Early Outcome Mter Placement of a Metallic Intracoronary Stent: Initial Mayo Clinic Experience
KIRK N. GARRATT, M.D., DAVID R. HOLMES, Jr., M.D., Division of Cardiovascular Diseases and Internal Medicine; GARY S. ROUBIN, M.B.,B.S., Ph.D., Division of Cardiology, University ofAlabama, Birmingham, Alabama After percutaneous transluminal coronary angioplasty, 3 to 7% of patients have inhospital coronary closure, and the risk of subsequent myocardial infarction is high, even with an urgent bypass operation. Disrupted coronary morphologic integrity, particularly with large dissections, may be associated with an increased risk of acute coronary closure. A percutaneously placed coronary vascular stent may rapidly alleviate acute or threatened coronary closure and could reduce morbidity. Between October 1989 and June 1990, placement of a balloon-expandable, flexible metallic coil (Gianturco-Roubin) coronary stent was attempted 16 times in 15 Mayo Clinic patients-for treatment of actual or threatened abrupt coronary closure in 10 patients, for primary treatment of a lesion judged to be at high risk for dissection with conventional balloon angioplasty in 1, and for elective treatment ofrestenotic lesions in 5. Placement of the stent was successful in 15 attempts (94%). Associated complications, which were uncommon, were similar to those noted after balloon angioplasty. No early deaths occurred, and no patient required coronary artery bypass grafting. Stents were successfully placed in both urgent and elective circumstances in native coronary arteries and saphenous vein grafts, and they were used in primary atheromatous and restenotic lesions. Our initial experience with this metallic coil stent indicates that it is efficacious for vascular disruption that is threatening or causing coronary closure after angioplasty. Furthermore, elective placement of a stent may be safely undertaken in patients with high-risk coronary lesions or recurrent restenotic lesions. The long-term outcome in all groups of patients who receive coronary stents is unknown.
ters, use of an autoperfusion balloon catheter, and urgent intervention with a coronary artery bypass surgical procedure.i" A coronary artery bypass operation for persistent coronary closure is associated with a high risk of myocardial infarction, 9,10,12 which is likely related, in part, to the delay between coronary disruption and surgical revascularization. Catheter-based theraAddress reprint requests to Dr. K. N. Garratt, Division of pies for coronary disruption offer the potential Cardiovascular Diseases, Mayo Clinic, Rochester, MN 55905.
Percutaneous coronary intervention is associated with a 3 to 7% risk of in-hospital coronary closure, primarily related to coronary dissection.':" Established options for management in the event of abrupt vascular closure include use of prolonged inflations ofstandard balloon cathe-
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for rapid resolution of coronary occlusion and for mm in diameter, which was provided by the a reduction in patient morbidity. New potential manufacturer (Cook, Inc., Bloomington, Inditherapeutic techniques include directional coro- ana) already compressed onto a special delivery nary atherectomy for resection of the dissected balloon catheter (Fig. 1). The stent was approxisegment.P'!' remodeling of the vessel wall with mately 20 mm long. The configuration of the laser devices, 15,16 and placement of intracoronary stent allowed radial expansion without shortenstents. Studies in animals and humans indicate ing along the long axis during inflation ofthe dethat percutaneous placement of coronary stents livery balloon. Stent diameters of 2.0, 2.5, 3.0, may be accomplished with acceptable safety and and 3.5 mm were available. efficacy and may be associated with a decreased Procedures.-Before placement of the stent, frequency of subsequent restenosis.F'P stenoses were predilated to the size of the stent Since October 1989, the Mayo Clinic has par- by using conventional angioplasty catheters. ticipated in a multicenter study of a balloon- For 3.0- or 3.5-mm stents, 9-F guiding catheters expandable metallic coil (Gianturco-Roubin) were needed; for smaller stents, 8-F guiding coronary stent. In this report, we describe the catheters were sufficient. The stent delivery initial experience with placement of the first 16 catheter was advanced over a standard anintracoronary stents attempted at the Mayo gioplasty guidewire and into position across the lesion, after which the delivery balloon was Clinic. inflated to expand the stent. After deflation of PATIENTS AND METHODS the balloon, the delivery catheter was gently Study SUbjects.-AlI patients were referred to withdrawn. the cardiac laboratory for diagnosis and treatPlacement of the stent was considered sucment of coronary artery disease. Patients were cessful if the stent was satisfactorily positioned considered eligible for placement of a stent if across the lesion of concern, the stenosis was they had (1) symptoms of coronary dissection improved by 40% or more relative to the predilaor threatened acute closure after balloon tion luminal diameter, and no complication ocangioplasty, atherectomy, or laser procedures curred that resulted in death or a need for that did not respond to usual reparative mea- coronary artery bypass operation during that sures; (2) a high-risk coronary lesion (defined as hospitalization. Any event that resulted in American College of Cardiology/American Heart additional therapy, prolonged hospitalization, Association Task Force type B or type C lesion'") or increased patient morbidity or mortality was that was judged to be at increased risk for considered a complication. Angiography.-The dimensions of the vesdissection with conventional balloon angioplasty; or (3) a restenotic lesion that had resulted in sel before and after dilation and also after placerecurrent symptomatic ischemia. Treated le- ment of the stent were determined by visual sions had to be in vascular segments of 2.0-mm assessment of at least two near-orthogonal diameter or more and could not be located be- views of the vascular segment of concern. The yond an excessively tortuous proximal segment. consensus of at least two experienced angiograPoor guiding catheter support and inability to phers was required. Medications.-Before placement ofthe stent, cross the lesion with a guidewire were contraindications for elective deployment of a stent. patients were premedicated with orally adminIntracoronary thrombus and presence of branch istered aspirin (325 mg three times daily) and vessels did not preclude placement of a stent. dipyridamole (75 mgthree times daily) and with Informed consent was obtained from all pa- intravenously administered heparin (15,000 U). tients, and this investigation was approved by Before the administration of dextran, 100 mg of the Mayo Institutional Review Board. methylprednisolone sodium succinate was given Metallic Coil Stent.-The tested stent con- intravenously to reduce the risk of severe allersisted of a single stainless steel filament, 0.038 gic reactions. Then a 200-ml intravenous bolus
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prednisone and colchicine in an attempt to limit the inflammatory and proliferative response around the stent. Vascular sheaths used for gaining arterial access were usually maintained in place until administration of sodium warfarin had increased the prothrombin time to approximately 14 seconds. The intravenously administered heparin was then reduced until the activated clotting time was less than 200 seconds, after which the sheath was removed and pressure was applied to attain hemostasis. Two hours later, full-dose heparin therapy was resumed and maintained until the prothrombin time had reached 18 seconds. While vascular sheaths were in place, the entry site was examined daily, and sterile dressings with topically applied antibiotics were maintained. Systemic antibiotics were not used. Orally and intravenously administered sedatives and analgesics were used as necessary for patient comfort. Establishing adequate and stable anticoagulation typically required several hospital days after implantation of the stent.
RESULTS
Fig. 1. Diagrams ofGianturco-Roubin intracoronary stent. A, Metallic coil stent is compressed over deflated delivery balloon catheter. B, Inflation of delivery balloon expands the stent, and it remains expanded after deflation and withdrawal of balloon.
of 10% dextran 40 was delivered during a 20- to 30-minute period, followed by an infusion of 100 ml/h until a total of 500 ml had been administered. Intravenous infusion of heparin was continued until anticoagulation could be established with sodium warfarin. At the time of dismissal from the hospital, all patients were receiving an oral regimen of aspirin, dipyridamole, and sodium warfarin. In addition, patients received nitroglycerin and calcium channel antagonists at the time ofimplantation ofthe stent and afterward. Early in the series, patients also received short-term supplemental
Between Oct. 26,1989, and June 18, 1990, placement ofa coronary stent was attempted 16 times in 15 patients at the Mayo Clinic (Table 1). A stent was successfully placed 15 times in 14 patients; in 1 patient, proximal vascular tortuosity prevented safe positioning of a stent. One patient received two coronary stents. Therefore, 15 stents were successfully placed, a primary success rate of 94%. Most patients received a stent as treatment for an unsatisfactory balloon dilation (Table 2). In one patient, complete coronary closure developed in conjunction with angina and electrocardiographic changes, consistent with evolving anterior wall myocardial infarction, within 2 hours after successful balloon angioplasty of a left anterior descending artery that had been complicated by an intimal dissection and 40% luminal narrowing. Nine other patients had clinical or angiographic evidence (or both) of ischemia-producing coronary disruption after balloon angioplasty before leaving the cardiac laboratory (Fig. 2). In some patients, complete
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closure was likely prevented by maintaining the guidewire across the lesion, which provides some support to the disrupted intima. These lesions had a persistent irregular appearance after standard reparative measures were attempted, including multiple prolonged balloon inflations and, in most cases, use of an autoperfusion balloon catheter. Placement of a stent reversed objective evidence of ongoing ischemia in all treated patients. One patient underwent implantation ofa stent as an option to conventional treatment of a high-risk coronary lesion. An additional five patients underwent placement of a stent on an elective basis; elective placement of a stent was undertaken in an attempt to prevent recurrent restenosis in three patients. Stents were successfully placed in eight native coronary vessels and seven saphenous vein grafts (Table 2). Complications were uncommon. In one patient whose heparin infusion was discontinued prematurely, coronary occlusion developed 36 hours after placement of the stent and resulted in prolonged angina and myocardial infarction, which were managed with additional balloon dilation. Three other patients experienced excessive loss of blood at the site of arterial puncture, but no patient sustained a peripheral vascular injury that necessitated surgical intervention or administration of blood transfusions or that resulted in loss of a limb. Two patients became hypotensive during the catheterization procedure associated with the coronary disruption that led to the decision to undertake placement of a stent. One patient with hypotension required intra-aortic balloon pumping before implantation of a stent; after stenting, the hemodynamic status improved. Another patient had hypotension that was not rectified with placement of a stent and required subsequent implantation of an intra-aortic balloon pump. No early deaths occurred in our patients who received stents.
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Table l.-Overview of Patients Who Received Metallic Coil Coronary Stent (Mayo Clinic, October 1989 to June 1990) Factor
No.
Total patients (M:F) Coronary lesions treated Mean age, yr (range) Single-vessel disease Multivessel disease Mean LVEF, % (range)* Indication for stent Dissectiont Acute occlusion Suboptimal dilation'[ High-risk dilation Elective
15 (10:5)
16
63 (43-80)
2
13
64 (42-79)
5 1 4 1 5
*LVEF = left ventricular ejection fraction. tThese morphologic abnormalities remained uncorrected by standard measures and were judged to be at high risk for abrupt coronary closure.
search has been conducted to determine the safety and feasibility of use of percutaneous vascular stent devices. In a phase I human study, the GianturcoRoubin metallic coil stent was implanted as a ''bridge to surgical treatment" in patients with abrupt coronary closure and persistent myocardial ischemia after angioplasty who were ultimately to undergo coronary artery bypass grafting." The stent proved to be effective short-term therapy for occlusive coronary disruptions after angioplasty. In a phase II study, patients underwent deployment of a coronary stent as definitive therapy for abrupt vascular disruption.P" On the basis of the successful results of these initial studies, this stent is now being evaluated in a multicenter phase III trial designed to assess performance in elective implantations after suboptimal dilation, in attempts to reduce the rate of restenosis, and in treatment of acute occlusion. Of the first 16 metallic coil stents implanted in patients at the Mayo Clinic, placement was successful in 94%. Although stents were placed DISCUSSION chiefly in patients with multivessel disease and Percutaneous placement of coiled wire vascular in the setting of symptomatic vascular disrupstents after angioplasty was first successfully tion, including some patients in cardiogenic performed by Charles Dotter more than 20 years shock, no early deaths occurred. Furthermore, ago." During the past decade, extensive re- the incidence ofmajor complications was low; no
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Table 2.--Qutcome After Placement of Metallic Coil Coronary Stent (Mayo Clinic, October 1989 to June 1990)* Factor Placement of stents Attempts Successes (%) Severity of stenosis, mean % ± SD (range) Before stenting After stenting Stented segments SVG LAD-diag RCA-PDA LCX-OM Complications Excessive loss of blood Hypotension Coronary occlusion Prolonged angina Myocardial infarction Death Mean hospital stay, days (range)
No. 16 15 (94) 67.5 ± 15.6 (50-99) 23.0 ± 19.9 (0-90) 7 4 3 1 3 2 2t
It It
o
8.6 (4-23):j:
*Diag = diagonal artery; LAD = left anterior descending artery; LCX = left circumflex artery; OM = obtuse marginal artery; PDA = posterior descending artery; RCA = right coronary artery; SVG =saphenous vein bypass graft. tOne patient had coronary occlusion, prolonged angina, and myocardial infarction. :j:ln one patient, obstruction of the small bowel resulted in a prolonged hospital stay.
patient required a coronary artery surgical procedure to bypass a stented vessel, explant a stent, or repair vascular injuries attributable to attempted placement of a stent. One patient with insufficient anticoagulation sustained a myocardial infarction after thrombotic occlusion of the stented coronary segment; the occlusion was successfully managed with additional balloon dilation. The occlusion after placement of a stent emphasizes the importance of use of anticoagulant and antiplatelet therapies in association with implantation of endovascular prostheses. Studies in animal models demonstrated that development of thrombi over the metallic tines necessitates aggressive anticoagulation during placement of a stent.!? Scanning electron microscopy studies have shown that platelets are deposited immediately after placement of me-
tallic coil stents into blood vessels. 17 Pretreatment with aspirin and dipyridamole decreases vascular occlusion with platelet thrombi. Endothelial and pseudoendothelial cells begin to cover the stent within 1 day; this process may be facilitated by a thin layer of thrombus, inasmuch as endothelial cells usually do not grow well on metallic surfaces.v-" The stent tines are completely covered with confluent cells by 2 weeks in dogs.l? the interval to complete endothelialization in humans is unknown. The amount of metal on which platelets can be deposited may also be an important factor in thrombosis.P? The Gianturco-Roubin stent configuration provides excellent mechanical support of a disrupted vascular wall while maintaining a low ratio of prosthetic material to vessel wall area. Although use of platelet and thrombus inhibitors prevents clinical thrombosis around metallic stents, these agents do not abolish thrombus, as demonstrated in previous studies performed in dogs'" and in pigs." The general utility of an endovascular stent can be appreciated with review of the cardiac catheterization laboratory statistics for our study period. During that time, 595 balloon dilations were performed at the Mayo Clinic, dissection occurred in 237 ofthese, and 48 were associated with abrupt occlusion (Table 3). Most abrupt occlusions were resolved with additional balloon dilations, medical management, or coronary artery bypass grafting. Although many dissections will heal without additional treatment, patients with dissections that cause more than 30% luminal narrowing have an increased risk of in-hospital complete coronary closure (Table 3). Certain morphologic features may also be useful in identifying dissections likely to cause complete vascular closure. 30 The full potential for use of percutaneous stents is currently unknown, but at least some large dissections and occlusions are amenable to stent therapy. Optimal stent characteristics and the ultimate role of such a stent in interventional cardiology have not yet been determined. Several stent designs are being tested clinically, including the Wallstent, which consists of self-expand-
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Fig. 2. Deployment of stent for coronary disruption and threatened vascular closure. A, After balloon angioplasty, proximal left anterior descending coronary artery has a disrupted, irregular .appearance (light arrow) associated with reduced (grade 2, Thrombolysis in Myocardial Infarction classification) blood flow, chest pain, and electrocardiographic changes. B, After placement ofstent, arterial segment is widely patent (dark arrow) and normal blood flow is restored.
ing mesh composed of thin stainless steel filaments'" that continue to exert an outward radial expanding force after deployment, and the Palmaz-Schatz stent, a rigid balloon-expandable slotted metal tube stent that does not flex but is available in an articulated form to facilitate placement in tortuous arteries. 18 The Gianturco-Roubin stent is a flexible stainless steel balloon-expandable stent. Because of its flexibility, the Gianturco-Roubin stent passes easily through guiding catheters and can effectively traverse tortuous coronary segments. In addition, the ability to flex with arterial pulsation may influence subsequent intimal proliferation. Repetitive, cyclic mechanical stress on an arterial wall can provoke intimal hyperplasia" Such cyclic mechanical stress may result from the interplay between arterial pulsations and a continuous outward radial expanding force. Because the Gianturco-Roubin stent does not continue to exert outward radial expanding force after it has been implanted, it should not create substantial cyclic mechanical stress. A mismatch in compliance between two adjacent vascular segments may also be a stimulus for intimal hyperplasia. 32,33 Compliance mis-
match occurs when rigid and compliant vascular segments are juxtaposed and may account for the development of stenoses at anastomotic sites of bypass grafts and other vascular conduits. Because of its flexibility, the Gianturco-Roubin stent minimizes compliance mismatch at the ends of the stent. Experimental studies in at least two animal models'F'" have demonstrated a larger functionallumen and a decrease in neointimal hyperplasia in stented arterial segments in comparison with that normally seen after balloon Table 3.-Frequency of Intimal Dissection and In-Hospital Coronary Occlusion Mter Balloon Angioplasty During the Study Period (Mayo Clinic, October 1989 to June 1990) Severity of dissection (%)*
Lesions (no.)
0 :530 31-60 >60 Total
358 178 39 20 595
Occlusions No. % 22 10 6 10 48
6 6 15 50 8
*Percent of luminal diameter compromised by intimal dissection (visually assessed).
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dilation. Insufficient data are available to determine the effect of flexible metallic coil stents on human restenosis. Alternatives to stainless steel are being considered for the production of coronary stents. Promising new metallic alloys include tantalum, a material with physical and electromechanical properties similar to those of stainless steel but with a much greater density (which would improve visualization of the stent with use of fluoroscopy), and nitinol, a nickel-titanium alloy with "thermal shape memory" properties that allow the material to be ductile at room temperature but attain a prespecified threedimensional configuration when warmed.v' Coating metallic stents with cultured human endothelial cells may accelerate the reendothelialization process after deployment.i" Alternatives to metal alloys are also being considered, including polymeric compounds that may be less thrombogenic, may dissolve after a specified period, and could potentially provide a vehicle for localized delivery of drugs into the vessel wall. Like nitinol, some polymeric materials may have differing configurations at different temperatures. Also under consideration are combinations of metallic and polymeric materials that could provide the mechanical strength and conformability of metallic alloys plus the porosity and low thrombogenicity of polymeric compounds.
CONCLUSION Our initial experience with the flexible metallic coil (Gianturco-Roubin) coronary stent shows it to be a promising device for the treatment of acute and threatened coronary closure after catheter-based intervention. Use of a coronary stent may decrease morbidity in some patients. Metallic coil stents may be safely placed in restenotic lesions and also in primary atherosclerotic lesions; differences in the long-term outcome between these two groups remain uncertain. The ability to place stents presages the ability to implant endovascular prosthetic devices for local administration of drugs, which may decrease the frequency of thrombosis, improve reendothelialization or vascular heal-
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ing after intervention, and diminish the occurrence of restenosis. The long-term outcome of patients in whom intravascular stents have been placed remains to be determined.
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KIRK N. GARRATT, M.D., DAVID R. HOLMES, Jr., M.D., Division of Cardiovascular Diseases and Internal Medicine; GARY S. ROUBIN, M.B.,B.S., Ph.D., Division of Cardiology, University ofAlabama, Birmingham, Alabama After percutaneous transluminal coronary angioplasty, 3 to 7% of patients have inhospital coronary closure, and the risk of subsequent myocardial infarction is high, even with an urgent bypass operation. Disrupted coronary morphologic integrity, particularly with large dissections, may be associated with an increased risk of acute coronary closure. A percutaneously placed coronary vascular stent may rapidly alleviate acute or threatened coronary closure and could reduce morbidity. Between October 1989 and June 1990, placement of a balloon-expandable, flexible metallic coil (Gianturco-Roubin) coronary stent was attempted 16 times in 15 Mayo Clinic patients-for treatment of actual or threatened abrupt coronary closure in 10 patients, for primary treatment of a lesion judged to be at high risk for dissection with conventional balloon angioplasty in 1, and for elective treatment ofrestenotic lesions in 5. Placement of the stent was successful in 15 attempts (94%). Associated complications, which were uncommon, were similar to those noted after balloon angioplasty. No early deaths occurred, and no patient required coronary artery bypass grafting. Stents were successfully placed in both urgent and elective circumstances in native coronary arteries and saphenous vein grafts, and they were used in primary atheromatous and restenotic lesions. Our initial experience with this metallic coil stent indicates that it is efficacious for vascular disruption that is threatening or causing coronary closure after angioplasty. Furthermore, elective placement of a stent may be safely undertaken in patients with high-risk coronary lesions or recurrent restenotic lesions. The long-term outcome in all groups of patients who receive coronary stents is unknown.
ters, use of an autoperfusion balloon catheter, and urgent intervention with a coronary artery bypass surgical procedure.i" A coronary artery bypass operation for persistent coronary closure is associated with a high risk of myocardial infarction, 9,10,12 which is likely related, in part, to the delay between coronary disruption and surgical revascularization. Catheter-based theraAddress reprint requests to Dr. K. N. Garratt, Division of pies for coronary disruption offer the potential Cardiovascular Diseases, Mayo Clinic, Rochester, MN 55905.
Percutaneous coronary intervention is associated with a 3 to 7% risk of in-hospital coronary closure, primarily related to coronary dissection.':" Established options for management in the event of abrupt vascular closure include use of prolonged inflations ofstandard balloon cathe-
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for rapid resolution of coronary occlusion and for mm in diameter, which was provided by the a reduction in patient morbidity. New potential manufacturer (Cook, Inc., Bloomington, Inditherapeutic techniques include directional coro- ana) already compressed onto a special delivery nary atherectomy for resection of the dissected balloon catheter (Fig. 1). The stent was approxisegment.P'!' remodeling of the vessel wall with mately 20 mm long. The configuration of the laser devices, 15,16 and placement of intracoronary stent allowed radial expansion without shortenstents. Studies in animals and humans indicate ing along the long axis during inflation ofthe dethat percutaneous placement of coronary stents livery balloon. Stent diameters of 2.0, 2.5, 3.0, may be accomplished with acceptable safety and and 3.5 mm were available. efficacy and may be associated with a decreased Procedures.-Before placement of the stent, frequency of subsequent restenosis.F'P stenoses were predilated to the size of the stent Since October 1989, the Mayo Clinic has par- by using conventional angioplasty catheters. ticipated in a multicenter study of a balloon- For 3.0- or 3.5-mm stents, 9-F guiding catheters expandable metallic coil (Gianturco-Roubin) were needed; for smaller stents, 8-F guiding coronary stent. In this report, we describe the catheters were sufficient. The stent delivery initial experience with placement of the first 16 catheter was advanced over a standard anintracoronary stents attempted at the Mayo gioplasty guidewire and into position across the lesion, after which the delivery balloon was Clinic. inflated to expand the stent. After deflation of PATIENTS AND METHODS the balloon, the delivery catheter was gently Study SUbjects.-AlI patients were referred to withdrawn. the cardiac laboratory for diagnosis and treatPlacement of the stent was considered sucment of coronary artery disease. Patients were cessful if the stent was satisfactorily positioned considered eligible for placement of a stent if across the lesion of concern, the stenosis was they had (1) symptoms of coronary dissection improved by 40% or more relative to the predilaor threatened acute closure after balloon tion luminal diameter, and no complication ocangioplasty, atherectomy, or laser procedures curred that resulted in death or a need for that did not respond to usual reparative mea- coronary artery bypass operation during that sures; (2) a high-risk coronary lesion (defined as hospitalization. Any event that resulted in American College of Cardiology/American Heart additional therapy, prolonged hospitalization, Association Task Force type B or type C lesion'") or increased patient morbidity or mortality was that was judged to be at increased risk for considered a complication. Angiography.-The dimensions of the vesdissection with conventional balloon angioplasty; or (3) a restenotic lesion that had resulted in sel before and after dilation and also after placerecurrent symptomatic ischemia. Treated le- ment of the stent were determined by visual sions had to be in vascular segments of 2.0-mm assessment of at least two near-orthogonal diameter or more and could not be located be- views of the vascular segment of concern. The yond an excessively tortuous proximal segment. consensus of at least two experienced angiograPoor guiding catheter support and inability to phers was required. Medications.-Before placement ofthe stent, cross the lesion with a guidewire were contraindications for elective deployment of a stent. patients were premedicated with orally adminIntracoronary thrombus and presence of branch istered aspirin (325 mg three times daily) and vessels did not preclude placement of a stent. dipyridamole (75 mgthree times daily) and with Informed consent was obtained from all pa- intravenously administered heparin (15,000 U). tients, and this investigation was approved by Before the administration of dextran, 100 mg of the Mayo Institutional Review Board. methylprednisolone sodium succinate was given Metallic Coil Stent.-The tested stent con- intravenously to reduce the risk of severe allersisted of a single stainless steel filament, 0.038 gic reactions. Then a 200-ml intravenous bolus
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prednisone and colchicine in an attempt to limit the inflammatory and proliferative response around the stent. Vascular sheaths used for gaining arterial access were usually maintained in place until administration of sodium warfarin had increased the prothrombin time to approximately 14 seconds. The intravenously administered heparin was then reduced until the activated clotting time was less than 200 seconds, after which the sheath was removed and pressure was applied to attain hemostasis. Two hours later, full-dose heparin therapy was resumed and maintained until the prothrombin time had reached 18 seconds. While vascular sheaths were in place, the entry site was examined daily, and sterile dressings with topically applied antibiotics were maintained. Systemic antibiotics were not used. Orally and intravenously administered sedatives and analgesics were used as necessary for patient comfort. Establishing adequate and stable anticoagulation typically required several hospital days after implantation of the stent.
RESULTS
Fig. 1. Diagrams ofGianturco-Roubin intracoronary stent. A, Metallic coil stent is compressed over deflated delivery balloon catheter. B, Inflation of delivery balloon expands the stent, and it remains expanded after deflation and withdrawal of balloon.
of 10% dextran 40 was delivered during a 20- to 30-minute period, followed by an infusion of 100 ml/h until a total of 500 ml had been administered. Intravenous infusion of heparin was continued until anticoagulation could be established with sodium warfarin. At the time of dismissal from the hospital, all patients were receiving an oral regimen of aspirin, dipyridamole, and sodium warfarin. In addition, patients received nitroglycerin and calcium channel antagonists at the time ofimplantation ofthe stent and afterward. Early in the series, patients also received short-term supplemental
Between Oct. 26,1989, and June 18, 1990, placement ofa coronary stent was attempted 16 times in 15 patients at the Mayo Clinic (Table 1). A stent was successfully placed 15 times in 14 patients; in 1 patient, proximal vascular tortuosity prevented safe positioning of a stent. One patient received two coronary stents. Therefore, 15 stents were successfully placed, a primary success rate of 94%. Most patients received a stent as treatment for an unsatisfactory balloon dilation (Table 2). In one patient, complete coronary closure developed in conjunction with angina and electrocardiographic changes, consistent with evolving anterior wall myocardial infarction, within 2 hours after successful balloon angioplasty of a left anterior descending artery that had been complicated by an intimal dissection and 40% luminal narrowing. Nine other patients had clinical or angiographic evidence (or both) of ischemia-producing coronary disruption after balloon angioplasty before leaving the cardiac laboratory (Fig. 2). In some patients, complete
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closure was likely prevented by maintaining the guidewire across the lesion, which provides some support to the disrupted intima. These lesions had a persistent irregular appearance after standard reparative measures were attempted, including multiple prolonged balloon inflations and, in most cases, use of an autoperfusion balloon catheter. Placement of a stent reversed objective evidence of ongoing ischemia in all treated patients. One patient underwent implantation ofa stent as an option to conventional treatment of a high-risk coronary lesion. An additional five patients underwent placement of a stent on an elective basis; elective placement of a stent was undertaken in an attempt to prevent recurrent restenosis in three patients. Stents were successfully placed in eight native coronary vessels and seven saphenous vein grafts (Table 2). Complications were uncommon. In one patient whose heparin infusion was discontinued prematurely, coronary occlusion developed 36 hours after placement of the stent and resulted in prolonged angina and myocardial infarction, which were managed with additional balloon dilation. Three other patients experienced excessive loss of blood at the site of arterial puncture, but no patient sustained a peripheral vascular injury that necessitated surgical intervention or administration of blood transfusions or that resulted in loss of a limb. Two patients became hypotensive during the catheterization procedure associated with the coronary disruption that led to the decision to undertake placement of a stent. One patient with hypotension required intra-aortic balloon pumping before implantation of a stent; after stenting, the hemodynamic status improved. Another patient had hypotension that was not rectified with placement of a stent and required subsequent implantation of an intra-aortic balloon pump. No early deaths occurred in our patients who received stents.
271
Table l.-Overview of Patients Who Received Metallic Coil Coronary Stent (Mayo Clinic, October 1989 to June 1990) Factor
No.
Total patients (M:F) Coronary lesions treated Mean age, yr (range) Single-vessel disease Multivessel disease Mean LVEF, % (range)* Indication for stent Dissectiont Acute occlusion Suboptimal dilation'[ High-risk dilation Elective
15 (10:5)
16
63 (43-80)
2
13
64 (42-79)
5 1 4 1 5
*LVEF = left ventricular ejection fraction. tThese morphologic abnormalities remained uncorrected by standard measures and were judged to be at high risk for abrupt coronary closure.
search has been conducted to determine the safety and feasibility of use of percutaneous vascular stent devices. In a phase I human study, the GianturcoRoubin metallic coil stent was implanted as a ''bridge to surgical treatment" in patients with abrupt coronary closure and persistent myocardial ischemia after angioplasty who were ultimately to undergo coronary artery bypass grafting." The stent proved to be effective short-term therapy for occlusive coronary disruptions after angioplasty. In a phase II study, patients underwent deployment of a coronary stent as definitive therapy for abrupt vascular disruption.P" On the basis of the successful results of these initial studies, this stent is now being evaluated in a multicenter phase III trial designed to assess performance in elective implantations after suboptimal dilation, in attempts to reduce the rate of restenosis, and in treatment of acute occlusion. Of the first 16 metallic coil stents implanted in patients at the Mayo Clinic, placement was successful in 94%. Although stents were placed DISCUSSION chiefly in patients with multivessel disease and Percutaneous placement of coiled wire vascular in the setting of symptomatic vascular disrupstents after angioplasty was first successfully tion, including some patients in cardiogenic performed by Charles Dotter more than 20 years shock, no early deaths occurred. Furthermore, ago." During the past decade, extensive re- the incidence ofmajor complications was low; no
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Table 2.--Qutcome After Placement of Metallic Coil Coronary Stent (Mayo Clinic, October 1989 to June 1990)* Factor Placement of stents Attempts Successes (%) Severity of stenosis, mean % ± SD (range) Before stenting After stenting Stented segments SVG LAD-diag RCA-PDA LCX-OM Complications Excessive loss of blood Hypotension Coronary occlusion Prolonged angina Myocardial infarction Death Mean hospital stay, days (range)
No. 16 15 (94) 67.5 ± 15.6 (50-99) 23.0 ± 19.9 (0-90) 7 4 3 1 3 2 2t
It It
o
8.6 (4-23):j:
*Diag = diagonal artery; LAD = left anterior descending artery; LCX = left circumflex artery; OM = obtuse marginal artery; PDA = posterior descending artery; RCA = right coronary artery; SVG =saphenous vein bypass graft. tOne patient had coronary occlusion, prolonged angina, and myocardial infarction. :j:ln one patient, obstruction of the small bowel resulted in a prolonged hospital stay.
patient required a coronary artery surgical procedure to bypass a stented vessel, explant a stent, or repair vascular injuries attributable to attempted placement of a stent. One patient with insufficient anticoagulation sustained a myocardial infarction after thrombotic occlusion of the stented coronary segment; the occlusion was successfully managed with additional balloon dilation. The occlusion after placement of a stent emphasizes the importance of use of anticoagulant and antiplatelet therapies in association with implantation of endovascular prostheses. Studies in animal models demonstrated that development of thrombi over the metallic tines necessitates aggressive anticoagulation during placement of a stent.!? Scanning electron microscopy studies have shown that platelets are deposited immediately after placement of me-
tallic coil stents into blood vessels. 17 Pretreatment with aspirin and dipyridamole decreases vascular occlusion with platelet thrombi. Endothelial and pseudoendothelial cells begin to cover the stent within 1 day; this process may be facilitated by a thin layer of thrombus, inasmuch as endothelial cells usually do not grow well on metallic surfaces.v-" The stent tines are completely covered with confluent cells by 2 weeks in dogs.l? the interval to complete endothelialization in humans is unknown. The amount of metal on which platelets can be deposited may also be an important factor in thrombosis.P? The Gianturco-Roubin stent configuration provides excellent mechanical support of a disrupted vascular wall while maintaining a low ratio of prosthetic material to vessel wall area. Although use of platelet and thrombus inhibitors prevents clinical thrombosis around metallic stents, these agents do not abolish thrombus, as demonstrated in previous studies performed in dogs'" and in pigs." The general utility of an endovascular stent can be appreciated with review of the cardiac catheterization laboratory statistics for our study period. During that time, 595 balloon dilations were performed at the Mayo Clinic, dissection occurred in 237 ofthese, and 48 were associated with abrupt occlusion (Table 3). Most abrupt occlusions were resolved with additional balloon dilations, medical management, or coronary artery bypass grafting. Although many dissections will heal without additional treatment, patients with dissections that cause more than 30% luminal narrowing have an increased risk of in-hospital complete coronary closure (Table 3). Certain morphologic features may also be useful in identifying dissections likely to cause complete vascular closure. 30 The full potential for use of percutaneous stents is currently unknown, but at least some large dissections and occlusions are amenable to stent therapy. Optimal stent characteristics and the ultimate role of such a stent in interventional cardiology have not yet been determined. Several stent designs are being tested clinically, including the Wallstent, which consists of self-expand-
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273
Fig. 2. Deployment of stent for coronary disruption and threatened vascular closure. A, After balloon angioplasty, proximal left anterior descending coronary artery has a disrupted, irregular .appearance (light arrow) associated with reduced (grade 2, Thrombolysis in Myocardial Infarction classification) blood flow, chest pain, and electrocardiographic changes. B, After placement ofstent, arterial segment is widely patent (dark arrow) and normal blood flow is restored.
ing mesh composed of thin stainless steel filaments'" that continue to exert an outward radial expanding force after deployment, and the Palmaz-Schatz stent, a rigid balloon-expandable slotted metal tube stent that does not flex but is available in an articulated form to facilitate placement in tortuous arteries. 18 The Gianturco-Roubin stent is a flexible stainless steel balloon-expandable stent. Because of its flexibility, the Gianturco-Roubin stent passes easily through guiding catheters and can effectively traverse tortuous coronary segments. In addition, the ability to flex with arterial pulsation may influence subsequent intimal proliferation. Repetitive, cyclic mechanical stress on an arterial wall can provoke intimal hyperplasia" Such cyclic mechanical stress may result from the interplay between arterial pulsations and a continuous outward radial expanding force. Because the Gianturco-Roubin stent does not continue to exert outward radial expanding force after it has been implanted, it should not create substantial cyclic mechanical stress. A mismatch in compliance between two adjacent vascular segments may also be a stimulus for intimal hyperplasia. 32,33 Compliance mis-
match occurs when rigid and compliant vascular segments are juxtaposed and may account for the development of stenoses at anastomotic sites of bypass grafts and other vascular conduits. Because of its flexibility, the Gianturco-Roubin stent minimizes compliance mismatch at the ends of the stent. Experimental studies in at least two animal models'F'" have demonstrated a larger functionallumen and a decrease in neointimal hyperplasia in stented arterial segments in comparison with that normally seen after balloon Table 3.-Frequency of Intimal Dissection and In-Hospital Coronary Occlusion Mter Balloon Angioplasty During the Study Period (Mayo Clinic, October 1989 to June 1990) Severity of dissection (%)*
Lesions (no.)
0 :530 31-60 >60 Total
358 178 39 20 595
Occlusions No. % 22 10 6 10 48
6 6 15 50 8
*Percent of luminal diameter compromised by intimal dissection (visually assessed).
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dilation. Insufficient data are available to determine the effect of flexible metallic coil stents on human restenosis. Alternatives to stainless steel are being considered for the production of coronary stents. Promising new metallic alloys include tantalum, a material with physical and electromechanical properties similar to those of stainless steel but with a much greater density (which would improve visualization of the stent with use of fluoroscopy), and nitinol, a nickel-titanium alloy with "thermal shape memory" properties that allow the material to be ductile at room temperature but attain a prespecified threedimensional configuration when warmed.v' Coating metallic stents with cultured human endothelial cells may accelerate the reendothelialization process after deployment.i" Alternatives to metal alloys are also being considered, including polymeric compounds that may be less thrombogenic, may dissolve after a specified period, and could potentially provide a vehicle for localized delivery of drugs into the vessel wall. Like nitinol, some polymeric materials may have differing configurations at different temperatures. Also under consideration are combinations of metallic and polymeric materials that could provide the mechanical strength and conformability of metallic alloys plus the porosity and low thrombogenicity of polymeric compounds.
CONCLUSION Our initial experience with the flexible metallic coil (Gianturco-Roubin) coronary stent shows it to be a promising device for the treatment of acute and threatened coronary closure after catheter-based intervention. Use of a coronary stent may decrease morbidity in some patients. Metallic coil stents may be safely placed in restenotic lesions and also in primary atherosclerotic lesions; differences in the long-term outcome between these two groups remain uncertain. The ability to place stents presages the ability to implant endovascular prosthetic devices for local administration of drugs, which may decrease the frequency of thrombosis, improve reendothelialization or vascular heal-
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ing after intervention, and diminish the occurrence of restenosis. The long-term outcome of patients in whom intravascular stents have been placed remains to be determined.
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