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Stent implantation of saphenous vein graft aorto-ostial lesions in patients with unstable ischemic syndromes: Immediate angiographic results and long-term clinical outcome

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Stent implantation of saphenous vein graft aorto-ostial lesions in patients with unstable ischemic syndromes: Immediate angiographic results and long-term clinical outcome
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  866 JACC gol. 25, No. 4 March 15, 1995:866-70 Stent Implantation of Saphenous Vein Graft Aorto Ostial Lesions in Patients With Unstable Ischemic Syndromes: Immediate Angiographic Results and Long Term Clinical Outcome ELDAD RECHAVIA, MD, FRANK LITVACK, MD, FACC, GAIL MACKO, RN, NEAL L. EIGLER, MD, FACC Los Angeles, California Objectives. This study examined the immediate angiographic and long-term clinical results of stenting saphenous vein graft aorto-ostial stenosis at a single center. Background. Data on the feasibility, safety and short- and long-term clinical results of stent implantation in aorto-ostial lesions in patients with unstable angina are limited. Methods. Paimaz or Palmaz-Schatz stents were deployed in 29 patients (mean [-+SD] age 70 -+ 10 years) with complex (B2 or C) vein graft aorto-ostial lesion morphology. All patients had angina at rest; 23 (79%) had a previous myocardial infarction; and 13 (45%) had two previous bypass operations (mean graft age 9 -+ 5 years). Mean left ventricular ejection fraction was 42 -+ 13%. Results. Thirty-two stents were deployed in 25 new and 4 restenotic aorto-ostial lesions. Ten additional stents were im- planted in five patients for eight lesions other than at ostial locations. Stent implantation was successful in all patients. There was no death, Q wave myocardial infarction, bypass surgery or stent thrombosis in the first 30 days. Stenting improved minimal lumen diameter from 0.7 -+ 0.5 mm (95% confidence interval [CI] 0.5 to 0.8) to 3.3 + 0.5 mm (CI 3.2 to 3.5) and percent diameter stenosis from 80 -+ 13% (CI 75% to 85%) to 1 -+ 12% (CI -3% to 6%) (p < 0.001 for both variables). Immediate loss from recoil was 0.2 -+ 0.2 mm (CI 0.2 to 0.3), corresponding to a percent recoil of 7 -+ 5% (CI 5% to 9%). Clinical follow-up in all patients at a mean of 11 -+ 8 months revealed that 27 patients (94%) were free of death or myocardial infarction. Bypass surgery and balloon angioplasty were required in one (3%) and two (6%) patients, respectively. In 21 (88%) of the remaining 24 patients, symptoms were lessened by two or more symptom classes. Conclusions. Palmaz or Paimaz-Schatz stent implantation for saphenous vein graft aorto-ostial stenosis has a high likelihood of immediate success and is associated with a large immediate gain in lumen diameter. Thirty-day and long-term adverse event rates are low. These data suggest that stenting saphenous vein graft aorto-ostial lesions is an acceptable therapeutic option in selected elderly patients with unstable angina and large-diameter vessels. J Am Coil Cardiol 1995;25:866-70) Aorto-ostial location is an important predictor of early and late failure of conventional balloon angioplasty in both native arteries and saphenous vein grafts (1-6). Experience with second-generation interventional devices, including excimer laser coronary angioplasty and directional, rotational and extraction atherectomy, suggests that the once difficult to treat aorto-ostial lesion can be approached with a high probability of success and low complication rates (7-11). This notwithstand- ing, immediate lumen loss from recoil and late restenosis remains problematic. Coronary stenting of nonostial lesions with the Palmaz-Schatz coronary stent is associated with the From the Cardiovascular ntervention Research Center, Division of Cardi- ology, Department of Medicine and Medical Research Institute of Cedars-Sinai Medical Center and University of California-Los Angeles School of Medicine, Los Angeles, California. Dr. Rechavia s the recipient of an American Physicians Fellowship, Brookline, Massachusetts and is supported in part by the Save A Heart Foundation, Los Angeles, California. Manuscript received September 12, 1994; revised manuscript received October 17, 1994; accepted October 21, 1994. Address for corresnondence: Dr. Neal L. Eigler, Cardiovascular ntervention Center, Cedars-Sinai Medical Center, 8700 Beverly Boulevard, Room 6558, Los Angeles, California 90048. largest immediate gain of any interventional device and has a low rate of restenosis (12). This report details our short-term and follow-up single-center experience with Palmaz or Palmaz- Schatz stents implanted in saphenous vein graft aorto-ostial locations in a group of elderly patients with acute unstable ischemic syndromes. Methods Patients. Between March 1992 and June 1994, 29 patients (mean [+SD] age 70 + 10 years, range 45 to 84; 25 men [87%], 4 women [13%]) had stents placed in aorto-ostial locations (-<3 mm from the vein graft vessel aortic srcin) at Cedars- Sinai Medical Center. Patients were referred for this proce- dure if they had active ischemia related to the treated vessel; if they failed another intervention or were deemed suboptimal candidates for alternative treatment with other revasculariza- tion procedures, including bypass surgery; or if the target vessel was large enough to accept a stent ->3 mm in diameter, and there was adequate runoff. The demographics of the patient cohort are summarized in Table 1. Twelve patients 01995 by the American College of Cardiology 0735-1097/95/ 9.50 0735-1097(94)00457-2  JACC Vol. 25, No. 4 RECHAVIA ET AL. 867 March 15, 1995:866-70 STENTS IN OSTIAL VEIN GRAFT LESIONS Table 1. Clinical Characteristics of 29 Study Patients Gender Male 25 (87%) Female 4 (13%) Mean age (yr) 70 _+ 10 Range (yr) 45-84 Risk factors for CAD Smoking 11 (38%) Hypertension 18 (62%) Diabetes 4 (14%) Hypercholesterolemia (>200 mg%) 11 (38%) Extent of CAD Prior MI 20 (69%) Recent MI 5 (17%) Prior multiple CABG 13 (45%) Mean graft age (yr) 9 + 5 Range (yr) 1-20 Mean LVEF (%) 42 _+ 13 Range (%) 25-68 Data presented are mean value _+ SD or number (%) of patients. CABG = coronary artery bypass operation; CAD - coronary artery disease; LVEF - left ventricular ejection fraction; MI - myocardial infarction. (41%) were >75 years old; 23 (79%) had a history of myocar- dial infarction, including 5 (17%) with recent (within 30 days) myocardial infarction; and 13 (45%) had undergone operation twice. Mean saphenous vein graft age was 9 + 5 years. All patients had multivessel coronary artery disease and presented to hospital with unstable angina (Canadian Cardiovascular Society class IV). Eleven (38%) patients had left ventricular failure. Mean left ventricular ejection fraction assessed by contrast ventriculography or gated blood pool radionuclide study in 25 (86%) patients was 42 +_ 13% (95% confidence interval [CI] 37% to 48%). Stent implantation. All patients had stenotic lesions (->50% diameter) involving the ostium of the vein graft vessel. All prestent lesions (25 new and 4 restenotic) were in morpho- logic class B2 (69%) or C (31%) according to the modified American College of Cardiology/American Heart Association criteria (3). One patient (3%) underwent rescue stenting in the setting of a suboptimal result after balloon angioplasty. Pa- tients received premedication with aspirin (325 rag/day) and dipyridamole (75 mg three times a day). Heparin was given during the procedure, maintaining the activated clotting time >300 s. A total of 42 stents were implanted (32 in ostial and 10 in nonostial locations), including 40 Palmaz-Schatz 15-mm artic- ulated stents and two 10-mm Palmaz biliary stents. Stents were deployed using the femoral approach, except one case where a brachial access was used. All lesions were predilated with undersized balloon catheters. Stents were positioned so that -1 mm of their proximal ends extended into the aortic root. After initial deployment, all stents were further expanded with large or high pressure balloons to leave a minimal residual stenosis. An oversized compliant balloon was used to flare the portion of the stent extending into the aorta. Continuous heparin infusion was started after arterial sheath removal and adjusted according to the activated partial thromboplastin time until oral anticoagulation therapy was stabilized. Antiplatelet and warfarin therapy were continued as previously recom- mended (13). Data analysis. All data were gathered prospectively in a registry data base. Cineangiograms were analyzed by a single experienced observer (E.R.) without previous knowledge of the clinical outcome. The severity of the stenosis was measured using an automated computer-assisted edge detection algo- rithm with magnification calibrated from the guiding catheter diameter (Imagecomm Systems), as reported elsewhere (7). The projection that best demonstrated the target lesion was selected throughout the study. End-diastolic frames with the most severe narrowing were selected, and the following mea- surements were obtained: 1) reference vessel diameter, 2) minimal lumen diameter, 3) lesion length, and 4) maximal balloon diameter after stent deployment. Percent diameter stenosis was calculated using the minimal and reference vessel diameters. Recoil was calculated as the difference of the maximal measured balloon diameter during stent deployment and the postprocedural minimal lumen diameter divided by maximal balloon diameter. Procedure success was defined as successful stent deployment and residual stenosis <30% in the absence of major events during the hospital period (subacute thrombosis, bypass surgery, Q wave myocardial infarction, death) or a need for revascularization (target vessel or other) by surgical or catheter-based intervention during the first 30 days. Serum creatine kinase (CK) levels were measured, and a 12-lead electrocardiogram was obtained after the procedure and the next morning. Infarction was diagnosed if total CK level was >200 IU with positive (>5%) MB isoforms. Long-term clinical follow-up was obtained using a standard questionnaire, sent to the patient's physician or by return clinic visits. These data included the same adverse events and symptom classification (Canadian Cardiovascular Society clas- sification). Late stress tests were performed at the descretion of the referring physicians. Follow-up angiography was per- formed for clinical indications only. Restenosis was defined as ->50% diameter narrowing at the stented aorto-ostial site. Statistical analysis. For all variables, data are presented as mean value _+ SD with 95% confidence interval (CI) values. Pairwise comparisons between variables were performed with the Student t test. A p value <0.05 was considered significant. Results Immediate results are summarized in Table 2. Single-lesion stent implantation was performed in 21 patients (72%). Eight procedures (28%) were multivessel or multilesion interven- tions. In five patients, 10 additional stents were deployed in eight lesions other than the ostial lesions, and in three other patients, four additional lesions were treated by balloon angio- plasty at the same setting. Single stents were placed in 26 ostial lesions (90%) and two overlapping stents in another 3 lesions (10%). In one patient (3%), stent implantation was indicated because of a suboptimal result of balloon angioplasty. Mean  868 RECHAVIA ET AL. JACC VoL 25, No. 4 STENTS IN OSTIAL VEIN GRAFT LESIONS March 15, 1995:866-70 Table 2. Angiographic Data Before and After Stenting Before stenting Lesion length (mm) 7.l _+ 2.8 Reference vessel diameter (ram) 3.2 + 0.6 MLD (mm) 0.7 _+ 0.5 Percent diameter stenosis 80 _+ 13 After stenting Reference vessel diameter (mm) 3.4 -- 0.4 MLD (ram) 3.3 + 0.5 Percent diameter stenosis 1 _+ 12 Immediate gain (mm) 2.7 _+ 0.6 Maximal balloon dilatation (ram) 3.6 _+ 0.5 Maximal balloon pressure (atm) 11 + 4 Recoil Amount (ram) 0.2 _+ 0.2 Percent 7 _+ 5 Data presented are mean value _+ SD. MLD - minimal lumen diameter. maximal balloon pressure used for stent deployment was 11 + 4 atm (CI 9 to 12). The balloon was usually inflated to 8 to 10 atm, depending on the stent size and balloon diameter. In the last 15 patients (between July 1993 and June 1994), a relatively higher inflation pressure was used (12 _+ 5 atm) for stent deployment than that in the first 14 patients (10 _ 3 atm, p = NS). Stent implantation and procedural success was achieved in all 29 patients (100%) (Fig. 1). There were no major adverse events, including subacute thrombosis, in the first 30 days. Vascular complications occurred in three patients (10%). One patient needed vascular repair, and two required blood transfusions. Non-Q wave myocardial infarction oc- curred in two patients (7%), which was presumed to result from distal embolization during the procedure. Peak CK levels were 282 and 345 IU. Duration of hospital stay after stent implantation averaged 5 _+ 2 days. Minimal lumen diameter increased more than fourfold, from a mean of 0.7 _+ 0.5 mm (CI 0.5 to 0.8) to 3.3 _+ 0.5 mm (CI 3.2 to 3.5, p < 0.001), and percent stenosis was improved from 80 _+ 13% (CI 75% to 85%) to 1 + 12% (CI -3% to 6%, p < 0.001). Immediate lumen loss or recoil was 0.2 _+ 0.2 mm (CI 0.2 to 0.3), corresponding to 7 -+ 5% (CI 5% to 9%) relative recoil. Normal reference diameter increased significantly from 3.2 _+ 0.6 mm (CI 2.9 to 3.4) before to 3.4 _+ 0.4 mm immediately after (CI 3.2 to 3.4) the procedure (p < 0.001). Clinical and angiographic follow-up. All 29 patients were followed up for a mean of 11 _+ 8 months (range 2 to 27). One patient (3%) died 8 months after stent implantation. The cause of death was related to progressive left heart failure without angiographic confirmation of the stented vessel patency. One patient (3%) had a myocardial infarction, and another (3%) required bypass reoperation (Fig. 2). Symptom- or stress testing-guided repeat angiography was performed in five patients (17%) at an average 5 _+ 2 months after stenting. Target vessel restenosis was found in four patients. Balloon angioplasty was successful in two patients and was not at- tempted in the two other patients where total occlusion was found. Of the 24 patients who were free of major adverse Figure 1. Top, Baseline right anterior oblique projection of a saphe- nous vein graft angiogram showing 96% stenosis of an eccentric aorto-ostial lesion. Bottom, Angiogram taken after deployment of a single Palmaz-Schatz coronary stent showing a widely patent vein graft (measured residual stenosis of 3%) to the left anterior descending coronary artery. clinical events or the need for repeat intervention, 8 (33%) were free of angina, 13 (55%) were in Canadian Cardiovascu- lar Society class I (n = 9) or II (n = 4), and 3 (12%) were in class III (n = 2) or IV (n = 1). Discussion This report documents a single center's experience with implantation of slotted-tube stainless steel balloon-expandable stents in saphenous vein graft aorto-ostial stenoses in patients with unstable ischemic syndromes. The majority of patients were considered to be poor surgical candidates and at in- creased risk for a second or third bypass operation because of advanced age, poor left ventricular function or their general status. They represent a high-risk cohort of patients who may benefit the most from effective nonsurgical intervention. Our results demonstrate that stents can be placed in the aorto-ostial location with high primary success rate and paucity of peripro- cedure and long-term cardiac events in these high risk patients.  JACC Vol. 25 No. 4 RECHAVIA ET AL. 869 March 15 1995:866-70 STENTS IN OSTIAL VEIN GRAFT LESIONS PROCEDURE SUCCESS 29/29(100 ) Late follow-up 11+8 months MI DEATH EVENT FREE PTCA CABG 1/29(3 ) 1/29(3 ) 24/29(83 ) 2/29(7 ) 1/29(3 ) ANGINA FREE CLASS I CLASS II CLASS III CLASS IV 8/24{33 ) 9124{38 ) 4/24{17 ) 2/24{8 ) 1124{4 ) Figure 2. Long-term ollow-up and Canadian Cardiovascular Society angina class after stent deployment n 29 patients with unstable angina (angina class IV) with saphenous vein graft aorto-ostial lesions. CABG = coronary artery bypass grafting; MI = myocardial nfarction; PTCA = percutaneous ransluminal coronary angioplasty. These results are encouraging when one considers the ad- vanced graft age (9 _+ 5 years) in this group of patients, the acuity of their clinical presentation and the placement of multiple stents in eight patients (28%). Treatment of aorto ostial lesions. Balloon angioplasty of aorto-ostial stenoses has a low primary success rate, a high complication rate and a high incidence of restenosis (1). The difficulty in treating these lesions stems largely from the apparent paradox that they tend to be both rigid and highly elastic (1). Several reports (7-12) have demonstrated that patients with aorto-ostial stenosis, apart from ostial left main coronary artery stenosis, are well suited for either excimer laser coronary angioplasty or directional or rotational atherectomy. The available data in peer-reviewed published reports (14-19) on stent implantation for aorto-ostial lesions have been based on experience with relatively few patients. To our knowledge, no randomized study comparing different treatment modalities has been published; therefore, no modality can conclusively be recommended for ostial lesions. Nevertheless, stents, when applicable, may be more effective than other devices in dimin- ishing the effect of elastic recoil as well as early and late restenosis (12,20,21). Stents appear best suited for discrete lesions in arteries ->3 mm in diameter that are balloon expandable. For rigid or nondilatable lesions that resist effec- tive stent expansion, a reasonable strategy may be to debulk the lesion first with an atherectomy device or excimer laser. This combination has the potential of achieving a larger lumen dimension than balloon angioplasty or debulking devices used alone. Effectiveness of stenting saphenous vein graft aorto ostial lesions. The mechanical advantages of stenting may be ideally suited for the aorto-ostial saphenous vein graft lesion. In the present study, the immediate gain in diameter was 2.7 _+ 0.6 mm, with only 7% loss from immediate recoil responsible for an average 0.2-mm loss in lumen diameter. This compares favorably with excimer laser balloon angioplasty in similar vein graft lesions with identical reference diameters (3.4 -+ 1.1 mm) and relatively shorter lesion lengths (4.1 _+ 4.3 mm), where procedural success was 91%, estimated recoil 35% (1 mm of immediate loss), immediate gain 1.3 -+ 0.5 mm and residual stenosis 36 _+ 15% (7). Our present data suggest that these stents are sufficiently crush-resistant to overcome the increased elasticity and external stent compression of the aorto-ostial junction. Subacute thrombosis still remains a major limitation of stent implantation. None of our patients had early stent thrombosis, and, consequently, no potential difference in thrombosis rate between patients treated with single versus multiple stents could have been detected. This may be related to the achievement of optimal stent expansion and selection of patients with relatively large vessels with brisk runoff. A recent report (22) suggests that prolonged anticoagulation with hep- arin and warfarin may not be necessary in such patients, which could potentially decrease the 5-day length of stay and the 10% incidence of bleeding and vascular complications reported here. However, it is not inconceivable that stenting an aorto- ostial lesion warrants a longer period of anticoagulation in view of slight stent protrusion into the aorta and the potential for producing systemic thromboemboli. Although there was no such episode in our patients with aorto-ostial lesions, we believe that a larger study is needed to determine whether the current therapeutic protocol is adequate to minimize this risk. Late follow-up revealed that 26 (90%) of 29 patients who underwent stenting were free of adverse major events (death, infarction or bypass surgery) at a mean of 12 _+ 9 months. Repeat balloon angioplasty was performed in two patients (7%). In 21 (88%) of the 24 remaining patients, symptoms lessened by two or more symptom classes (Fig. 2). These results are consistent with other reports of stents applied to the body of vein grafts (23) and compare favorably with other new devices for treatment of this anatomic subgroup. Study limitations. Our study is subject to several limita- tions that should be considered when interpreting the results. First, this was a study of a relatively small number of highly selected patients, and thus there are insufficient data to comment on factors responsible for failure and complications. Second, this was a single-center study, which reflects our bias toward patient selection, technique and our learning curve. Third, our patients with aorto-ostial lesions cannot necessarily be rigorously compared with reports of treatment with other devices, especially those applied predominantly to native le- sions in arteries <3 mm in diameter. Finally, the incidence of angiographic restenosis was not assessed and cannot be pre- dicted from the low rate of angiographic follow-up (24). Summary. The study limitations notwithstanding, there are several clinical inferences that can be drawn from our experi- ence. Stent implantation in aorto-ostial saphenous vein graft lesions has a high likelihood of procedural success with rela-  870 RECHAVIA ET AL. JACC Vol. 25, No. 4 STENTS IN OSTIAL VEIN GRAFT LESIONS March 15, 1995:866-70 tively low morbidity and infrequent late adverse clinical events. It is an effective therapeutic option in high risk, elderly patients with unstable ischemic syndromes after bypass surgery who may gain early and long-term clinical benefit from this treat- ment strategy. Stent implantation results in a very large immediate gain with minimal elastic recoil and hence repre- sents a potential advance over other interventional techniques. In view of the current data, our own treatment strategy would be to consider primary stenting for aorto-ostial lesions in _>3-mm diameter vein grafts. In vein grafts or native arteries -<3 ram, we would consider treatment with a debulking device and adjunctive balloon angioplasty. In native arteries that are rigid or calcified and ->3 ram, we would consider first the debulking-angioplasty approach and apply a slotted-tube stent when a minimal lumen diameter of 2 mm could not be achieved or if significant dissection is seen. Careful consider- ation of risk/benefit ratio and health care costs should also be factored into the decision process with regard to stent implan- tation, repeat operation or treatment with other angioplasty devices. References 1. Topoi E J, Ellis SG, Fishman J, et al. Multicenter study of percutaneous transluminal angioplasty, for right coronary artery ostial stenosis. J Am Coil Cardiol 1987;9:1214-8. 2. Ellis SG, Roubin GS, King SB, Douglas G, Weintraub WS, Cox W. Angiographic and clinical predictors of acute closure after native vessel coronary angioplasty. Circulation 1988;77:372-9. 3. Ellis SG, Vandormael MG, Cowley MG, et al. Coronary morphologic and clinical determinations of procedural outcome with angioplasty for multives- sel coronary disease. Circulation 1990;82:1193-202. 4. Hirshfeld JW, Schwartz JS, Jugo R, et al. Restenosis after coronary, angioplasty: A multivariate statistical model to relate lesion and procedure variables to restenosis. J Am Coil Cardiol 1991;18:647-56. 5. Reeder GS, Bresnahan JF, Holmes DR, et al. Angioplasty for aorto- coronary' bypass graft stenosis. Mayo Clin Proc 1986;61:14-9. 6. DeFeyter P J, VanSuylen R J, DeJaegere PPT, Topoi E J, Serruys PW. Balloon angioplasty for the treatment of lesions in saphenous vein grafts. J Am Coll Cardiol 1993;7:1539-49. 7. Eigler N, Weinstock B, Douglas JS, et al. Excimer laser coronary angioplasty of aorto-ostial stenoses: Results of the excimer laser coronary angioplasty (ELCA) registry in the first 200 patients. Circulation 1993;88:2049-57. 8. Pompa J J, Dick RJC, Haudenschild CC, Topoi E J, Ellis SG. Atherectomy of right coronary ostial stenoses: initial and long term results, technical features and histologic findings. Am J Cardiol 1991;67:431-3. 9. Pompa JJ, Brogan WC, Pichard AD, et al. Rotational coronary atherectomy of ostial stenoses. Am J Cardiol 1993;71:436-8. 10. Sabri MN, Cowley MJ, DiSciascio G, et al. Immediate results of interven- tional devices for coronary ostial narrowing with angina pectoris. Am J Cardiol 1994;73:122-5. 11. Koller PT, Freed M, Grines CL, O'Neill WO. Success, complications, and restenosis following rotational and transluminal extraction atherectomy of ostial stenoses. Cathet Cardiovasc Diagn 1994;31:255-60. 12. Kuntz RE, Safiaan RD, Levine MJ, Reis GJ, Diver DJ, Bairn DS. Novel approach to the analysis of restenosis after the use of three new coronary devices. J Am Coil Cardiol 1992;19:1493-9. 13. Schatz RA, Bairn DS, Leon M, et aL Clinical experience with the Palmaz- Scbatz coronary stent: Initial results of a multicenter study. Circulation 1991;83:148-61. 14. Almagor Y, Thomas J, Colombo A. Balloon expandable stent implantation of a stenosis at the srcin of the left internal mammary artery graft. Cathet Cardiovasc Diagn 1991;24:256-8. 15. Nordrehaug JE, Priestley K, Chronos L, Buller N, Sigwart U. Implantation of half Palmaz-Schatz stents in short aorto-ostial lesions of saphenous vein grafts. Cathet Cardiovasc Diagn 1993;29:141-3. 16. Nordrehaug JE, Cbronos L, Denne L, Ricards AF, Bullet N, Sigwart U. Results of stent implantation for the management of aorto-ostial stenoses [abstract]. Br Heart J 1992;68:154. 17. Garcia-Robles JA, Garcia E, Rico M, Esteban E, De Prado AR, Delcan JL. Emergency coronary stenting for acute occlusive dissection of the left main coronary artery. Cathet Cardiovasc Diagn 1993;30:227-9. 18. Macaya C, Alfonso F, lniguez A, Goicolea J, Hernandez R, Zarco P. Stenting for elastic recoil during coronary, angioplasty of the left main coronary artery. Am J Cardiol 1992;70:105-7. 19. Zampieri P, Colombo A, Almagor Y, Maiello L, Finci L. Results of coronary stenting of ostial lesions. Am J Cardiol 1994;73:901-3. 20. Fischman DL, Savage MP, Ellis SG, et al. Restenosis after Palmaz-Schatz stent implantation. In: Serruys PW, Strauss BH, King SB, editors. Restenosis After Intervention With New Mechanical Devices. Boston: Kluwer, i992: 191-205. 21. Kimura T, Nasaka H, Yokoi H, Iwabuchi M, Nobuyoshi M. Serial angio- graphic follow-up after Palmaz-Schatz stent implantation: comparison with conventional balloon angioplasty. J Am Coil Cardiol 1993;21:1557-63. 22. 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