Cutting Balloon for Bifurcation Lesions Jailed by NIR Stent

With the increasing use of stents, sidebranch compromise after stent deployment in the parent vessel has been a matter of concern. In such bifurcation lesions, it is hard to obtain initial success. Moreover, they carry a high risk of restenosis. Although various techniques have been proposed for jailed bifurcation lesions, one simple approach is balloon angioplasty of the sidebranch. However, the lumen size of the sidebranch after balloon angioplasty varies among different stent designs. While the NIR stent is frequently used, it is the most difficult stent strut through which to dilate because of the smaller closed cell design. Kinoshita et al. reported that the minimum lumen diameter was 1.7 mm after balloon angioplasty through the NIR stent strut.¹ Rotational atherectomy may be another approach, but there are concerns about its safety.² The cutting balloon (CB) is a non-compliant balloon with metal blades on its surface that has been shown to be effective in the treatment of highly resistant calcified lesions.^3,4 The present case illustrates the successful use of a CB to treat a vessel jailed by a NIR stent, and this study evaluates the feasibility and effectiveness of CB angioplasty in such lesions compared to conventional balloon angioplasty. Case Report. A 73-year-old male patient was admitted to our hospital for worsening effort angina. Six months prior to this admission, he had undergone coronary angioplasty of the left circumflex coronary artery (LCX). A 3.0 x 12 mm, seven-cell NIR stent (Boston Scientific, Maple Grove, Minn.) was implanted in the first obtuse marginal artery. However, the proximal portion of the stent was mistakenly placed with protrusion into the main vessel. At this time, coronary angiography showed 90% stenosis of the proximal LCX, just distal to the NIR stent (Fig. 1). The lesion was crossed with a 0.014´´ Hi-torque Balance guidewire (Guidant Corp., Temecula, Calif.). A 2.5 mm balloon was passed without resistance and inflated up to 12 atmospheres (atm). A 3.5 x 15 mm Multi-Link stent (Guidant) was then implanted at 12 atm, but marked indentation was noted at the NIR stent strut (Fig. 2). Subsequent dilatation using a 3.25 mm Maxxum balloon (Boston Scientific) was not successful because the balloon ruptured at 10 atm (Fig. 3). Next, a 3.0 mm Quantum Monorail balloon (Boston Scientific) was inflated at 20 atm. However, the indentation of the balloon persisted. We decided to use a CB (IVT, San Diego, Calif.), because the balloon was noncompliant and the blades on the balloon were expected to prevent balloon rupture. A 3.25 mm CB was therefore introduced and the lesion was dilated at 15 atm. At this time, the indentation of the balloon completely disappeared (Fig. 4). Following deflation, the CB was pulled back and inspected for possible balloon damage. The blades of the CB were slightly distorted, but no fracture was found on the blades. The final angiogram showed excellent results (Fig. 5), and intravascular ultrasound images revealed improved lumen dimensions (Figure 6). The patient had an uneventful recovery and was discharged the following day. A model of bifurcating vessels was made from a flat Plexiglas sheet with 4.0 mm troughs connected to each other at a 45° angle, as previously described (Fig. 7).5 Tubes made from vinyl chloride with a side hole were fixed inside this model. The outer and inner diameters of the tube were 4.0 and 3.5 mm, respectively. The side hole diameter was 3.5 mm. A 3.5 mm, seven-cell NIR stent was implanted at 14 atm in the main vessel, covering the ostium of the sidebranch. A 0.014´´ Hi-torque Balance guidewire was advanced into the sidebranch through the stent strut. At the ostium of the sidebranch, a CB (3.0, 3.5 or 4.0 mm) or conventional balloon (3.0, 3.5 or 4.0 mm Quantum Maverick balloon) was inflated. The inflation pressure was gradually increased up to 18 atm until the indentation in the balloon disappeared. After this step, the stent was removed from the model. The dilated stent struts, representing the ostium of the sidebranch, were photographed en face with a digital camera. The dimensions of the stent struts were measured at 10x magnification with an NIH image (NIH image 1.61, NIH), using a ruler photographed in the same plane for calibration. Mean lumen diameter (average of major and minor diameter) and cross-sectional areas of the stent struts were measured at the ostium of the sidebranch. For each series, results were expressed as means ± standard deviations from three different photographs. For each balloon size, the stent strut dimensions were larger with the CB than with the conventional balloon (Fig. 8). After CB angioplasty, the created lumen became larger in proportion to the increase in balloon size (side lumen diameter was 2.2 mm after use of 3.0 mm CB, 3.2 mm after 3.5 mm CB and 3.6 mm after 4.0 mm CB). In contrast, the size of the conventional balloon had little effect on the lumen dimensions. With all of the conventional balloons and the 3.0 mm CB, balloon, the indentation did not disappear at the maximum inflation pressures. On the other hand, the 3.5 mm and 4.0 mm CBs caused strut rupture at 14 atm and 8 atm, respectively. The ruptured strut was markedly distorted. The sharp ends of the disrupted strut protruded into the sidebranch (Fig. 9). Neither balloon rupture nor fracture of CB blades occurred in this series. However, there was difficulty in retrieving the CBs because the edges of the blades were stuck inside the stent. Discussion. The present report suggests that the CB is effective for treating a bifurcation lesion jailed by a NIR stent. In our in vitro model, the CB created larger side lumen dimensions than a conventional balloon. According to Kinoshita et al., after balloon angioplasty, the dimensions of a sidebranch ostium jailed by a NIR stent were smaller than with a Multi-Link stent. After dilatation with a 3.5 mm balloon at 6 atm, the minimum lumen diameter of the sidebranch ostium was only 1.7 mm with a NIR stent.¹ In effect, the closed cell of the NIR stent strut has to be opened to achieve sufficient lumen dimensions. When 3.5 mm and 4.0 mm CBs were used in our model, the strut ruptured and the lumen was well dilated. Another study by Ormiston et al. showed that the NIR stent strut was destroyed and dilated only when a 4.0 mm conventional balloon was inflated at high pressure (14 atm).⁵ Thus, the created lumen size of the sidebranch seems to be dependent on the balloon size and the inflation pressure. Unfortunately, conventional balloons frequently rupture at such lesions if inflated at high pressure, which can cause critical complications, such as coronary perforation or dissection. Besides, a ruptured balloon tends to become entrapped inside the stent due to incomplete deflation. The CB is a noncompliant balloon with three or four metal blades mounted longitudinally on its surface. A recent case report showed the effectiveness of CB angioplasty through stent struts.⁶ Moreover, other reports referred to the feasibility and safety of CB angioplasty in treating resistant calcified lesions.^3,4 Thus, we assumed that the CB was effective in dilating the rigid strut of a NIR stent. As shown in this report, one benefit of approaching jailed vessels with a CB is its strength to dilate the rigid stent strut. However, the risk of balloon entrapment inside a stent is the major concern when using a CB through the stent struts, as shown by our in vitro experiments. There have been some case reports of CB entrapment during treatment for in-stent restenosis.^7–9 Therefore, the CB should not be regarded as the first choice for this kind of situation. The risk of entrapment seems to be dependent on several factors, such as the angle between a sidebranch and a main vessel, the position of the stent and the stent design (slotted-tube or coil). In the present case, the angle between the two vessels was 90°, but the NIR stent was at the sidebranch. These anatomical factors were likely to make delivery and retrieval of the CB easier. Besides, the CB was advanced a little before withdrawal. It was then pulled back with slight back and forth vibrations, and no resistance was noted. These maneuvers may have unlocked the blade from the stent strut. Based on the merits and demerits of CB angioplasty, our approach to treating bifurcation lesions jailed by a NIR stent is outlined in Table 1. Study limitations. First, the effectiveness of CB angioplasty was evaluated using an in vitro model, which may not have reflected the real situation in this case report, where the angle between the sidebranch and the main vessel was not 45°, but approximately 90°. Second, a Multi-Link stent was implanted before CB angioplasty, which may have protected against balloon damage and facilitated complete balloon dilation. Conclusion. When it is necessary to treat lesions jailed by a NIR stent, a CB should be avoided if possible because of the risk of entrapment. However, the CB could be used as a last resort if carefully performed under surgical back-up.