Stenting the Stent

The most useful attribute of stents is their ability to scaffold the artery, thereby repairing dissections and preventing arterial recoil, with beneficial effects upon the incidence of acute closure1 and restenosis.2 “Coil” stents are less effective in the latter role than “slotted tubes”, cut as either cellular or ring designs, which possess greater radial strength.3 Slotted tube stents are manufactured with parameters of radial strength, percent metal coverage, strut thickness and mesh design which are adequate to support the majority of coronary artery stenoses without imposing too much of a penalty upon flexibility. It follows that there may be a minority of tough lesions in which a single stent provides insufficient radial strength. We aimed to assess the safety and efficacy of “stenting the stent” in such cases. METHODS Patient and lesion selection. We prospectively screened a consecutive series of 500 patients undergoing percutaneous coronary intervention (PCI) by a single operator (JG) in the period 1998–2001. We identified de novo lesions which, after stent deployment, displayed a suboptimal angiographic result. The stents used were all slotted tubes (cellular or ring designs). A suboptimal result was defined as an unacceptable residual stenosis comprising a discrete, unchanging filling defect or an edge dissection despite full and adequate balloon sizing and expansion. Filling defects that changed in appearance, moved within the artery, or were obliterated by high-pressure balloon deployment (as assessed angiographically) were interpreted as thrombus, treated as such and excluded from this study. Magnified digital angiographic images in two orthogonal planes were used to assess the arterial segment. Intravascular ultrasound was not routinely used. Treatment of suboptimal results. Suboptimal lesions were post-dilated with >= 18 atmospheres (atm) of balloon pressure. Complete balloon expansion was required to match the size of the reference segment, with incomplete balloon expansion interpreted as being due to an “undilatable” lesion (which was treated by other techniques and excluded from the study). In cases in which the reference segment enlarged, or in which it had been underestimated in the first place, a larger balloon size for postdilatation was selected. Only the subset of these lesions that displayed a suboptimal appearance after stent deployment despite full balloon and stent expansion comprised the study group. Deployment of a second stent. A second stent was deployed in persistently suboptimal lesions. Again, a slotted tube design was selected to provide maximal radial strength. The size of the implanting balloon was selected to match the diameter of the reference segment. High-pressure dilatation (> 18 atm) was employed in all cases. Adjunctive treatment. Weight-adjusted intravenous heparin was given to maintain the activated clotting time above 250 seconds. Antiplatelet therapy comprised clopidogrel 300 mg (loading dose) followed by 75 mg daily for two weeks, and aspirin 300 mg load followed by 300 mg daily for two weeks and 75 mg daily thereafter. Glycoprotein IIb/IIIa inhibitors were administered for high-risk cases only. Endpoints. The primary endpoint was an optimal final angiographic appearance, with disappearance of the filling defect visible after the first stent deployment. The secondary endpoint was in-hospital and 6-month major adverse cardiac events (MACE, comprising death, myocardial infarction, coronary artery bypass graft surgery, target vessel revascularization and target lesion revascularization). Data sources were hospital records, PCI records, clinic notes and telephone questioning. In cases involving target lesion revascularization, note was made of the position of the restenotic plaque, and in particular whether it was related to the overlapping stent segment. RESULTS Study patients and lesions. In the study period, out of 500 patients undergoing PCI, a total of 18 patients/18 lesions (3.6%) were identified that displayed a persistently suboptimal, post-stent angiographic appearance, not due to thrombus, despite high-pressure post-dilatation with full balloon expansion. The characteristics of the study patients and lesions are displayed in Table 1. Typical examples are shown in Figures 1–3. Immediate and in-hospital results. A second stent was implanted in all 18 segments with 100% success. There were no procedural complications. The final angiogram was judged better than the pre-second-stent angiogram in 17 cases; in the 18th, it was unchanged (as assessed at case review by author JG). There were no untoward procedural or in-hospital complications in 17 patients. In 1 patient, who received an inadvertent air embolism to another vessel during the index procedure, there was persistent, atypical chest pain. Recatheterization on day 4 revealed normal arteries. Long-term results. Mean long-term follow-up was 21 ± 10 months. During that period, there were no deaths or myocardial infarctions, as judged by traditional criteria of >= 2 of classical chest pain, electrocardiographic and enzyme abnormalities. Three patients (17%) required target vessel revascularization, of which 2 (11%) required target lesion revascularization, of which one (5.5%) exhibited restenosis in the “stent-in-stent” segment. In this case, the lesion was ostial. The restenosis was successfully treated with balloon dilatation. Twenty-six months after his index procedure, the patient remains well. DISCUSSION In this study, we found that 3.6% of patients undergoing PCI in a British population had a lesion that appeared suboptimal after stent deployment and thorough post dilatation. Two thirds of these were due to tissue or stent prolapse. These patients were treated with stent deployment to the suboptimal segment (“stenting the stent”) with 100% procedural success, no complications relating to the lesion in hospital, an 11% target lesion revascularization rate and 5.5% recurrence at the site of overlap. A suboptimal appearance in a stent may be due to thrombus formation, prolapse of tissue through the struts or recoil of the lesion and stent together. In the case of tissue or stent prolapse, a mechanical solution is required. Further balloon inflation is usually undertaken, with prolonged or high-pressure deployment, and balloon upsizing if the reference diameter allows. Occasionally, despite these maneuvers, suboptimal appearance persists. Our data suggest that this occurs in a small proportion of cases, despite the use of slotted tube stents (rather than coil designs) and even “added support” slotted tubes (for example, the BiodivYsio Added Support stent manufactured by Biocompatibles), which contain extra strut elements (Figure 4). A logical solution to the problem is the application of additional radial support in the form of a second stent, a technique which we have shown here to be safe and effective. There are precedents for “stenting the stent”. Probably the most common reason is to treat in-stent restenosis, usually after adjunctive therapy with balloon inflation or rotational atherectomy. This is a safe procedure, although it has no special advantages over other techniques in terms of restenosis. Al-Sergani et al. treated 31 patients with 32 procedures for in-stent restenosis with further stent implantation (all Palmaz-Schatz stents; mean deployment pressure, 17 atm; residual stenosis 50%). All of these patients underwent target lesion revascularization.6 Their long-term results were, therefore, modest and probably not superior to other techniques such as cutting balloon deployment. Our recurrence rate was considerably lower than this, and we had no therapeutic options other than “stenting the stent”. Were there any particular features of the lesions featured here that might have predicted the requirement for “stenting the stent”? The incidence of angiographically visible calcification was 9/18 (50%), which is higher than the 15% that is expected in a general population of lesions undergoing PCI.7 The proportion of lesions that were chronic total occlusions (3/18, 17%) was consistent with the 10–20% seen in the general PCI population.8 Three of the 18 (17%) were truly ostial in location, certainly more than expected in the general PCI population, but not statistically significant (Figure 1). A preponderance of bulky, concentric lesions was noticeable in our study population. Deformation of the balloon might signify a potential for tissue prolapse or stent recoil, and consideration might then be given to a debulking technique. IVUS imaging might also assist this decision-making process, but its widespread use would have significant resource implications. In any case, we have shown that it is possible to produce good acute- and long-term results using a pragmatic angiographic assessment, followed by second stent placement, without resorting to these measures. A potential hazard of “stenting the stent” might be thrombus formation in the interstices of the metalwork, some of which may not be in contact with the wall of the artery. Subacute or late thrombosis was not observed in our series, despite using standard oral anti-platelet therapy (a IIb/IIIa inhibitor was only given in one case). “Stenting the stent” should increase the caliber of the artery, encouraging the anticoagulant effect of brisk blood flow and, indeed, we demonstrated no untoward clinical problems during a follow-up period of 21 ± 10 months. Study limitations. The principal weaknesses of this study are the small number of cases, the lack of randomization to an alternate strategy and the rare use of intravascular ultrasound. Nevertheless, this is the first published record of the practice of “stenting the stent” acutely for sound reasons. Conclusion. Where more mechanical support is required, it is safe and effective to “stent the stent”.

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