Mechanical distortion of a stent, even after successful implantation, may occur as a result of further coronary intervention such as balloon inflation of side branches through the stent struts, dilatation over a guidewire outside the stented lumen and the entrapment of guidewires, balloons, burrs or other devices. Recently, stent rupture, secondary to material fatigue, has been added to the list of incidental stent mechanical complications. We report a case of a successfully deployed stent that, after entanglement with another stent, underwent extreme distortion and elongation up to three-fold its original length. This unusual complication was diagnosed using noninvasive imaging, with successful retrieval of both stents.

Case report. A 71-year-old male with a history of hypertension, dyslipidemia, insulin-independent diabetes and a dual-chamber pacemaker implanted for third-degree atrioventricular block, was admitted with a diagnosis of acute coronary syndrome. His physical examination at the time of presentation was unremarkable. His electrocardiogram showed a paced rhythm and his cardiac enzyme was elevated with a peak CPK of 434 mg/dl. He subsequently underwent coronary angiography, which showed no significant disease in the left main stem, left anterior descending or circumflex arteries. The right coronary artery (RCA), which was tortuous and mildly calcified, displayed 2 severe lesions (Figure 1A) in the proximal and mid segments. The proximal stenosis, which was about 35 mm in length, extended from the ostium to the proximal mid segment of the RCA. The second stenosis, which was separated from the proximal stenosis by a nondiseased segment of approximately 20 mm in length, was short (10 mm) and focal. The patient’s overall left ventricular function was preserved, with evidence of mild inferior hypokinesia.
The patient was scheduled for percutaneous coronary revascularization of the 2 lesions in the RCA. A High-Torque Balance Middleweight Universal^® guidewire (Abbott Vascular, Abbott Park, Illinois) was manipulated and positioned distally in the RCA. Both lesions were predilated. A 2.5 x 12 mm Driver^® stent (Medtronic, Inc., Minneapolis, Minnesota) was implanted successfully in the distal lesion. A second 2.5 x 32 mm Taxus Liberté^® stent (Boston Scientific Corp., Natick, Massachusetts) was positioned over the proximal lesion and deployed at 16 atm. However, the stent failed to cover the distal segment of the lesion (Figure 1B). Therefore, a second Taxus stent (2.5 x 12 mm) was advanced so as to be positioned distally, but failed to advance through the proximal stent, even after performing high-pressure (20 atm) balloon dilatation. This stent was withdrawn and the same maneuver was attempted with a 2.5 x 12 mm Driver stent, which was also unable to progress through the long Taxus stent. However, while the Driver stent was being withdrawn, a strong resistance was felt. In spite of careful maneuvering, the stent appeared to slip off the balloon. Note the guidewire had always been in the distal RCA throughout the procedure. Fluoroscopic examination did not show the stent in the proximal RCA segment. A decision was then made to remove the guiding catheter and the guidewire from the patient as a single unit. The devices were subjected to careful examination and it became evident that the missing stent was not inside the guiding catheter. The guidewire was noted to be completely intact, without rupture of its tip. A repeat RCA angiography was performed and revealed a patent vessel with irregular borders (Figure 1C) in the proximal stented segment. Fluoroscopic examination showed a faint image with flag-like movement in the ascending aorta attached to a linear radiopaque structure (Figure 2A) in the right coronary ostium. The procedure was therefore terminated and noninvasive imaging, including a transesophageal echocardiography (TEE) and computed tomographic (CT) scan, was arranged for further clarification of the clinical situation. It should be noted that the patient remained asymptomatic on enoxaparin, tirofiban and clopidogrel treatment throughout these diagnostic tests.

The patient underwent both TEE and 64-multislice computed tomography (MSCT). The TEE (Figure 2B) showed that there was a dense, linear, mobile structure present in the ascending aorta, while the MSCT scan (Figure 2C) showed that the stent implanted in the proximal RCA was irregular in structure, underdeployed and elongated. In addition, the stent was found to cover only 15 mm of the proximal RCA, while the remaining part of it was floating freely in the aorta. The proximal part of the structure seemed thicker than the rest of it, and the interpretation of these images was that the original stent had been distorted and elongated due to the attachment and traction of the missing stent during withdrawal.
On the same day, the patient was taken back to the catheterization laboratory for retrieval of the missing stent and completion of the RCA stenting procedure. Through a 7 Fr introducer in the right femoral artery, a 15 mm snare loop catheter (Gooseneck Snare, Microvena Corp., White Bear Lake, Minnesota) was advanced to the aortic root and guided by fluoroscopy to catch the stent. This was performed successfully without complications. Figure 3 shows the retrieved material in which the missing Driver stent was attached to the Taxus stent, with the Taxus stent elongated almost three times its original length, from 32 mm to 95 mm. The 12 mm Driver stent was not elongated and its structure appeared to remain intact. After removal of the 2 entangled stents, 3 Driver 2.5 x 12 mm stents were implanted successfully in the proximal RCA. The final result is shown in Figure 4. Post procedure, the patient’s clinical course was uneventful, and he was subsequently discharged 2 days later on dual antiplatelet therapy. At 3- month clinical follow up, the patient continued to be asymptomatic.

Discussion. This case illustrates three different mechanical complications related to coronary stents:
1) Entrapment of a stent with another stent. This is a very unusual complication, which is more prone to occur with coil stent platforms. Vessel tortuosity favors struts opening at the outside part of the curve. In these circumstances, entrapment of other materials, including stents, might occur. In our patient, the entrapment led to mechanical distortion of the previously implanted stent and dislodgement of the second stent. Entrapment of other interventional remnants such as wires, balloons or burrs are rare but relatively more frequent and may also result in stent mechanical disruption.¹
2) Extraction of a previously well-deployed stent. This is a very unusual complication that has been reported after cutting balloon entrapment.^2,3
3) Distortion of a previously implanted stent. Longitudinal traction force resulted in a severe elongation of the Taxus Liberté stent. The elongation of the stent was associated with stent shrinkage and loss of contact with the vessel wall. The distortion of the stent probably resulted from the massive, cascade-like link rupture facilitated by the decreased number of links that were linearly allocated and present in the new Taxus platform (Liberté) for improved flexibility (Figure 5). The diagnosis was suggested by fluoroscopy imaging, and confirmed by TEE and MSCT scans. To our knowledge, this is the first report of this kind of mechanical disruption.

4) Stent dislodgement. Stent dislodgement occurs in 0.1–0.3%^4–6 of all stent procedures and is associated with significant morbidity and mortality.⁷ Although it happened more frequently in the era of manually crimped stents, this complication still occurs with current premounted stents. Tortuosity, calcification, or both, are well-recognized causes of stent dislodgement. Preventive measures to avoid this complication include performing appropriate predilatation, not applying negative pressure to the stent delivery balloon until the lesion has been crossed, and not pushing too hard when a stent resists negotiating a curve. Once the complication has occurred, keeping the wire inside the stent is a priority in order to facilitate stent retrieval (with a small balloon, second wire or snare catheter) or in situ deployment.⁸ If the wire is lost and the stent is situated in the coronary artery, the stent may be crushed against the vessel wall by high pressure deployment of another stent. When the stent travels outside the coronary arteries (as occurs in half of the cases), it should be located and retrieved whenever possible.⁹ In our case, careful examination of the ascending aorta on fluoroscopy allowed us to identify the stent floating within the aorta. What we did not know at this point was how and to what structure the Driver stent was anchored. We decided to perform TEE, which revealed a moving long “wire” at the origin of the RCA. A MSCT scan confirmed that the “wire” was the RCA long Taxus stent that was enlarged to approximately 95 mm with the Driver stent attached to its tail. With this information, retrieval of the stents was easily accomplished through a 7 Fr introducer using a 25 mm Gooseneck Snare.
This case illustrates several interesting points: 1) distal stents should always be implanted before proximal ones, and recrossing with another stent over a recently deployed stent should be avoided; 2) contemporary thin-wall stents may be more likely to become distorted under specific mechanical conditions; and 3) new modalities of noninvasive imaging may provide important clues to understanding and treating complications that occur during percutaneous coronary interventions. Stents can be clearly imaged by MSCT and even, as in this case, with TEE.