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Early and late assessment of the Micro Stent PL coronary stent for restenosis and suboptimal balloon angioplasty
Interventional Cardiology
Early and late assessment of the Micro Stent PL coronary stent for restenosis and suboptimal balloon angioplasty J o h n G. Webb, MD, a J e f f r e y J. P o p m a , MD, b A l e x a n d e r J. L a n s k y , MD, b R o n a l d G. Carere, MD, a A l a n Rabinowitz, MD, a Joel Singer, Ph.D., a a n d A r t h u r Dodek, MD a Vancouver, British Columbia,
Canada, and Washington, D.C.
This prospective study represents the initial assessment of the Micro Stent PL (Arterial Vascular Engineering, Inc.) coronary stent. From one to three radiopaque stainless steel stents, each measuring 4 mm long, were premounted onto specially designed balloon catheters. A total of 123 stents were implanted in 41 patients without procedural failure or complications. Stent dislodgment proved a concern, with 7 of 123 stents (5.7%) moving >3 mm from the site of placement and late downstream migration occurring in an additional patient. Subacute stent thrombosis occurred in two patients (5%). Six-month angiographic follow-up was available in 37 of 41 patients (90%). Minimal lumen diameter at baseline was 0.93 ± 0.51 mm, increasing to 2.74 ± 0.49 mm after stenting, and falling to 1.66 ± 0.89 mm at 6 months; this represents a late loss of 60% of the initial gain. Restenosis, based on a binary definition of >50% diameter stenosis, was documented in 18 patients (49%). Advantages of the Micro Stent PL include its radiopacity and marked ease of distal delivery. The potential for stent dislodgment has implications for future stent designs. The role of the Micro Stent PL in managing restenosis is unclear, but it appears useful in the management of dissection and threatened closure after balloon angioplasty. (Am Heart J 1997;133:369-74.)
C o n s i d e r a b l e experience h a s b e e n g a i n e d w i t h t h e P a l m a z - S c h a t z stent, 1"3 t h e W a l l s t e n t , 4 t h e G i a n t u r c o - R o u b i n F l e x S t e n t , 5-7 a n d t h e W i k t o r stent. 8, 9 P r e l i m i n a r y a s s e s s m e n t of t h e Micro S t e n t P L (Arterial V a s c u l a r E n g i n e e r i n g Inc., S a n t a Rosa, Calif.) a n d its p r o t o t y p e device h a s b e e n reported. 1°, 11 We p r e s e n t t h e initial a n d late clinical a n d a n g i o g r a p h i c e v a l u a t i o n of t h e Micro S t e n t PL. From the aInterventional Cardiology Group, St. Paul's Hospital, University of British Columbia, and bWashington Hospital Center. Reprint requests: John G. Webb, MD, 502-1160 Burrard St., Vancouver, B.C., Canada V6Z 2E8. Copyright © 1997 by Mosby-Year Book, Inc. 0002-8703/97/$5.00 + 0 4/1/75871
METHODS Device description. The Micro Stent PL is constructed
of 316L stainless steel wire with a cross-sectional diameter of 0.008". A single circular strand is fashioned such that each stent has a total of eight longitudinal struts with four crowns at either end. Individual stents are 4 m m long with a nonexpanded profile of 0.065" (Fig. 1). Monorail or coaxial dual marker balloons measure 6, 10, and 15 m m long to accommodate one, two, or three stents, respectively. The compliant polyethylene balloon material is heat shrunk and slightly redundant to partially envelope the stent struts. Study protocol. Eligible patients had either restenosis or suboptimal results/threatened closure after balloon angioplasty and were able to give informed consent. The study protocol was approved by research review committees of St. Paul's Hospital, the University of British Columbia, and the Bureau of Medical Devices, Department of Health and Welfare, Canada. After 6 months of clinical follow-up, patients underwent coronary angiography. Stent procedure. Lesions were predilated with a standard angioplasty balloon. From one to three stents were deployed to just above the nominal pressure of 6 atm (mean 7.8 + 2.4 arm). During the study, high:pressure inflations, oversized balloons, and intravascular ultrasound were not routinely used, although all three modalities were used in selected patients. Patients were premedicated with aspirin. Heparin (10,000 units) was administered and the activated clotting time was maintained above 300 seconds. Dextran was begun during the procedure at a dosage of 50 ml/hour for a total of 1,000 ml. Sheaths were removed 4 hours after the procedure and heparin was reinstituted 4 hours later. Warfarin (international normalized ratio >2.5) was continued for 1 month and aspirin was continued indefinitely. Qualitative and quantitative angiographic outcomes.
Angiograms were analyzed by the Washington Hospital 369
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Fig. 1. Micro Stent PL. Left, Single and triple premounted, 4 mm long stents. Middle, Balloon expansion. Right, Three fully expanded stents. Angiographic Core Laboratory using standard qualitative morphologic and quantitative angiographic criteria.12 Two projections demonstrating the stenosis in its sharpest and tightest views were selected for quantitative analysis. Cineframes were magnified optically 2.0:1 to 2.5:1 and digitized into a 512 x 512 x 8-bit pixel matrix using a cinevideo converter and a CAP-35 mm (General Electric, Milwaukee, Wis.) interfaced to an 80406 computer that used Cardiovascular Measurement System analysis.12The image is calibrated with the contrast-filled catheter serving as the reference source. Minimal lesion diameter and interpolated reference diameter were used to calculate percent diameter stenosis. Statistical analysis. All data are expressed as the mean value -+ SD. Comparisons were performed using t tests for continuous variables and the chi-square test for dichotomous variables. A statistical probability ofp -< 0.05 was considered significant. RESULTS Study patients. Forty-one patients were enrolled between March 1994 and J a n u a r y 1995, with suboptimal results or threatened closure after balloon angioplasty in 20 patients and restenosis in 21. Mean age was 61 _+ 10 years, with 36 male patients (88%) and 10 diabetic patients (24%). Single-vessel disease was present in 22 (54%), double-vessel disease in 13 (32%), and triple-vessel disease in 6 (14%). Left ventricular ejection fraction was 65% _+ 11%. Twentyeight patients (68%) had a prior history of percutaneous transluminal coronary angioplasty (PTCA), 9
(22%) had had bypass surgery, and 24 (59%) had had infarction. Patients undergoing stent implantation for restenosis tended to be older t h a n patients with threatened closure (64 vs 57 years, p < 0.05) and were less likely to have coronary occlusion (Thrombolysis in Myocardial Infarction [TIMI] trial perfusion grade 0 or 1) before angioplasty (1 vs 5, p = 0.03). The stented artery was the left anterior descending artery in 18 patients (43%), the circumflex artery in 9 (21%), the right artery in 12 (29%), and a vein graft in 3 (7%). The lesion was ostial in 2 patients (5%), proximal in 17 (42%), midvessel in 18 (44%), distal in 2 (5%), and anastomotic in 2 (5%). TIMI grade <3 was noted in 9 patients (22%), thrombus in 6 (15%), eccentricity in 11 (27%), a bifurcation in 16 (39%), moderate or severe calcification in 9 (22%), and irregularity in 12 (29%). Average lesion angulation was 24 _+ 16 degrees, and average length was 10.2 _+ 0.5 mm. Procedural outcome..One hundred twenty-three stents were implanted in 44 coronary vessels. From one to eight stents (mean 2.8) were implanted per vessel. The initial deployment involved a single stent in 4 patients (9.5%), two stents in 24 (57%), and three stents in 14 (33%). A second deployment was used in 15 patients, with a single stent in 7 (17%), two stents in 8 (19%), and three stents in 2 (5%). Three patients required a third deployment.
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Fig. 2. A, Acute inferior infarction with right coronary occlusion. B, Initial balloon dilation is unsuccessful. C, A spiral dissection extends from proximal artery to beyond crux. D, Gianturco-Roubin FlexStent stent could only be advanced as far as midvessel. E, Palmaz-Schatz stent would not cross previously placed stent.
Fig. 3. A, Slow outflow and occlusion of posterior descending branch remains. B, Six Micro Stent PL devices were easily advanced through both previously placed stents and deployed in distal artery. C, The proximal Palmaz-Schatz stent is not visible (open arrow), the FlexStent is dimly seen (curved arrows), yet Micro Stent PL is easily seen (straight arrows). D, Artery remains patent at 4-month follow-up despite persistent visible dissection. All stenting procedures were successful. No difficulty was encountered passing the stent delivery system through a standard lumen rotating hemostatic valve or standard 8F (0.078" to 0.084" inter-
nal diameter) guiding catheters. Stents were easily visualized by fluoroscopy. Stents were easily delivered into distal vessels through tortuous anatomy and through previously placed stents (Figs. 2 and 3).
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Fig. 4 A, Previously totaled occluded saphenous vein graft remains patent 4 months after intracoronary thrombolysis and angioplasty. Residual anastomotic stenosis is present. B, Two stents are easily advanced across stenosis. C, Stents have slid slightly to either side of most severe stenosis, requiring placement of third stent. D, Third stent is easily advanced between two previously placed stents. E, Good stent placement is accomplished. F, Graft remained patent at 6-month angiographic follow-up.
Table I. Clinical outcome
Six-month follow-up
In hospital
~of
~of
No. of total No. of total Complications complications patients complications patients Death Cardiac surgery Infarction Stent occlusion Stent PTCA Vascular complications Any of the above
0 0 0 0 2 0
0 0 0 0 5 0
0 2 2 2 8 0
0 5 5 5 20 0
2
5
10
25
In our series, stenting over side branches did not impair flow and side branches were easily dilated in two patients with bifurcation lesions. In no case did a stent become dislodged from the
balloon catheter before planned deployment. However, in six patients (14%), significant (->3 mm) stent movement (7 of 123 stents, 5.7%) was documented after deployment at the initial procedure. Dislodgment occurred as a result of slippage on the shoulder of a bulky lesion (two stents) or at a bend point (one stent), at withdrawal of the deflated stent delivery balloon (two stents), or on recrossing with a previously inflated winged balloon (two stents). In another instance the most distal of three stents implanted in the proximal lefLanterior descending artery was found at 6-month follow-up to have migrated 10 mm downstream. In no case was stent dislodgment associated with complications other than the necessity of implanting additional stents (Fig. 4). Clinical o u t c o m e . In-hospital and follow-up (6 month) clinical outcome is presented in Table I. No patient required urgent coronary artery bypass, vascular repair, or transfusion, had a myocardial in-
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farction, or died. All patients were free of angina at discharge. At 6-month follow-up, 21 patients (52%) remained in Canadian Cardiovascular Society class 0 or 1, 5 (13%) in class 2, 8 (21%) in class 3, and 5 (13%) in class 4. At follow-up two patients (5%) had suffered a myocardial infarction, eight patients (20%) had undergone a second PTCA procedure, two patients (5%) had undergone elective coronary artery bypass, and two patients (5%) experienced stent occlusion. There were no deaths. Angiographic outcome. Postprocedural angiography documented thrombus in two patients (5%). Type A dissections (luminal haziness) remained in two patients (5%), type B (linear dissection) remained in 2 (5%), and type C (extraluminal contrast) remained in two (5%), with a mean dissection length of 3.4 _+ 2.0 mm. 12 Quantitative coronary angiographic outcomes are listed in Table II. Baseline minimal lumen diameter (MLD) was 0.93 _+ 0.51 mm and increased to 2.74 +_ 0.49 mm after stenting (p < 0.001). In the subgroup of patients with threatened closure, MLD increased from 1.95 _+ 0.77 mm after balloon angioplasty alone to 2.60 + 0.55 mm after stenting (p < 0.001). Follow-up angiography was available in 37 patients (90%). At follow-up MLD fell to 1.66 _+ 0.89 mm (p < 0.001), representing a late loss of 60% of the initial gain. As determined by CMS, the percent diameter stenosis before the initial procedure was 67% _+ 22%, after stenting it was 14% _+ 21%, and at follow-up it was 47% _+ 23%. Restenosis (using a binary definition of >50% diameter stenosis) was present in 49% of all lesions, 44% of restenotic lesions, and 56% of suboptimal angioplasty lesions. In patients with restenosis, intimal proliferation was often visible as a lucency separating the stent struts and opacified arterial lumen. Stent thrombosis. In-hospital stent thrombosis did not occur. Post hospital thrombotic stent occlusion occurred in two patients (5%) at 5 and 7 days. These two events accounted for the 5% incidence of late myocardial infarction in this series. In one patient aspirin and warfarin h a d been discontinued in error after stenting of a complex dissection and threatened closure. The second patient had a complex dissection tacked up by a single 4 mm stent. It was apparent that an insufficient length of the artery had been stented and additional stents were implanted. Both vessels remained patent at 6-month follow-up angiography. DISCUSSION
This experience demonstrates that the Micro Stent PL is associated with a favorable early outcome in
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Table I]. Quantitative angiographic results Measure Reference d i a m e t e r Baseline Final Follow-up Minimal l u m e n d i a m e t e r Baseline Final Follow-up D i a m e t e r stenosis Baseline Final Follow-up Stenosis ->50%
Result
3.19 _+ 0.50 m m 3.32 +- 0.57 m m 3.08 _+ 0.44 m m 0.93 _+ 0.51 m m 2.74 _+ 0.49 m m 1.66 _+ 0.89 m m 67% -+ 22% 14% -+ 21% 47% _+ 23% 18/37 (49%)
patients with prior restenosis or suboptimal balloon angioplasty. The short length of the stents allows the operator to match the number of stents to the length of the lesion and favors delivery through tortuous anatomy. Radiopacity allows accurate stent positioning and confirmation of deployment, while the relatively open design allows opacification of the arterial lumen within the stent confines despite the radiopacity of the stent struts. The potential for stent dislodgment is a limitation of this stent design. The longitudinal orientation of the smooth, nonoverlapping stent struts favors easy advancement, but it may not always securely adhere to the arterial wall. We recommend slight oversizing of the Micro Stent PL, waiting for full balloon deflation before withdrawing the delivery balloon under fluoroscopy. Furthermore, recrossing a recently deployed stent should be avoided if possible. Clinical outcomes compare favorably with those reported in other series of coronary stenting, 1-9 with no infarction, emergency surgery, or mortality in this relatively high-risk group. Subacute stent thrombosis did occur in two patients in whom stents were implanted for threatened closure, a condition that may predispose to stent thrombosisfl 5-7, 13 This 5% incidence of stent thrombosis (95% confidence interval 0% to 12%) compares favorably with other early reports of bailout stenting of 3.5% to 8% with the Palmaz-Schatz stent,1, 13, 147% with the FlexStent, 5-7 and 17% with the Wiktor stent, s Vascular complications were notably absent in this study, despite the aggressive anticoagulation required by the study protocol. A binary restenosis rate of 49% (95% confidence intervals 33% to 65%) seems high when compared with other stent series. 2-4, 14 This may reflect a study population composed of patients at high risk of restenosis, including those with prior restenosis, 15
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suboptimal balloon angioplasty, 16 and recanalized total occlusions. 17, is In vitro testing has determined that, for an average vessel of 3.5 mm, the expanded Micro Stent PL will cover 8.4% of the luminal surface area. Although speculative, a low surface area and relatively deep penetration into the arterial wall may adversely affect the arterial response to stenting. This study of necessity represents a learning curve, and patient numbers prohibit direct comparison of event rates with other stents. The study protocol was designed at a time when anticoagnlation protocols were more aggressive than are currently thought necessary and was performed before recent trends in stenting techniques such as high-pressure balloon inflation and oversizing. 19 In conclusion, the advantages of the Micro Stent PL include its ease of distal delivery through tortuous anatomy, its radiopacity, and t h e ability to incrementally stent lesions of varying length. Caution is required due to the potential for stent dislodgment. Future articulated modifications of this basic stent design (the Micro Stent) have been developed on the basis of this experience and appear likely to reduce this concern. The role of this stent in managing restenosis is unclear. However, the Micro Stent PL appears useful in managing suboptimal results and threatened closure after balloon angioplasty. REFERENCES
1. George BS, Voorhees WD III, Roubin GS, Fearnot NE, Pinkerton CA, Raizner RE, et al. Multicenter investigation of coronary stenting to treat acute or threatened closure after percutaneous transluminal coronary angioplasty: clinical and angiographic outcomes. J Am Coll Cardiol 1993;22:135-43. 2. Fischman DL, Leon MB, Baim DS, Schatz RA, Savage MP, Penn I, et al. A randomized comparison of coronary stent placement and balloon angioplasty in the treatment of coronary artery disease. N Engl J Med 1994;331:496-501. 3. Serruys PW, de Jaegere P, Kiemeneij F, Macaya C, Rutsch W, Heyndrickx G, et al. A comparison of balloon-expandable stent implantation with balloon angioplasty in patients with coronary artery disease: Benestent Study Group. N Engl J Med 1994;331:489-95.
American Heart Journal
4. Serruys PW, Strauss BH, Beatt KJ, Bertrand ME, Puel J, Rickards AF, et al. Angiographic follow-up after placement of a self-expanding coronary stent. N Engl J Med 1991;324:13-7. 5. Nath FC, Muller DWM, Ellis SG, Rosenschein U, Chapekis A, Quain L, et al. Thrombosisof a flexible coil coronary stent: frequency, predictors and clinical outcome. J Am Coll Cardiol 1993;21:622-7. 6. Sutton JM, Ellis SG, Roubin GS, Pinkerton CA, King SB III, Raizner AE, et al. Major clinical events after coronary stenting: the multicenter registry of acute and elective FlexStent stent placement. Circulation 1994;89:1126-37. 7. Agrawal SK, Ho DS, Liu MW, Iyerr S, Heam JA, Cannon AD, et al. Predictors of thrombotic complications after placement of the flexible coil stent. Am J Cardiol 1994;73:1216-9. 8. Vrolix M, Piessens J. Usefulness of the Wiktor stent for treatment of threatened or acute closure complicating coronary angioplasty: the European Wiktor Stent Study Group. Am J Cardiol 1994;73:73741. 9. White CJ, Ramee SR, Collins TJ. Elective placement of the Wiktor stent after coronary angioplasty. Am J Cardiol 1994;74:274-6. 10. Webb J, Stertzer S, Ahmad T, Carere R, Mercier B, Dodek A. Multicenter clinical experience with the development of a novel short coronary stent and its prototype device. Cathet Cardiovasc Diagn 1996;37:120-4. 11. Ozaki Y, Keane D, Ruygrok P, De Feyter P, Stertzer S, Serruys PW. Acute clinical and angiographic results with the new AVE Micro coronary stent in bailout management. Am J Cardiol 1995;76:112-6. 12. Popma JJ, Bashore TM. Qualitative and quantitative angiography. In: Topol E J, editor. Textbook ofinterventional cardiology. Baltimore: WB Saunders, 1994:1052-68. 13. Metz D, Urban P, Hoang V, Canemzind E, Chatelain P, Meier B. Predicting ischemic complications after bailout stenting following failed balloon angioplasty. Am J Cardiol 1994;74:271-4. 14. Schomig A, Kastrati A, Dietz R, Rauch B, Neumann FJ, Katus HH, et al. Emergency coronary stenting for dissection during percutaneous transluminal coronary angioplasty: angiographic follow-up aftsr stenting and after repeat angioplasty of the stented segment. J Am Cell Cardiol 1994;23:1053-60. 15. Moscucci M, Piana RN, Kuntz RE, Kugelmass AD, Carrozza JP, Senerchia C, et al. Effect of prior coronary restenosis on the risk of subsequent restenosis after stent placement or directional atherectomy. Am J Cardiol 1994;73:1147-53. 16. Kuntz RE, Gibson CM, Nobuyoshi M, Bairn DS. Generalized model of restenosis after conventional balloon angioplasty, stenting, and directional atherectomy. J Am Cell Cardiol 1993;21:15-25. 17. Ivanhoe RJ, Weintraub WS, Douglas JS Jr, Lembo LJ, Furman M, Gershony G, et al. Percutaneous translumir al coronary angioplasty of chronic total occlusions: primary success, restenosis, and long-term follow-up. Circulation 1992;85:106-15. 18. Bell MR, Berger PB, Bresnahan JF, Reeder GS, Bailer KR, Holmes DR. Initial and long-term outcome of 354 patients after coronary balloon angioplasty of total coronary artery occlusions. Circulation 1992;85: 1003-11. 19. Columbo A, Hall P, Nakamura S, Almagor Y, Maiello L, Martini G, et al. Intracoronary stenting without anticoagulation accomplished with intravascular ultrasound guidance. Circulation 1995;91:1676-88.
Early and late assessment of the Micro Stent PL coronary stent for restenosis and suboptimal balloon angioplasty J o h n G. Webb, MD, a J e f f r e y J. P o p m a , MD, b A l e x a n d e r J. L a n s k y , MD, b R o n a l d G. Carere, MD, a A l a n Rabinowitz, MD, a Joel Singer, Ph.D., a a n d A r t h u r Dodek, MD a Vancouver, British Columbia,
Canada, and Washington, D.C.
This prospective study represents the initial assessment of the Micro Stent PL (Arterial Vascular Engineering, Inc.) coronary stent. From one to three radiopaque stainless steel stents, each measuring 4 mm long, were premounted onto specially designed balloon catheters. A total of 123 stents were implanted in 41 patients without procedural failure or complications. Stent dislodgment proved a concern, with 7 of 123 stents (5.7%) moving >3 mm from the site of placement and late downstream migration occurring in an additional patient. Subacute stent thrombosis occurred in two patients (5%). Six-month angiographic follow-up was available in 37 of 41 patients (90%). Minimal lumen diameter at baseline was 0.93 ± 0.51 mm, increasing to 2.74 ± 0.49 mm after stenting, and falling to 1.66 ± 0.89 mm at 6 months; this represents a late loss of 60% of the initial gain. Restenosis, based on a binary definition of >50% diameter stenosis, was documented in 18 patients (49%). Advantages of the Micro Stent PL include its radiopacity and marked ease of distal delivery. The potential for stent dislodgment has implications for future stent designs. The role of the Micro Stent PL in managing restenosis is unclear, but it appears useful in the management of dissection and threatened closure after balloon angioplasty. (Am Heart J 1997;133:369-74.)
C o n s i d e r a b l e experience h a s b e e n g a i n e d w i t h t h e P a l m a z - S c h a t z stent, 1"3 t h e W a l l s t e n t , 4 t h e G i a n t u r c o - R o u b i n F l e x S t e n t , 5-7 a n d t h e W i k t o r stent. 8, 9 P r e l i m i n a r y a s s e s s m e n t of t h e Micro S t e n t P L (Arterial V a s c u l a r E n g i n e e r i n g Inc., S a n t a Rosa, Calif.) a n d its p r o t o t y p e device h a s b e e n reported. 1°, 11 We p r e s e n t t h e initial a n d late clinical a n d a n g i o g r a p h i c e v a l u a t i o n of t h e Micro S t e n t PL. From the aInterventional Cardiology Group, St. Paul's Hospital, University of British Columbia, and bWashington Hospital Center. Reprint requests: John G. Webb, MD, 502-1160 Burrard St., Vancouver, B.C., Canada V6Z 2E8. Copyright © 1997 by Mosby-Year Book, Inc. 0002-8703/97/$5.00 + 0 4/1/75871
METHODS Device description. The Micro Stent PL is constructed
of 316L stainless steel wire with a cross-sectional diameter of 0.008". A single circular strand is fashioned such that each stent has a total of eight longitudinal struts with four crowns at either end. Individual stents are 4 m m long with a nonexpanded profile of 0.065" (Fig. 1). Monorail or coaxial dual marker balloons measure 6, 10, and 15 m m long to accommodate one, two, or three stents, respectively. The compliant polyethylene balloon material is heat shrunk and slightly redundant to partially envelope the stent struts. Study protocol. Eligible patients had either restenosis or suboptimal results/threatened closure after balloon angioplasty and were able to give informed consent. The study protocol was approved by research review committees of St. Paul's Hospital, the University of British Columbia, and the Bureau of Medical Devices, Department of Health and Welfare, Canada. After 6 months of clinical follow-up, patients underwent coronary angiography. Stent procedure. Lesions were predilated with a standard angioplasty balloon. From one to three stents were deployed to just above the nominal pressure of 6 atm (mean 7.8 + 2.4 arm). During the study, high:pressure inflations, oversized balloons, and intravascular ultrasound were not routinely used, although all three modalities were used in selected patients. Patients were premedicated with aspirin. Heparin (10,000 units) was administered and the activated clotting time was maintained above 300 seconds. Dextran was begun during the procedure at a dosage of 50 ml/hour for a total of 1,000 ml. Sheaths were removed 4 hours after the procedure and heparin was reinstituted 4 hours later. Warfarin (international normalized ratio >2.5) was continued for 1 month and aspirin was continued indefinitely. Qualitative and quantitative angiographic outcomes.
Angiograms were analyzed by the Washington Hospital 369
370 Webb et al.
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Fig. 1. Micro Stent PL. Left, Single and triple premounted, 4 mm long stents. Middle, Balloon expansion. Right, Three fully expanded stents. Angiographic Core Laboratory using standard qualitative morphologic and quantitative angiographic criteria.12 Two projections demonstrating the stenosis in its sharpest and tightest views were selected for quantitative analysis. Cineframes were magnified optically 2.0:1 to 2.5:1 and digitized into a 512 x 512 x 8-bit pixel matrix using a cinevideo converter and a CAP-35 mm (General Electric, Milwaukee, Wis.) interfaced to an 80406 computer that used Cardiovascular Measurement System analysis.12The image is calibrated with the contrast-filled catheter serving as the reference source. Minimal lesion diameter and interpolated reference diameter were used to calculate percent diameter stenosis. Statistical analysis. All data are expressed as the mean value -+ SD. Comparisons were performed using t tests for continuous variables and the chi-square test for dichotomous variables. A statistical probability ofp -< 0.05 was considered significant. RESULTS Study patients. Forty-one patients were enrolled between March 1994 and J a n u a r y 1995, with suboptimal results or threatened closure after balloon angioplasty in 20 patients and restenosis in 21. Mean age was 61 _+ 10 years, with 36 male patients (88%) and 10 diabetic patients (24%). Single-vessel disease was present in 22 (54%), double-vessel disease in 13 (32%), and triple-vessel disease in 6 (14%). Left ventricular ejection fraction was 65% _+ 11%. Twentyeight patients (68%) had a prior history of percutaneous transluminal coronary angioplasty (PTCA), 9
(22%) had had bypass surgery, and 24 (59%) had had infarction. Patients undergoing stent implantation for restenosis tended to be older t h a n patients with threatened closure (64 vs 57 years, p < 0.05) and were less likely to have coronary occlusion (Thrombolysis in Myocardial Infarction [TIMI] trial perfusion grade 0 or 1) before angioplasty (1 vs 5, p = 0.03). The stented artery was the left anterior descending artery in 18 patients (43%), the circumflex artery in 9 (21%), the right artery in 12 (29%), and a vein graft in 3 (7%). The lesion was ostial in 2 patients (5%), proximal in 17 (42%), midvessel in 18 (44%), distal in 2 (5%), and anastomotic in 2 (5%). TIMI grade <3 was noted in 9 patients (22%), thrombus in 6 (15%), eccentricity in 11 (27%), a bifurcation in 16 (39%), moderate or severe calcification in 9 (22%), and irregularity in 12 (29%). Average lesion angulation was 24 _+ 16 degrees, and average length was 10.2 _+ 0.5 mm. Procedural outcome..One hundred twenty-three stents were implanted in 44 coronary vessels. From one to eight stents (mean 2.8) were implanted per vessel. The initial deployment involved a single stent in 4 patients (9.5%), two stents in 24 (57%), and three stents in 14 (33%). A second deployment was used in 15 patients, with a single stent in 7 (17%), two stents in 8 (19%), and three stents in 2 (5%). Three patients required a third deployment.
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Fig. 2. A, Acute inferior infarction with right coronary occlusion. B, Initial balloon dilation is unsuccessful. C, A spiral dissection extends from proximal artery to beyond crux. D, Gianturco-Roubin FlexStent stent could only be advanced as far as midvessel. E, Palmaz-Schatz stent would not cross previously placed stent.
Fig. 3. A, Slow outflow and occlusion of posterior descending branch remains. B, Six Micro Stent PL devices were easily advanced through both previously placed stents and deployed in distal artery. C, The proximal Palmaz-Schatz stent is not visible (open arrow), the FlexStent is dimly seen (curved arrows), yet Micro Stent PL is easily seen (straight arrows). D, Artery remains patent at 4-month follow-up despite persistent visible dissection. All stenting procedures were successful. No difficulty was encountered passing the stent delivery system through a standard lumen rotating hemostatic valve or standard 8F (0.078" to 0.084" inter-
nal diameter) guiding catheters. Stents were easily visualized by fluoroscopy. Stents were easily delivered into distal vessels through tortuous anatomy and through previously placed stents (Figs. 2 and 3).
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Fig. 4 A, Previously totaled occluded saphenous vein graft remains patent 4 months after intracoronary thrombolysis and angioplasty. Residual anastomotic stenosis is present. B, Two stents are easily advanced across stenosis. C, Stents have slid slightly to either side of most severe stenosis, requiring placement of third stent. D, Third stent is easily advanced between two previously placed stents. E, Good stent placement is accomplished. F, Graft remained patent at 6-month angiographic follow-up.
Table I. Clinical outcome
Six-month follow-up
In hospital
~of
~of
No. of total No. of total Complications complications patients complications patients Death Cardiac surgery Infarction Stent occlusion Stent PTCA Vascular complications Any of the above
0 0 0 0 2 0
0 0 0 0 5 0
0 2 2 2 8 0
0 5 5 5 20 0
2
5
10
25
In our series, stenting over side branches did not impair flow and side branches were easily dilated in two patients with bifurcation lesions. In no case did a stent become dislodged from the
balloon catheter before planned deployment. However, in six patients (14%), significant (->3 mm) stent movement (7 of 123 stents, 5.7%) was documented after deployment at the initial procedure. Dislodgment occurred as a result of slippage on the shoulder of a bulky lesion (two stents) or at a bend point (one stent), at withdrawal of the deflated stent delivery balloon (two stents), or on recrossing with a previously inflated winged balloon (two stents). In another instance the most distal of three stents implanted in the proximal lefLanterior descending artery was found at 6-month follow-up to have migrated 10 mm downstream. In no case was stent dislodgment associated with complications other than the necessity of implanting additional stents (Fig. 4). Clinical o u t c o m e . In-hospital and follow-up (6 month) clinical outcome is presented in Table I. No patient required urgent coronary artery bypass, vascular repair, or transfusion, had a myocardial in-
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farction, or died. All patients were free of angina at discharge. At 6-month follow-up, 21 patients (52%) remained in Canadian Cardiovascular Society class 0 or 1, 5 (13%) in class 2, 8 (21%) in class 3, and 5 (13%) in class 4. At follow-up two patients (5%) had suffered a myocardial infarction, eight patients (20%) had undergone a second PTCA procedure, two patients (5%) had undergone elective coronary artery bypass, and two patients (5%) experienced stent occlusion. There were no deaths. Angiographic outcome. Postprocedural angiography documented thrombus in two patients (5%). Type A dissections (luminal haziness) remained in two patients (5%), type B (linear dissection) remained in 2 (5%), and type C (extraluminal contrast) remained in two (5%), with a mean dissection length of 3.4 _+ 2.0 mm. 12 Quantitative coronary angiographic outcomes are listed in Table II. Baseline minimal lumen diameter (MLD) was 0.93 _+ 0.51 mm and increased to 2.74 +_ 0.49 mm after stenting (p < 0.001). In the subgroup of patients with threatened closure, MLD increased from 1.95 _+ 0.77 mm after balloon angioplasty alone to 2.60 + 0.55 mm after stenting (p < 0.001). Follow-up angiography was available in 37 patients (90%). At follow-up MLD fell to 1.66 _+ 0.89 mm (p < 0.001), representing a late loss of 60% of the initial gain. As determined by CMS, the percent diameter stenosis before the initial procedure was 67% _+ 22%, after stenting it was 14% _+ 21%, and at follow-up it was 47% _+ 23%. Restenosis (using a binary definition of >50% diameter stenosis) was present in 49% of all lesions, 44% of restenotic lesions, and 56% of suboptimal angioplasty lesions. In patients with restenosis, intimal proliferation was often visible as a lucency separating the stent struts and opacified arterial lumen. Stent thrombosis. In-hospital stent thrombosis did not occur. Post hospital thrombotic stent occlusion occurred in two patients (5%) at 5 and 7 days. These two events accounted for the 5% incidence of late myocardial infarction in this series. In one patient aspirin and warfarin h a d been discontinued in error after stenting of a complex dissection and threatened closure. The second patient had a complex dissection tacked up by a single 4 mm stent. It was apparent that an insufficient length of the artery had been stented and additional stents were implanted. Both vessels remained patent at 6-month follow-up angiography. DISCUSSION
This experience demonstrates that the Micro Stent PL is associated with a favorable early outcome in
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Table I]. Quantitative angiographic results Measure Reference d i a m e t e r Baseline Final Follow-up Minimal l u m e n d i a m e t e r Baseline Final Follow-up D i a m e t e r stenosis Baseline Final Follow-up Stenosis ->50%
Result
3.19 _+ 0.50 m m 3.32 +- 0.57 m m 3.08 _+ 0.44 m m 0.93 _+ 0.51 m m 2.74 _+ 0.49 m m 1.66 _+ 0.89 m m 67% -+ 22% 14% -+ 21% 47% _+ 23% 18/37 (49%)
patients with prior restenosis or suboptimal balloon angioplasty. The short length of the stents allows the operator to match the number of stents to the length of the lesion and favors delivery through tortuous anatomy. Radiopacity allows accurate stent positioning and confirmation of deployment, while the relatively open design allows opacification of the arterial lumen within the stent confines despite the radiopacity of the stent struts. The potential for stent dislodgment is a limitation of this stent design. The longitudinal orientation of the smooth, nonoverlapping stent struts favors easy advancement, but it may not always securely adhere to the arterial wall. We recommend slight oversizing of the Micro Stent PL, waiting for full balloon deflation before withdrawing the delivery balloon under fluoroscopy. Furthermore, recrossing a recently deployed stent should be avoided if possible. Clinical outcomes compare favorably with those reported in other series of coronary stenting, 1-9 with no infarction, emergency surgery, or mortality in this relatively high-risk group. Subacute stent thrombosis did occur in two patients in whom stents were implanted for threatened closure, a condition that may predispose to stent thrombosisfl 5-7, 13 This 5% incidence of stent thrombosis (95% confidence interval 0% to 12%) compares favorably with other early reports of bailout stenting of 3.5% to 8% with the Palmaz-Schatz stent,1, 13, 147% with the FlexStent, 5-7 and 17% with the Wiktor stent, s Vascular complications were notably absent in this study, despite the aggressive anticoagulation required by the study protocol. A binary restenosis rate of 49% (95% confidence intervals 33% to 65%) seems high when compared with other stent series. 2-4, 14 This may reflect a study population composed of patients at high risk of restenosis, including those with prior restenosis, 15
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suboptimal balloon angioplasty, 16 and recanalized total occlusions. 17, is In vitro testing has determined that, for an average vessel of 3.5 mm, the expanded Micro Stent PL will cover 8.4% of the luminal surface area. Although speculative, a low surface area and relatively deep penetration into the arterial wall may adversely affect the arterial response to stenting. This study of necessity represents a learning curve, and patient numbers prohibit direct comparison of event rates with other stents. The study protocol was designed at a time when anticoagnlation protocols were more aggressive than are currently thought necessary and was performed before recent trends in stenting techniques such as high-pressure balloon inflation and oversizing. 19 In conclusion, the advantages of the Micro Stent PL include its ease of distal delivery through tortuous anatomy, its radiopacity, and t h e ability to incrementally stent lesions of varying length. Caution is required due to the potential for stent dislodgment. Future articulated modifications of this basic stent design (the Micro Stent) have been developed on the basis of this experience and appear likely to reduce this concern. The role of this stent in managing restenosis is unclear. However, the Micro Stent PL appears useful in managing suboptimal results and threatened closure after balloon angioplasty. REFERENCES
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