2, 7–11].

LaBresh and associates [12] have postulated that right-to-left shunting through an ASD occurs secondary to changes in the relationship of right and left ventricular compliance, with the right ventricle becoming less compliant (ie, stiffer) than the left. It was stated that pneumonectomy can affect atrial emptying either directly by altering the normal anatomy or indirectly by changing relationship in ventricular compliance. Shunting across an ASD occurs primarily during diastole and is determined by the difference between left and right ventricular compliance, with shunting from the less compliant (stiffer) to the more compliant chamber [12]. Normally right atrial pressure is lower than the mean left atrial pressure. During early diastole and isovolumetric contraction of the right ventricle, the right atrial pressure could be slightly higher than the left atrial pressure [13]. During these phases of the cardiac cycle, a small right-to-left shunt has been documented in patients with an uncomplicated ASD [2]. The reversal of the mean interatrial pressure gradient could be due to increased right ventricular afterload, which results from the increased pulmonary vascular resistance caused by the reduced pulmonary vascular bed after pneumonectomy. This subsequently can cause elevation of the right ventricular end-diastolic pressure, thereby lowering right ventricular compliance and increasing right atrial pressures. Additionally, right-to-left shunting could be accentuated by inspiration, because inspiration elevates right-sided pressures by increasing right ventricular preload as well as right ventricular afterload [2].

In 1 case report, there was resolution of platypnea with only replacement of blood volume in a hypovolemic patient. Surgical repair of the septal defect was not required in this case. It was thought that the platypnea was caused by a decrease in cardiac output in the upright position, which was further exacerbated by hypovolemia, leading to an increase in venous desaturation. Under these circumstances, the presence of the RLIAS was more significant [14].

Smeenk and associates [11] noticed that, in patients with an ASD, the right-to-left shunt is more apt to occur when the defect is located low in the septum. Altered anatomic relations between the inferior vena cava, the superior vena cava, and the atrial septum, especially after right pneumonectomy, can cause preferential flow from the inferior vena cava through a PFO and ASD, even in the absence of a pressure gradient [1, 10]. In 2 of our 4 patients it was well documented that the heart was markedly rotated to the right and displaced posteriorly. It has been postulated that in this situation, streaming of the inferior vena caval blood directly into the left atrium takes place as the atrial orifice straddles the limbus of the vessel [2]. Additionally, the weight of the heart in the shifted position pulls downward on the interatrial septum, causing the foramen ovale to open or widen [2]. Such "streaming" has been documented angiographically [7, 9]. Postpneumonectomy mediastinal distortion may also lead to shift of the right atrium while the inferior vena cava remains fixed in position; this may open the previously closed foramen ovale.

It can be appreciated that the exact mechanism for the development of platypnea/orthodeoxia and RLIAS after pneumonectomy in patients with previ- ously asymptomatic PFO or ASD is not completely clear. We believe, depending on the clinical situation, each theory may have a role. However, streaming of blood from right to left in an upright position seems to explain the picture in the majority of patients. Probe patency of the foramen ovale in the general population has been cited to be anywhere from 16% to 35%, based on autopsy data [2, 4, 8, 11]. Taking into account the increased number of pulmonary resections performed at this time, it is possible that this complication occurs more frequently than suspected, possibly in a less clinically apparent form, making it more difficult to recognize [2]. This complication should be considered in any patient in whom postpneumonectomy dyspnea or hypoxemia develops. Workup should begin with confirming right-to-left shunt using a shunt study (Fick's equation). If ventilation-perfusion lung scanning is being considered to rule out pulmonary emboli, looking for early uptake on the kidneys or brain could further strengthen the suspicion. An interatrial defect could be easily documented by transesophageal echocardiography.

	Footnotes

Top Footnotes Abstract Introduction Case Reports Patient 2 Patient 3 Patient 4 Comment References

 
Address reprint requests to Dr Mehta, Department of Pulmonary Medicine and Critical Care, The Cleveland Clinic Foundation, One Clinic Center, Cleveland, OH 44195.

	References

Top Footnotes Abstract Introduction Case Reports Patient 2 Patient 3 Patient 4 Comment References

 

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2. Smeenk FWJM, Postmus PE. Interatrial right-to-left shunting developing after pulmonary resection in the absence of elevated right sided heart pressures. Review of the literature. Chest 1993;103:528–31.[Abstract/Free Full Text]
3. Roos CM, Romijn KH, Braat CP, Van Leeuwen AM. Posture dependent dyspnea and cyanosis after pneumonectomy. Eur J Respir Dis 1981;62:377–82.[Medline]
4. Berry L, Braude S, Hogan J. Refractory hypoxemia after pneumonectomy: diagnosis by transesophageal echocardiography. Thorax 1992;47:60–1.[Abstract/Free Full Text]
5. Begin R. Platypnea after pneumonectomy. N Engl J Med 1975;293:342–3.[Medline]
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10. Springer RM, Gheorghiade M, Chakko CS, et al. Platypnea and interatrial right-to-left shunting after lobectomy. Am J Cardiol 1983;51:1802–3.[Medline]
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13. Levin AR, Spach MS, Boineau JP, Canent RV, Capp MP, Jewett PH. Atrial pressure dynamics in atrial septal defect (secundum type). Circulation 1968;37:476–88.[Abstract/Free Full Text]
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