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J Thorac Cardiovasc Surg 2007;134:974-981
© 2007 The American Association for Thoracic Surgery

Evolving Technology

Clinical application of airway bypass with paclitaxel-eluting stents: Early results

^a Department of Surgery, Division of Thoracic Surgery, Santa Casa de Porto Alegre-Pavilhao Pereira Filho Hospital, Fundacao Faculdade Federal de Ciencias Medicas de Porto Alegre, Porto Alegre-RS, Brazil
^b Lung Transplant Service Allergy, Immunology and Respiratory Medicine, Alfred Hospital and Monash University, Victoria, Australia
^c Department of Thoracic Medicine, The Prince Charles Hospital, Brisbane, Australia
^d Klinik fur Innere Medizin, Pneumologie, Allergologie, Beatmungs und Umweltmedizi, Meizinische Universitatsklinik, Saarland, Germany
^e Department of Thoracic Surgery and Endoscopy, Ruhrlandklinik, Essen, Germany
^f Department of Respiratory Medicine, Tan Tock Seng Hospital, Singapore
^g Department of Respiratory & Critical Care Medicine, Singapore General Hospital, Singapore.

Read at the Eighty-sixth Annual Meeting of The American Association for Thoracic Surgery, Philadelphia, Pa, April 29–May 3, 2006.

Received for publication April 27, 2006; revisions received April 1, 2007; accepted for publication May 11, 2007.

^_* Address for reprints: Paulo F. G. Cardoso, MD, Ph.D., Santa Casa de Porto Alegre-Pavilhao Pereira Filho, Rua Prof. Annes Dias 285-1 PPF, Porto Alegre-RS, 90020-090, Brazil. (Email: cardosop{at}gmail.com).

	Abstract

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Objective: To assess the safety and early clinical results of a multicenter evaluation of airway bypass with paclitaxel-eluting stents for selected patients with severe emphysema.

Methods: Airway bypass was performed with a fiberoptic bronchoscope in three steps: identification of a blood vessel–free location with a Doppler probe at the level of segmental bronchi, fenestration of the bronchial wall, and placement of a paclitaxel-eluting stent to expand and maintain the new passage between the airway and adjacent lung tissue. All adverse events were recorded, as well as 1- and 6-month pulmonary function tests and dyspnea index.

Results: Thirty-five patients received the airway bypass procedure with a median of 8 stents implanted per patient. At 1-month follow-up, statistically significant differences in residual volume, total lung capacity, forced vital capacity, forced expiratory volume, modified Medical Research Council scale, 6-minute walk, and St George’s Respiratory Questionnaire were observed. At the 6-month follow-up, statistically significant improvements in residual volume and dyspnea were demonstrated. One death occurred after bleeding during the procedure. Retrospective analysis revealed that the degree of pretreatment hyperinflation may be an important indicator of which patients achieve the best short- and long-term results.

Conclusions: The airway bypass procedure reduces hyperinflation and improves pulmonary function and dyspnea in selected patients with severe emphysema. Duration of benefit appears to correlate with the degree of pretreatment hyperinflation. These preliminary clinical results support further evaluation of the procedure.

	Introduction

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Dr Cardoso

The irreversible destruction of lung parenchyma in emphysema is characterized by progressive air space enlargement within the lung and is associated with marked enhancement of collateral ventilation. The concept of collateral ventilation was first introduced by Van Allen, Lindskog, and Richter¹ in 1930. Collateral ventilation is inconsequential in normal human lungs; however, in emphysematous lungs it can be essential for ventilation distribution beyond the obstructed airways.² In emphysema, the resistance of the airways can exceed collateral resistance, forcing air to flow preferentially through collateral pathways, which may ultimately promote the redistribution of ventilation within the lungs.³ Revisiting this concept in 1978, Macklem⁴ proposed its potential clinical applicability for reducing gas trapping by venting the hyperinflated emphysematous lungs through spiracles—the creation of artificial passages from the lung surface to the outside of the chest. A recent revision of this lung deflation concept proposed bronchial fenestration for venting the emphysematous air spaces into the main airway, coining the term "airway bypass."⁵ Airway bypass is the process of creating extra-anatomic passages between the collaterally ventilated pulmonary parenchyma and larger airways, allowing trapped gas to exit from the lung. This decrease in gas trapping reduces hyperinflation, allowing better chest wall and diaphragmatic excursion and therefore improving dyspnea. The feasibility of airway bypass was first tested experimentally on ex vivo explanted native lungs obtained from patients with emphysema undergoing lung transplantation.⁶ This study demonstrated an improvement in the forced expiratory volumes in 1 and 5 seconds (FEV₁ and FEV₅), thus suggesting airway bypass as a potential therapeutic option for patients with marked hyperinflation and severe pulmonary destruction. These early clinical feasibility and safety studies in human lungs^5,7 recognized, but did not address, the need to develop the technology to improve long-term passage patency. Other laboratory research studied the value of combining stents with pharmaceuticals to inhibit tissue growth around the stent.⁷ This, in turn, resulted in the development of the paclitaxel-eluting stent, which significantly prolonged stent patency in animals.⁸ On the basis of these advances, the current research was undertaken to assess the safety and short-term clinical results of the airway bypass procedure using paclitaxel-eluting stents. It evaluates the applicability of the procedure to a multicenter study while suggesting an optimum target group for future clinical studies.

	Patients and Methods

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Patients with emphysema were enrolled in the study according to the following major criteria: computed tomographic scan evidence of bilateral emphysema; post-bronchodilator residual volume (RV) 220% or more of predicted; post-bronchodilator total lung capacity (TLC) 133% or more of predicted; post-bronchodilator FEV₁ 40% or less of predicted or FEV₁ of less than1 L; dyspnea scoring of 2 or more according to the modified Medical Research Council (mMRC) scale; arterial oxygen tension of 45 mm Hg or more on room air; and subjects who signed an informed consent form, were compliant, judged not suitable for other interventions, and considered fit to undergo a procedure under general anesthesia. Major exclusion criteria were the following: inability to walk more than 140 m at level in 6 minutes after pulmonary rehabilitation; presence of pulmonary hypertension (peak systolic pressure of >45 mm Hg or mean pressure of >35 mm Hg) as documented by 2-dimensional echocardiogram or right heart catheterization; any previous pulmonary resection; coronary artery disease with angina; history of myocardial infarction within 6 months or stroke less than 1 year before the procedure; insulin-dependent diabetes; unequivocal lung cancer or the presence of suspicious pulmonary nodule/infiltrate; large bullae; ventilator dependence; alpha-1 antitrypsin deficiency; coagulation disorder; steroid therapy of 20 mg prednisone or more per day; unequivocal and symptomatic bronchiectasis; and 3 or more respiratory infections requiring hospitalization within the past 12 months. Subjects who met the criteria underwent a pulmonary rehabilitation program of 16 to 20 sessions over 6 to 10 weeks, ending no greater than 6 weeks before the procedure. Rehabilitation resumed after the procedure for up to 8 weeks and was then encouraged but not required. Within 24 to 48 hours before the procedure, all subjects underwent a chest computed tomographic scan, spirometry, body plethysmography, and dyspnea scoring (baseline measurements). Subjects received intravenous antibiotics starting on arrival at the operating room. The airway bypass procedure was performed with the patient under general anesthesia with orotracheal intubation and controlled mechanical ventilation. The Exhale Emphysema Treatment System (Broncus Technologies, Inc, Mountain View, Calif) has 4 components: (1) the Exhale Doppler Probe, which is a catheter with a 1.4-mm ultrasonic Doppler transducer at the distal tip; (2) the Exhale Doppler Processing Unit, which amplifies the sounds of the Doppler probe; (3) the Exhale Transbronchial Dilation Needle, which is a combination 25-gauge needle and 2.5-mm dilation balloon catheter for passage creation and dilation; and (4) the Exhale Drug-Eluting Stent (3.3-mm inner diameter, 5.3-mm outer diameter, 2 mm in length) with paclitaxel embedded within the silicone layer mounted on a delivery balloon catheter (Figure 1). All these catheters were designed to pass through the 2 mm or larger working channel of a flexible bronchoscope. The system uses a standard, commercially available inflation syringe to inflate the balloons on the balloon catheters. Airway bypass was performed in a single session with a flexible bronchoscope. Efforts were made to place a minimum of 2 stents in each upper and lower lobe bilaterally. The middle lobe was not treated. Creation of each stented passage required 3 steps: (1) identification of a blood vessel–free location with a Doppler probe at the level of segmental bronchi; (2) fenestration of the bronchial wall using the transbronchial needle and dilating balloon; and (3) placement of a paclitaxel-eluting stent to hold the passage open. After stent placement, the subject was allowed to recover from anesthesia, a routine chest radiograph was performed in the recovery room, and the subject was returned to the hospital room the same day. Intravenous antibiotics were continued for the first 24 hours after the procedure until discharge from the hospital, when they were switched to an oral route for 7 consecutive days. Follow-up visits were scheduled for 30, 60, 90, 135, and 180 days after the procedure. Parameters measured were RV, TLC, forced vital capacity (FVC), and FEV₁. Key functional measurements were mMRC, 6-minute walk (6MW), and St George’s Respiratory Questionnaire (SGRQ). Safety was assessed through the solicitation of adverse event reports. Safety stopping rules included the following: 3% procedure-related death; 30% postprocedure pneumothorax requiring chest tube drainage for more than 7 days; 3% pulmonary bleeding requiring transfusion; and 15% worsened ventilatory status resulting in the need for mechanical ventilation.

View larger version (111K): [in this window] [in a new window]   Figure 1. Devices used for airway bypass: A, Exhale Doppler Probe; B, Exhale Transbronchial Balloon Dilation Needle; C, Exhale Drug-Eluting Stent mounted on delivery catheter; D, Exhale Drug-Eluting Stent deployed.

	Statistical Analysis

Top Abstract Introduction Patients and Methods Statistical Analysis Results Discussion References

	Results

Top Abstract Introduction Patients and Methods Statistical Analysis Results Discussion References

 
A total of 35 subjects at 7 centers completed the airway bypass procedure between July 2004 and October 2005. There were 19 men and 16 women with ages between 45 to 81 years (average 62 years). The majority of subjects (33/35; 94%) had homogeneous emphysema. A total of 264 stents were implanted successfully (median of 8 stents per subject, with a range of 2 to 12 stents). Three additional subjects were selected for, but did not complete, the procedure. One subject did not have stents implanted due to the abundance of blood vessels adjacent to the airway walls as detected by Doppler. In another subject the thickness of the airways prevented stents from being implanted. One death occurred after intraoperative bleeding during treatment (2.6% of all subjects; 0.4% of all passages made). At the time, this triggered the safety stopping rules for the study. The study was resumed after an extensive Data and Safety Monitoring Board investigation, which generated several modifications. Mean baseline versus 1-month and 6-month follow-up measurements are listed in Table 1. The mean values for all measurements listed showed statistically significant improvement between baseline and 1-month follow-up. At 6 months there was a statistically significant reduction in RV (–400 mL; P = .04) and dyspnea (–0.5; P = .025).

View larger version (137K): [in this window] [in a new window]   Figure 2. Image of an implanted stent at 6-month follow-up fiberoptic bronchoscopic examination.

	Discussion

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There is strong evidence from the results (Table 1) that the mechanism of action by which airway bypass works is a reduction in hyperinflation, measured by a reduction in lung volumes including RV and TLC. The average pretreatment RV in this study population was 5.34 L (257% of predicted normal), which illustrates the severity of gas trapping present in these subjects. Given that the procedure relies on the abundant collateral ventilation found in severely emphysematous lungs, airway bypass would be expected to reduce gas trapping the most in patients with extensive hyperinflation. A statistically significant reduction in hyperinflation, as reflected by RV, was observed throughout the 6-month follow up. This paralleled improvement in dyspnea. However, exercise capacity improvement, as measured by 6MW, was not sustained at 6 months. The cessation of the initial exercise capacity improvement might be due at least in part to the cessation of the perioperative rehabilitation program at 8 weeks. The benefits of rehabilitation before treatment were described in a report from the NETT, which demonstrated its effectiveness in preparing and selecting subjects for lung volume reduction surgery.¹⁵ We therefore hypothesized that the use of rehabilitation for all subjects selected for airway bypass would be beneficial, inasmuch as their muscular reconditioning is improved by the program, and which in turn allows further improvement in their overall condition, enhancing the benefit received from reducing hyperinflation by the airway bypass procedure.

The air flow measurement FEV₁ has been used as a standard outcome measure in both the NETT¹⁰ and in bronchoscopic lung volume reduction⁸ studies. However, the lack of significant change in FEV₁ after airway bypass, in the presence of significantly improved dyspnea and RV reduction in this study, suggests the effect produced by airway bypass is not reflected in the rapid exhalation as measured by FEV₁, but in reduced gas trapping as measured by RV. Indeed, FEV₁ has not been found to correlate with patient-centered outcomes such as exercise tolerance, dyspnea, or health-related quality of life, as opposed to hyperinflation, which is directly associated with dyspnea and exercise limitation.¹⁶ Studies with short- and long-acting bronchodilators have shown that substantial reduction in hyperinflation in patients with COPD may be followed by rather small changes in FEV₁.¹⁷ A recent study involving endobronchial valves for emphysema also has failed to demonstrate significant changes in FEV₁.¹⁸ The reduction in hyperinflation has been shown to correlate better with exercise endurance and dyspnea ratings than with spirometry parameters.¹⁹ The reduction of benefit observed between 1 and 6 months after the airway bypass procedure could be due to one or more factors, which include patient selection criteria, suboptimal selection of sites for stent placement, stent patency, or other yet-to-be-determined factors. Inasmuch as airway bypass relies primarily on abundant collateral ventilation, which is greatly enhanced in patients with severe emphysema, subjects with severely hyperinflated lungs are, theoretically, the most likely to benefit from the procedure. Retrospective analysis of our patients using RV/TLC ratios above and below median (Tables 2 and 3) suggests that the degree of pretreatment hyperinflation may be an important factor in indicating patients who are most likely to achieve long-term benefits. Analogous to other interventions for emphysema, the degree of chest remodeling and diaphragmatic motion can also play a role in the assessment of outcome, and studies are currently being carried out to investigate new methods. On the basis of these early results, we can anticipate that the target population for future studies and clinical application of this procedure will have to include patients with severe hyperinflation.

The ideal number and location of stents to place is yet to be determined. Initial attempts to implant approximately 10 stents were based on the study of excised human lungs.⁶ Analysis of the current data shows no correlation between the number of stents placed and the degree of improvement in RV at any time point. The ideal number and location of stent placement remains a focus of ongoing studies.

Analysis of the limited bronchoscopic evaluation at 6 months shows that paclitaxel-eluting stents seem to be associated with extended stent patency. These clinical results were consistent with the work reported by Choong and associates,¹⁴ which showed that 65% of paclitaxel-eluting stents in animals were patent at 12 weeks. Stent patency also remains a focus of ongoing studies. New approaches to mapping and computed tomographic evaluation of the stents may facilitate this work.

The major intraoperative risks involved in airway bypass include pneumothorax and airway bleeding. No instances of pneumothorax occurred and all but one bleeding episode was controlled locally with instillation of cold saline and epinephrine solution. The major bleeding episode that resulted in the subject’s death was attributable to stent placement away from the original "quiet spot" identified by the Doppler probe. An extensive investigation conducted by the study’s Data and Safety Monitoring Board, including a video review of the procedure regarding this event, resulted in several recommendations. Modifications incorporated into the study included a stand-by balloon blocker placed into the main bronchus during every procedure and the repeat Doppler scanning of the passages created and dilated by the needle–balloon device before deploying the stent.

The present study was designed to demonstrate the applicability of airway bypass to a multicenter study and proof of concept of the airway bypass procedure using the paclitaxel-eluting stent in subjects with moderate-to-severe emphysema. The subjects in this study had more severe disease (greater RV and TLC, shorter 6MW, less quality of life, and a higher percentage of homogeneous emphysema, 94% vs 46%, respectively) than those in the NETT. By retrospective analysis, the most statistically significant results were observed in patients with the greatest degree of pretreatment hyperinflation.

In conclusion, early results of the airway bypass procedure using a paclitaxel-eluting stent in a multicenter study have been shown to reduce hyperinflation and dyspnea and to improve pulmonary function in subjects with severe emphysema, especially in those with severe hyperinflation. The clinical improvements demonstrated in these preliminary clinical results support further investigation of the airway bypass procedure. Questions about patient selection, the optimal placement of the stents, and stent patency provide direction for further study.

	Acknowledgments

 
We acknowledge Joel D. Cooper, MD, Julia S. Rasor, MS, and Terese Bogucki for analysis and peer review of this manuscript, Peter Macklem, MD, Bonnie Stearns, and Corey Powell for the statistical analysis, the Broncus staff, and Broncus Technologies for sponsoring this study and for providing the equipment and technical support.

	Footnotes

 
Research supported by Broncus Technologies, Inc. Mountain View, Calif.

	References

Top Abstract Introduction Patients and Methods Statistical Analysis Results Discussion References

 

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This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Add to Personal Folders Download to citation manager Author home page(s): Paulo F.G. Cardoso Georgios Stamatis Permission Requests Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Cardoso, P. F.G. Articles by Eng, P. Search for Related Content PubMed Articles by Cardoso, P. F.G. Articles by Eng, P. Related Collections Trachea and bronchi Related Article