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Dr. Kerr is Assistant Professor of Medicine and Dr. Rubin is Professor of Medicine, Pulmonary Vascular Center and Division of Pulmonary and Critical Care Medicine, University of California, San Diego, School of Medicine.
Correspondence to: Lewis J. Rubin, MD, FCCP, Pulmonary Vascular Center and Division of Pulmonary and Critical Care Medicine, University of California, San Diego, School of Medicine, 9300 Campus Point Dr, La Jolla, CA 92037; e-mail: ljrubin{at}ucsd.edu
Despite major advances in the medical treatment of chronic pulmonary artery hypertension, only one form of this condition is potentially curable. At experienced centers, the performance of pulmonary thromboendarterectomy (PTE) for the treatment of patients with chronic thromboembolic pulmonary hypertension (CTEPH) results in restoration of normal or near-normal pulmonary hemodynamics, even in the presence of severe pulmonary hypertension or right-sided heart failure.1 2 The risk of recurrence is low, since patients generally have preoperative placement of an inferior vena cava filter and are treated indefinitely with oral anticoagulants once surgery has been performed.3
The management of CTEPH patients requires a skilled multidisciplinary team consisting of physicians to participate in preoperative assessment and postoperative care, surgeons and anesthesiologists with expertise in intraoperative techniques of endarterectomy and extracorporeal cardiopulmonary support, and a nursing staff that has been trained in the care of these patients during a sometimes challenging postoperative course. Persistent pulmonary hypertension from residual, organized thrombi or inoperable small vessel arteriopathy4
and reperfusion pulmonary edema5
are the most difficult and life-threatening postoperative events. At centers with experience performing PTE, a mortality rate of 
5% has been quoted,1
2
which is a remarkable achievement when one considers the severity of the cardiopulmonary disease and the hemodynamic fragility of these patients. The greatest risk is in those patients with the highest levels of pulmonary vascular resistance, particularly when right ventricular function is severely impaired.6
In this issue of CHEST (see page 338), Nagaya and colleagues report their experience using continuous IV epoprostenol (prostacyclin, Flolan; GW USA Inc; Research Triangle, NC) as a "medical bridge" to stabilize such patients prior to their undergoing PTE. Their study was not a randomized trial, rather, the patients were selected for epoprostenol therapy based on the severity of their hemodynamic condition and their increased risk of death with PTE. The epoprostenol-treated patients manifested significant hemodynamic improvement with a course of therapy that averaged less than 2 months’ duration, and all except one patient survived the surgery and had an excellent hemodynamic result.
Prostacyclin and its analogs have been demonstrated to improve the signs and symptoms of pulmonary hypertension due to a variety of conditions, including primary pulmonary hypertension,7 pulmonary arterial hypertension associated with connective tissue diseases,8 portal-pulmonary hypertension, HIV-associated pulmonary hypertension, and Eisenmenger syndrome.9 In addition to its potent vasodilating effect and its inhibition of platelet aggregation properties, prostacyclin has antiproliferative properties that appear to be important for its long-term effects in patients with pulmonary hypertensive diseases.10 Although acute vasodilatation in response to prostanoid administration has been observed in patients with CTEPH, it is likely that the platelet antiaggregatory and antiproliferative effects of prostacyclin, perhaps combined with a direct inotropic effect, account for the hemodynamic improvement observed by Nagaya et al. The time course of improvement observed by Nagaya et al is similar to that seen when epoprostenol is used to treat other forms of pulmonary hypertension.7 8 9
The observations by Nagaya et al are intriguing, and provide a rationale for the further study of the preoperative treatment of high-risk CTEPH patients with epoprostenol. However, this study does not answer a key question. Did the patients treated with epoprostenol survive because they had a successful surgery, or did they have a successful operation because of receiving treatment with epoprostenol? A randomized trial will be necessary to determine whether preoperative epoprostenol treatment improves mortality in high-risk patients undergoing thromboendarterectomy, particularly those who have a less complete postoperative hemodynamic result than that reported in this series. The study also raises several questions. (1) Does epoprostenol therapy worsen the reperfusion pulmonary edema that occurs after successful PTE? The authors gradually weaned patients from epoprostenol therapy over a 1-week period postoperatively, yet permanent discontinuation once cardiopulmonary bypass is initiated may be considered as an alternative. We employ this approach at our center for patients with pulmonary hypertension who are receiving epoprostenol and undergo lung transplantation in an attempt to minimize postimplantation injury. (2) Are new, less invasive treatment modalities that are effective in patients with other forms of pulmonary hypertension comparably effective in the preoperative management of CTEPH? Bosentan (Actelion; Allschwil, Switzerland; and Genentech; South San Francisco, CA), the newly approved nonselective endothelin-receptor antagonist is orally active,11 and Iloprost is a prostacyclin analog that can be administered by nebulization.12 (3) Who are the best candidates for "epoprostenol bridge therapy," and what is the optimal period of therapy before performing PTE? These questions can be addressed by clinical trials at large medical centers that have expertise in treating patients with this condition.
The development of the surgical techniques for PTE was a major advance in the treatment of patients with CTEPH. We recognize the challenge, and welcome the opportunity, to improve the medical management of this condition as well.
References
This article has been cited by other articles:
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  N. S. Hill, I. R. Preston, and K. E. Roberts Inoperable Chronic Thromboembolic Pulmonary Hypertension: Treatable With Medical Therapy Chest, August 1, 2008; 134(2): 221 - 223. [Full Text] [PDF]
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 P. Bresser, J. Pepke-Zaba, X. Jais, M. Humbert, and M. M. Hoeper Medical Therapies for Chronic Thromboembolic Pulmonary Hypertension: An Evolving Treatment Paradigm Proceedings of the ATS, September 1, 2006; 3(7): 594 - 600. [Abstract] [Full Text] [PDF]
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L. J. Rubin, M. M. Hoeper, W. Klepetko, N. Galie, I. M. Lang, and G. Simonneau Current and Future Management of Chronic Thromboembolic Pulmonary Hypertension: From Diagnosis to Treatment Responses Proceedings of the ATS, September 1, 2006; 3(7): 601 - 607. [Abstract] [Full Text] [PDF]
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A. Peacock, G. Simonneau, and L. Rubin Controversies, Uncertainties and Future Research on the Treatment of Chronic Thromboembolic Pulmonary Hypertension Proceedings of the ATS, September 1, 2006; 3(7): 608 - 614. [Abstract] [Full Text] [PDF]
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