Cutting Balloon Angioplasty for Underexpanded Stent Deployed Through Struts of Previously Implanted Stent

Since randomized studies showed a lower restenosis rate in focal coronary artery lesions with coronary stenting compared to conventional balloon angioplasty,1 indications for stenting expanded to complex lesions such as bifurcation and ostial lesions.2 When stenting a bifurcation, a stent may cover the ostium of the branch. Balloon inflation through stent struts may sometimes be necessary in order to treat a compromised sidebranch3 or a new lesion at the ostium during follow-up. However, stent struts may prevent full balloon expansion at the ostium of a sidebranch, resulting in residual ostial stenosis, which is a risk of restenosis.4,5 The Cutting Balloon (Interventional Technologies, San Diego, California) has been used to treat resistant lesions and in-stent restenosis.6–9 This balloon catheter has 3–4 microblades longitudinally attached to the balloon, which create a focused force to dilate a resistant lesion. This case report describes Cutting Balloon angioplasty for an underexpanded stent deployed through the struts of a previously implanted stent. Case Report. A 41-year-old female status post coronary artery bypass surgery, with previous stent placement using a 7 cell NIR stent (Boston Scientific/Scimed, Inc., Maple Grove, Minnesota) at the ostium of the left anterior descending (LAD) coronary artery, was admitted due to exertional angina. Coronary angiography revealed a 70% stenosis from the distal left main to the proximal left circumflex (LCX) artery and a 99% stenosis at the ostium of the LAD (Figure 1A). The right coronary artery (RCA) was totally occluded. The saphenous vein grafts to the diagonal artery and the right postero-descending artery as well as the left internal mammary artery to the LAD were patent. The patient was referred for coronary angioplasty. After a 7 French (Fr) VL 3.5 guiding catheter (Boston Scientific/Scimed, Inc.) was positioned at the left main ostium, a 0.014´´ Balance Middle Weight guidewire (Guidant Corporation, Temecula, California) was advanced into the distal LCX. Pre-intervention intravascular ultrasound (IVUS) imaging using a 30 MHz, 3.2 Fr UltraCross catheter (Boston Scientific/Scimed, Inc.) was tried, but the IVUS catheter would not cross the LCX ostium. Balloon angioplasty was performed using a 2.5 mm Adante balloon catheter (Boston Scientific/Scimed, Inc.) inflated to 12 atm. The IVUS catheter then crossed the lesion. IVUS image demonstrated a small lumen [cross-sectional area (CSA), 2.2 mm2] at the ostium where soft plaque was observed. The struts of the stent previously deployed at the LAD ostium jailed the LCX ostium (Figure 2A). A 13 mm Tristar stent (Guidant Corporation) premounted on a 3.0 mm balloon catheter was advanced through the struts of the NIR stent at the ostium of the LAD. Using an inflation pressure of 16 atm, it was deployed at the ostium of the LCX, but the balloon catheter would not fully expand. Additional balloon angioplasty using a 3.25 mm Solaris balloon catheter (Guidant Corporation) was performed. However, despite 25 atm inflation pressure, some indentation of the balloon catheter at the LCX ostium was observed (Figure 1B). Although angiography showed a good result (Figure 1C), IVUS imaging demonstrated stent underexpansion at the LCX ostium (lumen CSA, 3.9 mm2) (Figures 2B and 2C), probably due to the struts of the stent at the LAD ostium. Further balloon angioplasty was not performed because a 3.25 mm balloon catheter had been inflated up to 25 atm. Following stent implantation, aspirin (325 mg/day) and clopidogrel (75 mg/day) were started for 4 weeks. The patient’s hospital course was uneventful. Four months later, the patient was readmitted due to exertional angina. Angiography demonstrated in-stent restenosis of 70% severity at the LCX ostium (Figure 1D). Balloon angioplasty using a 3.5 mm Cutting Balloon inflated to 8 atm was performed and full balloon expansion was observed (Figure 1E). Additional balloon inflation using a 3.5 mm Solaris balloon catheter at 16 atm was performed with full balloon expansion. The final angiography demonstrated an excellent result (Figure 1F). Discussion. The indications of the type of lesions that may be approached with coronary stents have expanded significantly to include more complex lesion subsets such as bifurcation and ostial lesions.2 When a bifurcation lesion is treated, the sidebranch may undergo balloon angioplasty or stent deployment through stent struts after placing a stent in the main vessel (true bifurcation lesion). This situation may also be encountered when a stent is placed in a main vessel and it causes an obstruction of a sidebranch by so-called “plaque shifting”.10,11 Furthermore, a new lesion at the ostium of the sidebranch may develop during follow-up. When stenting a bifurcation lesion, a stent may cover the ostium of the sidebranch. The stent deployed across a sidebranch results in partial blockade of its ostium by stent struts, restricting access to the sidebranch (stent jail).3 Although a guidewire and balloon catheter may cross the stent struts into a sidebranch, full balloon expansion may be impeded,4 which results in residual stenosis. The design and structure of the stent in the main vessel can play a major role in influencing expansion of stent struts, which affects completeness of balloon inflation at the ostium of a sidebranch.12,13 An in vitro study12 showed limited expansion of the struts of the Palmaz-Schatz stent (Johnson & Johnson Interventional Systems, Warren, New Jersey) and the NIR stent after balloon inflation through stent struts. In contrast, the Multi-Link stent (Guidant Corporation) had a larger lumen after balloon inflation through stent struts. Another in vitro study13 evaluated changes in the lumen size surrounded by stent struts after balloon inflation through stent struts at 14 atm. The beStent (Medtronic AVE, Santa Rosa, California) and the NIR stent, which have smaller slots or cells, had little change in diameter of the lumen surrounded by stent struts with increasing balloon size (2.5–3.5 mm balloon catheter) until rupture and marked slot or cell distortion occurred (4.0 mm balloon catheter). For the Crown stent (Johnson & Johnson Interventional Systems) and the Multi-Link stent, which have larger slots or cells, increasing balloon size straightened and displaced the undulating margins of the slots or cells, making them larger and more circular. The GFX stent (Medtronic AVE), which has a linked zigzag ring design, had a side-lumen enlargement due to displacement and separation of individual circumferential ring elements. They are easily separated because each is linked to the next by a single weld. In the present case, limited stent strut expansion capability of the NIR stent might be the reason for limited balloon expansion and the small final lumen CSA after stenting a lesion at the LCX ostium through the stent struts of the stent deployed at the LAD ostium. This was reinforced by the IVUS finding of the presence of soft plaque without calcification at the LCX ostium, which ordinarily would yield to only moderate inflation pressure. Previous case reports14–16 showed techniques to treat resistant lesions, such as the hugging balloon inflation technique,14 which involves the simultaneous inflation of two balloon catheters in a lesion. However, it requires crossing the lesion with two guidewires and two balloon catheters. Although it may be possible to advance two guidewires through the same cell surrounded by stent struts using a transfer catheter, it might be difficult to cross two balloon catheters because of limited space. The buddy wire technique is also used to treat resistant lesions.15,16 With this approach, a guidewire is passed alongside a conventional balloon catheter. When the balloon is inflated at high pressure, the adjacent wire creates a focused force like the microblade of a Cutting Balloon. It is important that the parallel guidewire is in front of a rigid atherosclerotic plaque. However, because the cell of the stent has a complex shape (Figure 2C), the parallel guidewire might be out of position. Rotational atherectomy has been shown to be useful to treat resistant lesions.17 However, it would not be recommended in the present case because it would have deformed the stent.18 The Cutting Balloon has been used to treat resistant lesions and in-stent restenosis.6–9 This catheter has 3–4 atherotomes (microsurgical blades) longitudinally attached to the balloon, with which balloon inflation induces cutting or incision of the atherosclerotic plaque. These microtomes, approximately 0.25 mm in height, are 3–5 times sharper than conventional surgical blades. The microtome edge initiates an indentation into the plaque, after which the shear force applied by the balloon inflation propagates the crack. Depending on balloon size, the cutting force at the blade edge is enhanced 200,000–400,000 times.19 Previous studies6,7 demonstrated successful Cutting Balloon angioplasty in resistant lesions with and without calcification that had been undilatable with conventional balloon catheters inflated at high pressure. The microblades of the Cutting Balloon might have created a focused force to cut stent struts in the present case. We performed an in vitro experiment to evaluate the capability of expanding a cell of the NIR stent by inflation of a conventional balloon catheter and Cutting Balloon through the struts. After predilatation with a 3.0 mm Adante balloon catheter inflated to 14 atm, a 3.5 mm Cutting Balloon and a 3.5 mm conventional balloon catheter (POWERSAIL) were inflated through the struts of a 7-cell NIR stent expanded by the 3.0 mm balloon catheter of the stent delivery system inflated to 14 atm. The conventional balloon catheter was not fully expanded up to 18 atm (rated burst pressure) and limited expansion of the NIR stent cell was observed (Figure 3A). Rupture of the NIR stent cell occurred at 19 atm (Figure 3B). On the other hand, the Cutting Balloon fully expanded at 8 atm and a large lumen with cell rupture was observed (Figure 3C). In the present study, a 3.5 mm conventional balloon catheter was not used. However, inflation of a larger balloon at high pressure (> 18 atm) has a risk of balloon rupture, vessel perforation and dissection.20 In addition, in situ balloon expansion could be limited by the vessel wall as well. The Cutting Balloon is gaining popularity for the treatment of in-stent restenosis.21 Previous IVUS studies22 have demonstrated that coronary stenting eliminates negative arterial remodeling, and thus, intimal hyperplasia is solely responsible for in-stent restenosis. However, IVUS imaging sometimes reveals in-stent restenosis due predominantly to stent underexpansion (“pseudo” in-stent restenosis).23 In the present case, the “underexpanded” cell was free from the vessel wall. On the other hand, stent underexpansion is usually observed in rigid fibrocalcified lesions.23 However, it might be possible that the Cutting Balloon cut both stent strut and fibrocalcified plaque behind the strut to obtain further stent expansion in this type of lesion. Because of the microblades, the Cutting Balloon is less flexible and has a larger profile than conventional balloon catheters, which makes delivery failure likely to be more frequent with the Cutting Balloon compared to conventional balloon catheters. Thus, although predilatation with a conventional balloon catheter results in incomplete expansion of the stent struts, it may be useful to facilitate the Cutting Balloon across the lesion. Because there is a risk of entrapment of the balloon catheter when withdrawing it through stent struts,24 the operator should be careful not to advance the entire balloon of the Cutting Balloon beyond the stent struts in the main vessel. This case report demonstrates underexpansion of the stent deployed through the struts of a previously implanted stent. Because the design and structure of the stent in the main vessel can play a major role in influencing expansion of stent struts, careful stent selection is warranted when treating a lesion with a sidebranch. The Cutting Balloon may be useful to treat this kind of lesion.

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