STENT IMPLANTATION AFTER PTCA: AN OVERVIEW

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1 102 Articles STENT IMPLANTATION AFTER PTCA: AN OVERVIEW JURGEN MEYER,MD AFTER THE INTRACORONARY application of metal stents initially proposed by U. Sigward, a very aggressive anti thrombotic treatment was used. During the last years, however, the anti thrombotic treatment has been completely reevaluated. Currently, the therapy with ticlopedine and aspirin reveals excellent results with little bleeding. The current indications of stent implantation are severe dissections and impending occlusions of the coronary arteries after intracoronary interventions. These bailout applications, in many occasions, are able to keep the vessels open, to stabilize the dangerous situation, and to save bypass surgery. The second indication is insufficient dilatation result with large dissection and intracoronary flap. The third indication is given in patients with recurrent restenosis after previous dilatations. Stents have been implanted in patients with acute myocardial infarction, mechanical opening of the infarct artery, and a high risk of reocclusion. Many approaches to develop special stents, which can deliver substances to the endothelium and the dilated region, are underway. By this, the mechanisms of restenosis may be influenced. Since the first application of intracoronary balloon dilatation (PTCA) by Andreas Gruntzig, in 1977, in Zurich, Switzerland, many improvements of this technique have been achieved. The success rate of intracoronary maneuvers is 90% to 95%. Complicated coronary artery segments in multiple vessels can be reached and treated successfully. Up to now, however, the high restenosis rate after the From the Department of Medicine, Johannes Gutenberg University, Mainz, Germany. Address reprint requests and correspondence to Dr. Meyer: Department of Medicine, Johannes Gutenberg University, Langenbeckstreet I, D Mainz, Germany. procedure and the threat of acute vessel occlusion remain the two major problems. In the early 1980s, intracoronary application of metal stents was proposed by U. Sigward. Because of the high thrombogenicity of the metal stents within the arterial system, a very aggressive anti thrombotic treatment was initially used. During the last decade, however, great advantages have been achieved by a modified treatment. After dilatation of severely calcified, high-grade stenoses (Figure I), the dilated area very often shows broken atheroma with the threat of acute occlusion. Angiography and intravascular ultrasound show severe plaque disruptions. These broken atheromal have a tendency of acute occlusion imd high-grade restenosis within the first weeks. Therefore, the implantation of an intracoronary stent can stabilize the flow, enlarge the vessel lumen, and hopefully prevent the area from restenosis. If the coronary flow reserve (Figure 2) is severely reduced before PTCA, the intracoronary dilatation is able to gain much better perfusi.on. Our studies have shown that by adding intracoronary stents the coronary flow reserve is augmented by another 50%.2 Indications for Intracoronary Stents There are many indications for intracoronary stent placement after interventions (Table I). The placement of stents in cases with threatening vessel occlusion after PTCA has reduced the number of emergency bypass operations. This bailout situation is one of the leading indications for stent placement. Using the guidewire distally to the dilated segment area, one or more stents can be placed via a high-pressure balloon. Also, in cases with severe, longitudinal and spiral dissections, the Journal of the Saudi Hean Association, Vol. 8. No.2, 1996

2 STENTIMPLANTATION 103 Figure I. Dilatation of a proximal, heavily calcified LAD stenosis: (a) high-grade stenosis seen angiographically and with intravascular ultrasound; (b) immediate result after PTCA with apparently good result in angiography, however, there is insufficient result in intravascular ultrasound with broken atheroma and irregular vessel lumen; and (c) optimal result after stent implantation, both angiographically and with intravascular ultrasound. CFR 6 Coronary Flow Reserve Table I. Post procedural use of stenls. 4 2 before PTCA afterptca after stent Figure 2. Improvement of coronary flow reserve after PTCA and after stent implantation. improved flow and the smooth vessel surface improve coronary flow and prevent clot formation. If the dilatation result seems to be suboptimal with more than 50% residual stenosis and focal dissections, the indication for stent placement is actually considered more liberally. Since primary balloon dilatation in acute myocardial infarction becomes more clinically used, stents are additionally implanted to prevent an early vessel occlusion and to improve coronary flow. Primary prevention of restenosis has been a topic of the BENESTENT3 and the STRESS4 studies. These and other studies have shown that, at least, in selected cases the early and follow-up results are in favor of stent placement.5-9 Results of Intracoronary Stents The acute and final results of dilatation plus stent implantation are dependent on several additional parameters such as vessel size, stable vs unstable Journal of the Saudi Hean Association, Vol. 8, No.2, 1996

3 104 MEYER angina, native artery, vein graft, internal mammary artery, age, diabetes, vessel diameter, thrombus formation, configuration and length of the dilated area, and, finally, postprocedural treatment Several comparisons between acute, bailout stent placements vs elective stent implantations have shown major differences (Table 2) between the procedures in those two different indications By using different stent types (Palmaz-Schatz vs Gianturco Rubin vs Wiktor vs AVE stents), the results may be different in cases of threatened or acute occlusion. While straight vessels are not problematical with any of them, angulated segments are preferably treated with Wiktor or AVE stents. Larger comparative studies between those systems, however, are not available. Most clinicians seem to develop a certain preference for one or two types of stents. The most important objective is to obtain experience with the different systems in order to learn enough about the specific advantages and drawbacks. After dilatation of stenoses in saphenous vein grafts, high restenosis rates have been reported. By implanting stents into the vein grafts, larger studies have reported quite favorable results.12 Besides the bailout situation, the prevention of restenosis has become the most important indication for stent implantation. After PTCA, in stable angina pectoris, the restenosis rate is 25% to 35%; in unstable angina, 30% to 50%; and after the opening of total occlusions, about 50%. Two randomized trials (BENESTENT Studyl3 and STRESS Study4) have been designed and performed to evaluate the merit of primary stent implantation over conventional therapy. The selection criteria for patient inclusion have been rather' strict and specific (Table 3). The patients selected for both studies were ideal candidates. They, however, do not represent the overall cohort of our patients seen daily in the catheterization laboratory. This is also clearly seen in the list of exclusion criteria (Table 4). Both studies show highly significant better results with primary stent implantation than with PTCA alone (Table 5). The rationale for stent implantation in the situation of acute myocardial infarction after primary PTCA is listed in Table 6. Suboptimal PTCA results with TIMI flow less than grade III and stenosis rates of > 70% are suboptimal since dissections, plaque ruptures, Table 2. Comparison of acute vs elective stent implantations. Bailout Elective Subacute. perioperative 8% - 15% 1%-8% occlusions Infarction 5% - 10% 0.5% - 3% CABG 8% - 13% 2% - 7% Death 3% - 4% 2% CABG - coronary artery bypass graft. Table 3. Patient selection in the BENESTENT and STRESS studies. BENESTENT STRESS Single lesion De novo lesions. native arteries Stable angina Single lesion Lesion length < 15 mm Symptomatic patients Lesion length Vessel diameter> 3.0 mm Normal < 15 mm Vessel diameter> 3.0 mm functioning myocardium Suitable for > 70% diameter stenosis CABG CABG - coronary artery bypass graft. Table 4. Exclu.fion criteria in the BENESTENT and STRESS studies. BENESTENT STRESS Thrombotic lesion Contraindication to antiplateletl anticoagulation therapy Ostial lesions Bifurcation lesions Lesion in grafted vessel EF - ejection fraction. Thrombotic lesion Contraindication to antiplateletl anticoagulation therapy Ostiallesionslmain stem stenosis Diffuse disease Vessel tunuosity EF < 400/0 Acute infarction < 7 days thrombi, recoil mechanisms, and spasms may disturb coronary flow, and by this hamper the recovery of the myocardium is in danger. Up to now, there are two major studies (Table 7) to analyze the initial results after stent implantation in acute myocardial infarction. The details are not yet published. The initial results at least show that the stent application in dangerous situations such as after intracoronary maneuvers in acute myocardial infarction may be beneficial for the patients. The rates of success, death, emergency operation, and stent thrombosis are comparable with those in patients with unstable angina. Until the year 1994, the percentage of coronary stent implantations in our university clinic did not exceed 10% (Figure 3). After the positive reports of Journal of the Saudi Heart Association, Yol. 8, No.2, 1996

4 STENT IMPLANTATION 105 Table 5. Stenting for de novo lesions in native coronary arteries (BENESTENT and STRESS studies). BENESTENT (520 pts) STRESS (410 pts) PTCA Stent P PTCA Stent P Clinical event 30% 20% % 19.5% 0.16 Restenosis 32% 22% % 31.6% MLD (mm) Post-stent :I: 0.33 :I: 0.39 :I: 0.47 :I: 0.43 Follow-up :1:0.55 :1:0.64 :1:0.65 :1:0.60 Vascular 13.5% 3.1% % 7.3% 0.14 complications Table 6. Rationale for stent implantation in acute myocardial infarction. Results Early and permanent TIMI-1Il flow TIMII-II flow and restenosis Suboptimal PTCA results because of thrombi, plaques, dissections, recoil or spasms Optimal reperfusion strategy Predictors of reocclusions Consequences: PTCA and/or lysis alone do not eliminate the reasons of flow impairment Table 7. Stent implantation in acute myocardial infarction. French Registry Mainz Study Patients (n) Time to symptom onset < 24h <12h Shock 14.9% 22% Success rate 95% 97% Death (3)4.1% (1)3% Emergency OP (I) 1.3% (2) 6% Stent thrombosis (I) 1.3% (2) 6% Table 9. Risks for acute vessel oce/usion after PTCA and after stent implantation. PTCA Stent implantation Severe lesion Long lesion Type C Branch pointlbend point lesion Thrombus Long lesion Unstable angina Bail Type B/C lesion Thrombus out indication Unstable angina Dissection Table 8. Optimal stent technique. High pressure balloon (14-18 atm) IVUS control Thrombocyte aggregation inhibition (ASS + ticlopidine) No anticoagulation 6- F catheters New stent designs % BENESTENT/STRESS. HIgh pressure Inflation. IVU5-guldance. AntIthrombotlc therapy \f 14 % 34% Transradial approach IVUS - intravascular ultrasound Figure 3. Development of the rate of stent implantations per total PTCA procedures over the period , University of Mainz. Journal of the Saudi Hean Association. Vol. 8. No.2.

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6 STENT IMPLANTATION 107 Table 14. Patient selection for stent implantation. Elective Stenting - Clinical benefit in randomized trials. No general indication ( net gain during follow-up, mm) - Possible indication in high-risk patients (dominant vessel) Threatened/Acute Closure - Proven benefit in observational trials - Liberal use (vessel diameter> 3 mm/> 2.5 mm), avoid time delay Suboptimal PTCA Result - High-risk subgroup for future restenosis - No general indication for stenting - Liberal use in patients with restenosis Saphenous Vein Graft - Promising results in observational trials - Elective stent might be considered Restenosis after PTCA - Probably improved results after stenting - To date, no general indication for elective stenting - Aggressive PTCA aimed at good post-ptca results, Slent in dicated in suboptimal results the BENESTENT and STRESS results, the use of high-pressure inflation, intravascular ultrasound guidance, and optimized anti thrombotic therapy, the numbers have increased significantly. Now, in our institution about one-third of all intracoronary balloon dilatations are directly followed by an intracoronary stent implantation. The improved stent technique (Table 8) has significantly contributed to the beneficial immediate and late results. Because of the specific intracoronary situation, many risks for subacute thrombosis after stent implantation are very similar to those risks for acute closure after PTCA (Table 9). Long and complicated lesions, especially in patients with unstable angina and thrombus formations, are the major sources of complications and acute vessel occlusions. Despite the use of high-pressure balloons, the struts of the stents are not always in close contact to the vessel wall.2,12-14 In particular, severely dissected, ulcerated plaque formations may show a free central part of the lumen and these areas are also not covered by the stent (Figure 4). Some of the struts are closely attached to the endothelium, while others may be within the free lumen and even be angulated. It has been shown (Table 10) that with the use of high-inflation pressures during stent implantation, not only the balloon size but also the eccentricity index, the minimal lumen diameter, the echofree space, and the number of oblique struts can be improved.14,15 These improvements have led to much better immediate and late results. Therefore, balloon pressures currently between 14 and 18 atm are mostly used. In normal cases, only coronary arteriography is used for the control of stent placement. In some cases, however, there are questions and doubts on whether the stent is really located at the correct place. We therefore use intracoronary ultrasound in those cases (Figure 1) to control the placement and to evaluate the necessity of placing further stents. The ultrasound criteria for successful stent implantation are: (1) symmetry of the area; (2) minimal lumen diameter> 3.0 mm; (3) no echofree space between stent and vessel; and (4) no uncovered dissections. If these criteria are met, the immediate and fmal results are much better than without them Over many years, very aggressive anti thrombotic treatment strategies including heparin, warfarin, aspirin, persantin, and ticlopedine have been used. These regimens, in many cases, have led to severe bleedings at the puncture site and often to surgical vessel repair. The normal stay in the hospital was extended from 7 to 10 days. Over the last years, however, several studies have shown that such an aggressive anti thrombotic treatment is no longer necessary. 12,14,16,17 We therefore now follow a simple treatment regime for thrombosis prophylaxis after stent implantation. This treatment consists of: (1) heparin, WOO to 1200 ulh for 24 h; (2) ticlopidine, 2 X 250 mg for 4 weeks; and (3) acetylsalicylic acid, 300 mg for 4 weeks and then 100 mg for 6 months. The treatment may even be restricted to aspirin only.l7 With this treatment, patients can be discharged within four days. The final results after six months are excellent. Conclusion Stent implantation is not always suitable..md indicated. Even if the list of indications and contraindications may vary from institution to institution and from operator to operator, there are some items to be considered. In special situations, the primary and late results after stent implantation are less favorable (Table 11). Despite the Journal of the Saudi Hean Association. Vol. 8. No.2, 1996

7 108 MEYER improvements in stent technology and thrombosis prophylaxis, there are still some problems and skepticism toward stent implantation (Table 12). Since the field of intracoronary interventions is expanding very rapidly, the need for better intracoronary stents is quite obvious. Therefore, many institutions try to improve the stents, the technique for their application, and the postinterventi on treatment to develop better outcome for patients (Table 13). The main areas for further studies are prevention of thrombosis and restenosis. Restenosis still is the major problem, not only after every intracoronary intervention but also after stent implantation. Actually, there are many points of interest and consideration. It is not only important to select the most suitable stents but also to develop an optimal technique for their implantation. The most important consideration is the proper selection of patients who are suitable for this new and invasive procedure (Table 14). The ongoing scientific studies and developments give hope that solutions for the still existing problems will be at hand within the very near future. References I. Falk E, Shah PK, Fuster V. Coronary plaque disruption. Circulation 1995;92: Ge 1, Erbel R, Zamorano 1, et al. Improvement of coronary morphology and blood flow after stenting. Int 1 Cardiol Imaging 1995;11: Serruys PW, de laegere 1, Kiemeneis F, et al. A comparison of balloon expandable stent implantation with balloon angioplasty in patients with coronary anery disease. N Engl 1 Med 1994;331 : Fischman DL, Leon MB, Bairn D. et al. A randomized comparison of coronary stent placement and balloon angioplasty in the treatment of coronary artery disease. N Engll Med 1994;331: Goy 11. Eeckhout E, Stauffer lc, et al. Emergency endoluminal stenting for abrupt vessel closure following coronary angioplasty: a randomized comparison of the Wiktor and Palmaz-Schatz stents. Cathet Cardiovasc Diagn 1995;34: Ikari y, Hara K, Tamura T. et al. Luminal loss and site of restenosis after Palmaz-Schatz coronary stent implantation. Am 1 CardioI1995;76: Ozaki y, Keane D. Ruygrok p, et al. Acute clinical and angiographic results with the new AVE micro coronary stent in bail out management. Am 1 Cardiol 1995;76: Stauffer lc, Eeckhout E, Vogt P, et al. Stand-by versus stent-by during percutaneous transluminal coronary angioplasty. Am Heanl 1995;130: Foley lb, White 1, Teefy p, et ai. Late angiographic follow-up after Palmaz-Schatz stent implantation. Am 1 Cardiol 1995;76: Dussaillant GR, Mintz GS. Pichard AD, et al. Small stent size and intimal hyperplasia contribute to restenosis: a volumetric intravascular ultrasound analysis. 1 Am Coli Cardioll995;26: II. Liu MW, Voorhees WD III, Agrawal S. et al. Stratification of the risk of thrombosis after intracoronary stenting for threatened or acute closure complicating coronary balloon angioplasty: a Cook registry study. Am Hean ;130: Wong SC, Bairn DS. Schatz RA. et al. Immediate results and late outcomes after stent implantation in saphenous vein graft lesions: the multicenter US Palmaz-Schatz stent experience. The Palmaz Schatz Stent Study Group. 1 Am Coli Cardiol 1995;26: Mintz GS, Griffm 1. Chuang YC, et al. Reproducibility of the intravascular ultrasound assessment of stent implantation in saphenous vein grafts. Am 1 CardioI1995;75: Colombo A. Hall P. Nakamura S, et al. Intracoronary stenting without anticoagulation accomplished with intravascular ultrasound guidance. Circulation 1995;91: Gorge G. Haude M, Ge 1, et al. Intravascular ultrasound after low and high inflation pressure coronary anery stent implantation. 1 Am Coli Cardiol 1995;26: van Belle E. McFadden EP. Lablanche 1M, et al. Two-pronged anti platelet therapy with aspirin and ticlopidine without systemic anticoagulation: an alternative therapeutic strategy after bail out stent implantation. Coron Anery Dis 1995;6: Hall P, Nakamura S. Maiello L, et al. A randomized comparison of combined ticlopidine and a5fjir!n therapy versus aspirin therapy alone after successful intravascular ultrasound-guided stent implantation. Circulation 1996;93: Journal of the Saudi Hean Association. Yol. 8. No