Self-Expanding Nitinol Stent Implantation for Treatment of Aortic Coarctation

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1 224 J ENDOVASC THER CLINICAL INVESTIGATION Self-Expanding Nitinol Stent Implantation for Treatment of Aortic Coarctation Ali-Mohammad Haji-Zeinali, MD 1 *; Payam Ghazi, MD 2 *; and Mohammad Alidoosti, MD 1 1 Department of Interventional Cardiology and the 2 Research Unit, Tehran Heart Center, Tehran University of Medical Sciences, Tehran, Iran. Purpose: To prospectively assess the efficacy of self-expanding nitinol aortic stents in the treatment of coarctation of the aorta (CoA). Methods: Between July 2005 and July 2008, 21 patients (14 men; mean age years, range 11 34) with CoA were treated with self-expanding Sinus-Aorta stents. The predilation balloon was selected to be,5 times the stenosis diameter. The stent diameter was selected to be 20% to 30% greater than the diameter of the undiseased aorta at the level of the diaphragm. Results: All procedures were successfully performed without any major complications. Predilation (mean balloon diameter 12.3 mm) and postdilation (mean balloon diameter 15.4 mm) were performed in 12 and 14 procedures, respectively. The mean diameter of the stents was mm (range 18 26). The mean peak transcoarctation pressure gradient decreased from mmhg (range ) before the procedure to mmhg (range 0 7; p,0.001). Cephalad stent dislodgement with the first-generation device occurred in 3 of 12 patients; 2 were treated with a second stent overlapping the first, and the third received 3 overlapped stents after the second stent migrated distally. No stent dislodgement occurred in the subsequent 9 patients treated with longer second-generation stents with anti-jump markers. None of the patients had dissection, arterial rupture, or other complications. On follow-up, 1 (5%) patient had recoarctation and minor stent migration after 18 months; another stent was deployed successfully. No evidence of aneurysm formation was seen in 7 patients undergoing arch imaging. Conclusion: CoA can be successfully and safely managed with self-expanding nitinol aortic stents without aortic wall complications. Stent malpositioning can be overcome using oversized stents with anti-jump markers. J Endovasc Ther. Key words: aorta, coarctation, coarctoplasty, nitinol stent, self-expanding stent, Sinus- Aorta stent Balloon dilation is an accepted intervention for treatment of coarctation of the aorta (CoA), 1 4 but this intervention may have suboptimal results due to vessel recoil, especially in patients with isthmus hypoplasia. 1,2 Moreover, recoarctation and aneurysm formation occur at significant rates in the long term. 1,2 Balloon-expandable stents were subsequently developed to overcome the limita- Presented as a poster the 2008 Congenital & Structural Interventions Congress, held in Frankfurt, Germany, on June 25 28, * Ali-Mohammad Haji-Zeinali and Payam Ghazi contributed equally to this project. The authors have no commercial, proprietary, or financial interest in any products or companies described in this article. Address for correspondence and reprints: Ali-Mohammad Haji-Zeinali, MD, Assistant Professor of Interventional Cardiology, Department of Interventional Cardiology, Tehran Heart Center, North Kargar and Jalal-Al-Ahmad Cross, Tehran, Iran. ali_zeinali_cardio@yahoo.com ß 2009 by the INTERNATIONAL SOCIETY OF ENDOVASCULAR SPECIALISTS Available at

2 J ENDOVASC THER SELF-EXPANDING STENTS IN AORTIC COARCTATION 225 tions of balloon aortoplasty 5 18 ; however, aneurysm formation persisted, with the added problems of stent fracture and dislodgement. 12,13,19,20 In a multi-institutional experience using balloon-expandable stents, Forbes et al. 21 observed a high incidence (14.3%) of acute complications, including aortic dissection, intimal tears, stent migration, and balloon rupture in the early years of the study. A few investigators have assessed the efficacy of self-expanding nitinol stents in a variety of locations, and some have shown them to be accurately implanted across an aortic coarctation and well apposed to the wall Moreover, they reported fewer acute aortic wall complications, as well as beneficial late remodeling on followup Considering the paucity of information that is available on the efficacy of the selfexpanding nitinol aortic stents in the treatment of CoA, we report our experience in patients with native or recurrent CoA and offer this approach as an alternative to the use of balloon-expandable stents. Study Design METHODS Under a protocol approved by the ethics committee of our institution, a prospective study was conducted between July 2005 and July 2008 with the goal of examining the safety and efficacy of the Sinus-Aorta selfexpanding nitinol stent (OptiMed Medizinische Instrumente GmbH, Ettlingen, Germany) for treatment of CoA in adolescents and adults. Inclusion criteria were age $10 years, weight $35 kg, a transcoarctation pressure gradient (TPG).20 mmhg, and a willingness to participate. The only exclusion criterion was the presence of unfavorable anatomy (such as severe hypoplasia of the proximal CoA or proximity of the CoA to the left subclavian artery) that would preclude balloon dilation and stent placement. The study stent, which has a closed-cell design for maximal radial force, is available in 2-mm increments over an expansion range of 14 to 28 mm; lengths range from 30 to 100 mm in 10-mm increments. There are 4 rounded tantalum markers on each end of the stent. The 100-cm-long delivery system, which is designed to track over and inch guidewires, has a 10-F outer diameter for stents with 14- to 16-mm diameters and 12-F for stents with diameters $18 mm. The application device has a braided outer sheath for high kink resistance and extreme flexibility for perfect steering. Moreover, it has radiopaque markers on the inner sheath for exact stent placement. A newer generation design with anti-jump technology was introduced during the study period. Procedure and Follow-up Patients were treated with 325 mg of aspirin from 2 days before the procedure. 22 After obtaining written informed consent, all patients underwent retrograde femoral artery catheterization under local anesthesia by Seldinger technique. They were given 5000 units of heparin during the procedure. The coarctation segment was crossed with a flexible-tip inch guidewire; a pigtail catheter was then passed over the wire into the arch. After measuring hemodynamic parameters, a descending aortogram was performed in the left anterior oblique or lateral view to delineate the coarctation segment. Measurements were taken of the coarctation, aortic isthmus, and the descending thoracic aorta below the coarctation and at the level of the diaphragm. In patients with severe coarctation, graded dilatations with progressively larger balloons were performed. The diameter of the predilation balloon was selected based on the CoA anatomy; the maximum balloon diameter did not exceed 5 times the diameter of the stenosed segment. The diameter of the stent was selected to be 20% to 30% greater than the diameter of the normal aorta at the level of diaphragm or the origin of the left subclavian artery. The stent length was optimized so that the stenosed segment was in the middle of the device and placement could be completed with no jumping. In patients with associated isthmic hypoplasia, the length was adjusted to allow good coverage of the isthmus. The delivery system was introduced retrogradely

3 226 SELF-EXPANDING STENTS IN AORTIC COARCTATION J ENDOVASC THER through a 12-F transfemoral introducer sheath over the extra-stiff guidewire. After positioning the stent across the target site, the exact position was confirmed with the help of body markers. Keeping the delivery system straight, the stent was deployed as the outer sheath was withdrawn by manipulating the trigger on the delivery system. After deployment, balloon postdilation was performed in patients with a pressure gradient.5 mmhg. At its maximum, the balloon diameter was equal to that of the descending thoracic aorta at the level of the diaphragm. Angiography was repeated; when the heart rate reached near the pre-angioplasty rate, the pressure was recorded across the stented segment. No heparin or anticoagulation was given after completion of the procedure. Aspirin (80 mg/ d) was prescribed for 6 months. 22 Follow-up was performed at 1 and 6 months after the procedure and then at 6- month intervals. Follow-up included assessment of blood pressure in all extremities, recording the antihypertensive medications, chest radiography, and echocardiography. Computed tomographic angiography (CTA) was performed occasionally for optimal assessment of the aortic arch. Improvement in hypertension was based on the resting systolic blood pressure in the right arm. Cardiac catheterization was repeated to investigate possible recurrence if the peak TPG on echocardiography was.20 mmhg. Recoarctation was diagnosed based on an angiographic TPG.20 mmhg at catheterization. Patient Population During the study period, 21 consecutive patients (14 men; mean age years, range 11 34) were enrolled (Table). The majority (n519) had de novo coarctation (15 discrete and 4 with associated isthmic hypoplasia); 2 had postsurgical recoarctation. Mean baseline systolic blood pressures proximal and distal to the CoA before the procedure were and mmhg, respectively. The mean diameters of the aortic arch, the aorta above and below the coarctation, and the aorta at the level of diaphragm were , , , and mm, respectively. TABLE Characteristics of 21 Aortic Coarctation Patients Men/women 14/7 Age, y (11 34) Weight, kg (36 87) Body mass index, kg/m ( ) Hypertension 17 (81%) Systemic blood pressure, mmhg Antihypertensive therapy 17 (81%) Mono therapy 6 Multi therapy 11 Associated cardiac defects 14 (67%) Bicuspid aortic valve 12 Isthmus/arch hypoplasia 4 Aortic stenosis 2 Subaortic stenosis 1 Aortic regurgitation 7 Tricuspid regurgitation 3 Mitral regurgitation 7 Atrial septal defect 1 Continuous data are presented as means 6 standard deviation; categorical data are given as counts (percentages). Statistical Analysis Data are presented as the mean 6 SD. Comparison of individual parameters was performed using the paired Student t test and Wilcoxon signed rank test as appropriate. P,0.05 was considered statistically significant. RESULTS Predilation was performed in 12 (57%) of 21 procedures using balloons ranging from 7 to 155 mm in a diameter (mean mm). The study stents (mean mm diameter, range 18 26) were successfully implanted in all patients (Fig. 1). In the initial 12 patients, shorter first-generation stents were deployed; the following 9 patients received longer ($60 mm) second-generation Sinus-Aorta stents with anti-jump markers. Postdilation was done in 14 (67%) procedures with balloons averaging mm in diameter (range 12 20). The mean peak TPG decreased from mmhg (range ) before the procedure to mmhg (range 0 7; p,0.001) after stent implantation. The mean diameter of the stenosed area increased from mm to mm after stent de-

4 J ENDOVASC THER SELF-EXPANDING STENTS IN AORTIC COARCTATION 227 Figure 1 Serial aortograms in left anterior oblique projection depicting (A) severe native coarctation of the aorta before angioplasty, (B) predilation angioplasty with a mm balloon, (C) implantation of a mm self-expanding nitinol Sinus-Aorta stent, and (D) postdilation angioplasty using an mm balloon. (E) Significant increase in isthmus diameter from 3 to 18 mm is seen after stent placement, with a more flared lower stent segment attached to the dilated aortic wall. ployment (p,0.001). Systolic blood pressures proximal and distal to the CoA showed significant improvement to and (both p,0.001 versus baseline), respectively. Cardiac surgery for aortic valve replacement was performed in 3 patients after the CoA treatment. Complications Acute stent dislodgements (3 proximal jumps, 1 distal migration) requiring additional stent deployment occurred in 3 patients. Two cases were treated by implanting a second stent. In the third patient, the second stent migrated distally after the first one had jumped proximally; a third stent was deployed to overlap the others at either end. These events arose in the initial 12 patients who had been treated using first-generation Sinus-Aorta stents; it did not happen after the second-generation stents with anti-jump markers became available (n59 cases). No patient had dissection, arterial rupture, acute or subacute thrombus formation, or any evidence of distal embolization. Follow-up All patients were followed for months (median 14, range 1 30). None of the patients showed evidence of stent fracture on chest radiographs. All the patients are asymptomatic. Systolic blood pressure remained consistently lower ( mmhg before stent placement to mmhg at follow-up; p,0.001). Before stent therapy, 17 (81%) patients were hypertensive and 11

5 228 SELF-EXPANDING STENTS IN AORTIC COARCTATION J ENDOVASC THER Figure 2 Serial aortograms in left oblique view in a 17-year-old patient at 18-month followup demonstrating (A) mild stent migration resulting in a recurrent TPG of 35 mmhg, (B) implantation of a second Sinus-Aorta stent overlapped with the previously placed stent across the coarctation segment, (C) postdilation balloon angioplasty, and (D) no residual stenosis after stent deployment. (52%) received.1 antihypertensive drug (multi therapy); at follow-up, only 3 (14%) remained on multi therapy. Doppler echocardiography in 18 patients identified one with a pressure gradient of 40 mmhg 18 months after his initial stent implantation. Angiography confirmed a recurrent gradient of 35 mmhg, with minor stent migration. He was successfully treated using another self-expanding stent overlapped with the previous one; the gradient was reduced to 5 mmhg (Fig. 2). Another patient with a gradient of 25 mmhg on echocardiography 30 months after stent implantation underwent repeat cardiac catheterization, which found only a 15 mmhg gradient across the stent. The patient was discharged without any additional intervention. In the 16 remaining patients, the mean Doppler gradient was mmhg (range 0 15) at follow-up. Three patients did not have echo but were followed clinically. None of the patients had aneurysm formation according to echocardiography. Of 21 patients, 7 underwent CT angiography at a median of months (range 21 32); none had abnormal findings of aneurysm formation, dissection, or in-stent restenosis. DISCUSSION Most studies to date have used different types of balloon-expandable stents such Palmaz, Genesis XD, Cheatham-Platinum, or covered NuMED stents for the endovascular management of CoA Balloon-expandable stent placement has remained a technically demanding procedure associated with a high incidence of clinical aortic wall complications, although the technical complications significantly declined after January 2002 in one cohort. 21 On the other hand, self-expanding nitinol aortic stents, which are flexible, have no welding spots, and are easy to deploy, have been accurately implanted in a few cases of CoA. 22,23 Hence, we hypothesised that the use of self-expanding stents could give similar results with fewer clinical aortic wall complications compared with balloonexpandable stents. However, considering that the OptiMed stents had not been used in our country before, we had concerns over technical complications (dislodgement and adequate radial force). Our initial experience with stent treatment for CoA suggested that proper stent sizing plays an important role in the management of this pathology. When using balloon-expandable stents, the diameter is chosen to equal that of the normal portion of the transverse arch or proximal isthmus at the level of the left subclavian artery but not greater than the diameter of the descending thoracic aorta at the level of the diaphragm. 12,13 Considering that there are different types of coarctation, each of which may have thoracic aortic dilatation either proximal or distal to the isthmus, the stent size may be disproportional to the proximal or distal aortic segments. If the stent size is smaller than the segment

6 J ENDOVASC THER SELF-EXPANDING STENTS IN AORTIC COARCTATION 229 distal to the coarctation site, the stent may be malapposed, which may lead to stent migration due to the force of forward blood flow and aortic wall pulsation. If the stent is larger than the outflow segment, overdilation of the stenosed segment may result in dissection or rupture of the aorta. These complications have always been an important concern to us during deployment of balloon-expandable stents, so very careful attention must be paid to the appropriate sizing of balloon-expandable stents. In this series, we oversized the self-expanding stent diameters by,20% to 30% more than the aortic diameter at the level of the diaphragm or a normal portion of the transverse arch. Even though the risk of severe injury leading to dissection or rupture of the aorta may increase due to the use of a largerdiameter balloon-expandable stent, our experience suggests that the oversized self-expanding models are not able to overdilate the stenosed segment because of lower radial strength. Thus, oversizing the stent diameter was not a concern for us. Many stents that are sized to fit in the aorta proximal to the lesion hang into the dilated poststenotic region without making significant contact with the vessel wall. Thus, if we observed a dilated thoracic aorta downstream of the lesion, the stent diameter was 30% greater than the diameter at the level of the diaphragm or normal portion of the transverse arch for proper apposition in the poststenotic area. For example, if a patient had aortic diameters of 18 and 23 mm at the diaphragm and the poststenotic segment, respectively, we selected a 24-mm stent (Fig. 1). Based on our experience, the isthmus typically was not properly opened without postdilation. In this region, the balloon was sized to equal that of the descending thoracic aorta at the level of the diaphragm (18 mm in the example above). With this approach, the upper and lower parts of the stent were more flared and better apposed to the dilated aortic wall, while in the mid-stent isthmus region, the stent was dilated to match the diameter at the level of the diaphragm. This coverage of the coarctation area using oversized self-expanding stents may explain our low residual TPG compared to most of the other reports, 12 14,21,22 even though our study patients had more severe coarctation as evidenced by the higher grade of stenosis. In terms of coarctoplasty complications, there are 2 categories: aortic wall and technical sequelae. In the study by Hamdan et al., 12 6 (17%) of 34 patients treated with Palmaz balloon-expandable stents had complications. A retroperitoneal hematoma and embolization of a ruptured balloon fragment required surgical treatment; 3 stent migrations and 1 femoral arteriovenous fistula occurred as well. Harrison et al., 13 who also used Palmaz stents, reported 4 (14%) complications including 1 balloon rupture (surgical removal), 1 major stent migration (placement of 2 additional stents), 1 minor migration, and 1 cerebrovascular accident (CVA). In Forbes multi-institutional study 21 of different stent types [84% Palmaz and Genesis XD stents, 16% other stents like Cheatham- Platinum or DS/Mega/Maxi or covered NuMED stents], acute complications were encountered in 81 (14.3%) of 565 patients, comprising 22 aortic wall complications (8 intimal tears, 9 aortic dissections/ruptures, and 6 aortic aneurysms) and 64 technical complications (28 stent migrations, 13 balloon ruptures, 5 CVAs or peripheral embolizations, and 13 access site hematomas). Although there was not any significant relation between technical complications and stent type in this series, balloon rupture alone was associated significantly with the Palmaz stent (9/13 instances). In Tyagi s report, 22 self-expanding Memotherm nitinol aortic stents were deployed in 16 patients; they did not have any aortic wall and technical complications. In our study, we had a 14% rate of acute technical complications (3 stent dislodgements), all 3 events in the initial 12 patients. It seemed that the stenosed segment pushed the stent forward, particularly when we did not have effective predilation. If the dislodgement was too great, the stent did not completely cover the stenosis, requiring a second stent. This problem was solved with the introduction of the second-generation stent delivery systems with the proximal and distal anti-jump markers.

7 230 SELF-EXPANDING STENTS IN AORTIC COARCTATION J ENDOVASC THER In addition, we did not have any aortic wall complications. Considering that the self-expanding stents do not provide substantial radial strength and do not have sharp edges, they are less traumatic to the aortic wall and may decrease the probability of aortic rupture or dissection. This is consistent with other studies employing self-expanding stents On the other hand, the Palmaz stents are rigid, with sharp edges that can cause trauma or even rupture the delivery balloon and result in vascular injury as noted above. 12,13,21 Furthermore, aortic wall complications can result from the deployment of an oversized stent or rapid balloon inflation. In the literature, this complication increased significantly with aggressive predilation 21 and in patients with a weakened aortic wall due to old age or other diseases A review of the literature did not find any report of stent dislodgement associated with self-expanding stents, 22,24,25 whereas it has been considered as one of the major technical complications during deployment of balloonexpandable stents in many series. 10,12 14,16,21 In these studies, the most frequent causes for this complication have been balloon rupture during stent implantation, stent placement on an undersized balloon catheter (compared to the proximal aorta diameter), and an inadequate diameter or underexpansion of the stent. However, improvements in balloon catheters and stent technology and shorter learning curves have lowered the technical complication rate in recent years. 21 We saw this in our experience, as well, after introduction of the longer stents with anti-jump markers; the newer-generation device prevented the stent dislodgement we had seen with the earlier system. In follow-up, our single case of recurrence aroseinapatientwhohadisthmichypoplasia; in such cases, higher radial strength is required, and balloon-expandable stents may be more appropriate. 22 None of the 7 patients undergoing CTA had aneurysm formation or other complications, which is consistent with Tyagi s study 22 with the self-expanding Memotherm stents (16 patients). On the other hand, Forbes et al. 30 followed 144 of 588 procedures from 0.5 to 92 months with arch imaging; they reported 16 patients with neointimal hyperplasia, 13 with aneurysm formation, 6 with stent fracture (4 Cheatham-Platinum stents and 2 Genesis XD), and 5 dissections or intimal tears. In Harrison s report, 13 3 of 18 patients followed 0.1 to 3 years with cardiac catheterization had developed aneurysm. Limitations Although this study is one of the largest reported groups of CoA patients managed with the Sinus-Aorta self-expanding stent, the number of patients was small and follow-up was short compared to the expected lifespan of the patients. Moreover, we did not compare the study population to patients managed with balloon-expandable stents. A randomized comparison would be the optimal assessment, but it would require the involvement of multiple centers with expertise in both techniques to complete within a reasonable time. We used oversized stents and echocardiography to monitor stent performance; however, echo may be less sensitive compared to angiography, CT, or magnetic resonance imaging in detecting aneurysm or restenosis following stent deployment. 25,31 Thus, our observations regarding these complications would be strengthened by using a more sensitive imaging technique in the 14 patients who have had only echo follow-up thus far. Conclusion Coarctation and recoarctation of the aorta can be successfully and safely managed with self-expanding nitinol aortic stents with acceptable procedural risk, especially in terms of aortic wall complications. It appears that stent dislodgement during deployment can be overcome using longer stents with anti-jump markers. Current techniques used to size balloon-expandable stents for CoA treatment should be reevaluated/revised when using self-expanding nitinol aortic stents. Acknowledgment: Our special thanks go to Dr. Zahid Amin for carefully reviewing the manuscript. Moreover, the authors thank Ms. Leila Keivan-Mehr for assisting us with patient data acquisition.

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