Acute Angiographic and Clinical Results of the NIR w/SOX Stent
- Volume 14 - Issue 1 - January, 2002
- Posted on: 8/1/08
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Lower restenosis rates were shown in selected lesions with the first-generation Palmaz-Schatz stent when compared to conventional balloon angioplasty.1 However, because the Palmaz-Schatz stent and its delivery system were rigid, stent delivery failure was not uncommon.2 The introduction of the more flexible second-generation stents have simplified stent delivery. However, stent delivery failure remains a problem in complex lesions, especially in severely calcified or tortuous vessels.3,4 Recently, the NIR w/SOX stent (Boston Scientific/Scimed, Inc., Maple Grove, Minnesota), designed to improve stent delivery, was introduced to the market (Figure 1). The present study evaluated acute angiographic and clinical results of the NIR w/SOX stent.
Study patients and stenting procedure. Between March 2000 and May 2000, a total of 102 lesions in 88 patients underwent stenting with the NIR w/SOX stent at Lenox Hill Heart and Vascular Institute in New York. All procedures were performed after informed consent was obtained. All patients underwent stenting according to current guidelines. The NIR w/SOX stent was selected at the operator’s discretion, especially in the lesions that had a high probability of difficult stent delivery. Prior to stent implantation, the patient was given aspirin (325 mg) and clopidogrel (300 mg). Following stent implantation, aspirin (325 mg/day) and clopidogrel (75 mg/day) were started for 4 weeks.
Definitions of procedural outcomes. Procedural success was defined as successful NIR w/SOX stent delivery and a final angiographic residual diameter stenosis of < 30% by quantitative analysis without a major complication (death, Q-wave myocardial infarction or coronary artery bypass surgery) during the hospitalization. Q-wave myocardial infarction was documented by the presence of new Q-waves of at least 0.04 seconds duration and a creatine kinase level or MB fraction at least twice the upper limit of normal. Acute thrombotic events were defined as angiographically documented occlusion with TIMI grade 0 or 1 flow at the stent site occurring within 24 hours of the stent procedure. Subacute thrombotic events were angiographically documented occlusions with TIMI grade 0 or 1 flow at the stent site occurring beyond 24 hours and within the first month of the stent procedure. One month clinical follow-up was performed by either telephone contact or office visit. The occurrence of major adverse cardiac events was recorded, including death (all-causes), Q-wave myocardial infarction and target lesion revascularization.
Angiographic analysis. All cineangiograms were analyzed using computer-assisted, automated edge detection algorithm (QCA-CMS, MEDIS, Leiden, The Netherlands). Standard qualitative and quantitative definitions and measurements were used. The outer diameter of the contrast-filled catheter as the calibration and the minimal lumen diameter (MLD) were obtained from the single “worst” view. Data were expressed as numbers/percentages or mean values ± standard deviation.
Baseline characteristics. The clinical patient characteristics are shown in Table 1. Overall, the study group represented a high-risk cohort. More than half of the patients presented with unstable angina, 44% had a previous myocardial infarction, and 72% had multivessel coronary artery disease. The incidence of diabetic mellitus was 33%. A history of coronary bypass surgery was observed in 28% of the patients. Glycoprotein IIb/IIIa inhibitor was used in almost half of the patients.
Angiographic and procedural characteristics are presented in Table 2. Stenting was performed electively (91%) or due to suboptimal result (9%). Most of the lesions had the modified American Heart Association/American College of Cardiology lesion type B2 or C. Moderate or severe angiographic calcification was observed in 29% of the lesions.
The long stent (25 mm or 32 mm) was used in 25% of the lesions. Rotational atherectomy prior to stenting was performed in 5 lesions. Multiple stents was used in 31 lesions. In 8 lesions, additional stenting was performed to cover an edge dissection after the NIR w/SOX stent implantation. Final balloon/vessel ratio was 1.14 ± 0.11. Maximal inflation pressure was 15.7 ± 2.8 atmospheres.
Table 3 shows the results of quantitative angiographic analysis. The reference vessel diameter was 2.97 ± 0.50 mm. Lesion length was 16.2 ± 6.5 mm; 34% of the lesions were long lesions (lesion length > 15 mm). The MLD increased from 0.68 ± 0.45 mm to 3.07 ± 0.50 mm.
Procedural outcomes. The procedural outcomes are shown in Table 4. Delivery failure of the NIR w/SOX stent was observed in 4 (four 16 mm stents and one 25 mm stent; in one lesion, neither the 16 mm or the 25 mm stent could be delivered) of 102 lesions (3.9%). Of these, one occurred in the lesion at the distal anastomosis of the sequential saphenous vein graft with a tortuous course to the obtuse marginal branch and the right coronary artery. An AVE S670 stent was successfully delivered in this lesion. Another was observed in a long right coronary artery lesion with severe calcification. The NIR w/SOX stent and several other stents (Tristar stent, AVE S670 stent, Radius stent, BX velocity stent) were tried after predilatation, but none of them successfully crossed the lesion. The procedure was unsuccessful and the patient underwent coronary artery bypass surgery 3 days later. In the third case (Figure 2), stent delivery was performed after rotational atherectomy and balloon angioplasty in severely calcified tandem lesions of the proximal left circumflex artery that had a sharp angulation to the left main. The stent became lodged at the lesion site. Stent dislodgement from the delivery balloon catheter occurred when attempting withdrawal of the stent. It was successfully retrieved by the goose neck microsnare (Microvena, White Bear Lake, Minnesota). Because angiography after conventional balloon angioplasty demonstrated optimal balloon result, no further treatment was attempted. In the fourth case, stent delivery following rotational atherectomy resulted in unsuccessful delivery in a diffusely calcified lesion in the mid-right coronary artery. It was treated by conventional balloon angioplasty without stenting. On the other hand, in 7 of 9 lesions when other stents failed (4 AVE S670 stents, 3 Tristar stents and 1 Minicrown stent; in one lesion neither the Tristar stent nor the AVE S670 stent could be delivered), the NIR w/SOX stent was successfully delivered without changing the guiding catheter and/or guidewire (Figure 3).
Angiographic success was observed in all except one lesion where the NIR w/SOX stents could not be delivered. There were no procedural myocardial infarctions or deaths. In one case described above, procedural coronary bypass surgery was performed. There was no abrupt closure or subacute stent thrombosis. The major adverse cardiac event rate at 30 days was 1.1%.
The NIR stent has a continuous uniform muticellular design and was designed specifically to provide longitudinal flexibility and trackability during deployment, while maintaining high radial support and stent conformation to the vessel wall after implantation.5 Previous studies3,4,6–9 demonstrated high procedural success rates of 90–98% with the original NIR stent. In this study, despite unfavorable lesion characteristics, the NIR w/SOX stent achieved high angiographic success and low complication rates.
The NIR w/SOX stent, which is the next generation of the original NIR stent, was designed to offer enhanced stent crossability by an edge protection system and center-out deployment. The proprietary SOX edge protection system is a sheath-like sleeve providing seamless protection at the both ends of the stent (Figure 1). It enables us to: 1) efficiently cross and deliver the stent by preventing stent flaring; 2) reduce the potential of vessel trauma due to stent flaring; and 3) confidently retract the undeployed stent system into the guiding catheter when necessary. Center-out deployment was designed to: 1) eliminate “dog-boning” during deployment; and 2) maximize MLD by focusing balloon pressure at the center of the stent.
A number of second-generation stents have been developed with innovative designs that impact enhanced longitudinal flexibility combined with excellent radial strength.3,4,6–10 Although these new stents have significantly increased the delivery success rate in challenging coronary anatomy, severe tortuosity, rigidity and calcification of coronary arteries combined with insufficient guiding catheter back-up may still prevent successful stent delivery into the target vessel. Failure of stent deployment may lead to stent embolization during withdrawal.11 Furthermore, inability to stent a lesion may leave suboptimal angiographic results and severe dissections untreated, increasing the risk of abrupt coronary occlusion. Previous studies2 showed high in-hospital complication rates when stent delivery was unsuccessful, especially in bail-out cases. In the present study, the rate of stent delivery failure was not different from those of the original NIR stent (1.0–5.9%).3,4,6–9 However, the lesions treated with the NIR w/SOX stent represented a highly selected group. The lesion characteristics were worse compared to the previous studies.3,4,6–9 On the other hand, it was remarkable that the NIR w/SOX stents were successfully delivered in 7 of 9 lesions when other kinds of stents (AVE S670 stent, Tristar stent, and Minicrown stent) failed to deliver.
The dislodgement of the stent from the balloon catheter and subsequent stent embolization during withdrawal of the stent after delivery failure is an important issue.11 Stent dislodgement was observed in one case in which the stent was lodged in a severely calcified lesion. The edge protection system of the NIR w/SOX stent may prevent stent dislodgement by the edge of the guiding catheter when it is withdrawn into the guiding catheter.11 However, it might not be enough to prevent this complication when the stent lodged in a complex lesion is withdrawn.
During high-pressure deployment of stents, the protrusion of the balloon beyond the edges of the stent with hyperexpansion of these balloon ends (so-called “dog-boning”) could cause shearing at the metal/plaque interface, resulting in a dissection at the edge of the stent. The center-out deployment system of this stent was expected to reduce the rate of this complication. In the present study, the rate of additional stenting by edge dissection after stenting with the NIR w/SOX stent was similar to those shown in previous studies.12,13 An intravascular ultrasound study14 showed that edge dissection was observed where there was much atheromatous plaque burden. Because the NIR w/SOX stents were used in lesions with unfavorable characteristics such as diffuse narrowing, a dissection might be observed at the stent edge with much atheromatous plaque burden, offsetting the benefit of center-out deployment. However, it may not totally eliminate this problem.