Coronary Stent Pseudofracture

By Syed Maqbool, MD, DM, DNB
Longitudinal stent deformity is a phenomenon which has come into the limelight recently. Although reported cases describe a “concertina-like” stent strut overlap (compression), “pseudofracture” or gaps between struts due to longitudinal stretch have also been reported. This deformity has important clinical implications like stent thrombosis and in-stent restenosis. It can be prevented and needs awareness for recognition. The treatment may require an additional stent placement.

In this month’s Journal of Invasive Cardiology, we present a case of primary PCI to the left anterior descending that developed longitudinal stent deformity in the form of stretching/lengthening during positioning of the postdilatation balloon catheter.
Longitudinal integrity is only one desirable characteristic on which to base stent selection. Stent deliverability, strongly influenced by flexibility, is the property that cardiologists desire most, and designs that have high longitudinal integrity may not have high flexibility and deliverability. Cypher Select, which has a 6-connector design, had the greatest resistance to longitudinal distorting forces. This stent is no longer widely used because other designs have better flexibility, crossing profile, radio-opacity, side-branch access, and freedom from strut fracture. Besides connector number, the alignment of the connectors with the long axis of the stent may also be important for longitudinal integrity. Flexibility has been improved by designs with fewer connectors and thinner struts. Although reducing the number of connectors improves flexibility, the trade-off can be reduced longitudinal integrity. The analysis of 40 reports to the MAUDE registry provides insight into the nature and causes of longitudinal distortion, but not incidence because of under-recognition. Under-recognition is partly because cardiologists are not attuned to recognize distortions. Disruption may be difficult to recognize with the more radiolucent stents compared to the more radio-opaque stents, such as the Element platinum-chromium platform. Both stent shortening and elongation were reported. Deformation with separation or bunching of struts or both was most common in the proximal end of the stent, and less common at the distal end or in the middle of the stent. Shortening has been described as “concertina,” “accordion,” folded, squeezed together, pushed together, shrinkage, closing rings together, compression, wrinkling, and deformation. Elongation has been described as stretching, elongation, or separation. Causes of shortening include the post-dilating balloon, intravascular ultrasound catheter, guide catheter, another stent delivery system, thrombectomy catheter, and wire entanglement. Elongation or stretching occurs as a result of balloon catch during postdilatation balloon  catheter positioning because of wire bias. Shortening  was first noticed  with the Promus Element platform, where it was immediately apparent due to the enhanced radiographic visibility of the stent. However, this phenomenon has been seen to occur with all modern drug-eluting stent platforms from each of the major manufacturers. Elongation or stretching has been demonstrated in the Endeavor/Micro Driver platform clinically, as well as by bench testing, with a major adverse cardiovascular event rate of 36%.

In our patient, we deployed an Endeavor Resolute 2.75 x 28 mm stent, which contains the Microdriver platform. This platform has 7 crowns and, importantly, a single-helix backbone, which makes it more susceptible to longitudinal stretching. During positioning for postdilatation, the balloon got stuck in the middle of the stent, probably as a result of wire bias toward the malpositioned side. In the next cine frame, the stent seemed to have  lengthened, which got confirmed in stent viz. Optical coherence tomography was performed, which clearly showed that just before the distal end of the stent there was a considerable segment of the denuded artery and that the stent had lengthened. The mistake we made was that after feeling the catch, we tried to manipulate the same balloon which resulted in stretching the struts. The consequences of stretching could be dreadful. It is possible that if left with unrepaired stent deformation, probable poor apposition, and an unsupported segment of artery within the stent, then thrombosis would be a complication, especially if the unsupported section had dissection. This unsupported segment is obviously more susceptible to enhanced chances of in-stent restenosis.

 

Message: There is an inherent trade-off between flexibility and deliverability in contemporary stents; whenever a balloon catch is encountered, rather than forcing the balloon, one should change to a lower-profile compliant balloon and progressively increase the size.

A Selection of Articles on Stent Deformation:

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