Longitudinal Stent Deformation

Satyam Rajvanshi

• More contemporary stent benefits– increased deliverability and conformability– Improved PCI outcomes

Improved stent deliverability achieved through– Novel alloys (cobalt chrome or platinum chrome)– Thinner struts– Newer 3D designs– in some stents—reduced number of connectors

between adjacent stent rings (crowns) – improves SB access also

• Even with reduction in strut thickness, innovative designs have enabled maintenance of radial strength

• However, longitudinal (or axial) strength may be lower with these new designs and is not routinely reported by stent manufacturers

• Longitudinal stent deformation (LSD) is defined as the accidental mechanical distortion or shortening of a stent in the longitudinal axis following stent deployment

THE ANGIOGRAPHIC “WEDDING BAND”!

EuroIntervention 2012;8:267-274

EuroIntervention 2011

LSD

• 0.2% incidence – 0.2% of 4455 PCIs• 0.09% stents deployed

• 12 published cases : 11 proximal crunch and 1 distal crunch– 7 Promus Element (Pt-Cr)– 2 Biomatrix (SS)– 1 Endeavour (Co-Cr)– 1 Taxus liberte (SS)– 1 Resolute Integrity (Co-Cr)

• Average length of stents implanted – 30.7 mm

• Most common cause– Unexpected or Excessive penetration of • Guide catheter• Guide catheter extension• Proximal EPD in SVG-PCI

– Mechanical conflict between proximal malapposed stent struts and Post-dialatation balloon

EuroIntervention 2012

• Stents inflated to nominal pressure in a test fixture

• Stent length 28-30 mm• Longitudinally compressed by 14 mm• Longitudinal compression force - measured as a

function of the compression distance • Plot of the longitudinal compression force versus

amount of longitudinal compression was generated

Clinically relevant force – 50 gms

Clinically relevant force – 50 gms

Column Strength:Key to lessLSD

• Recommendation– Additional stent connectors be added to the

Element stent design

– Addressed in Promus Premier

• Major LIMITATION!– All 6 authors – Abott vascular employees– Clear conflict of interest!

• Also, clinicians said LSD is as common is all platforms – but more recognised in ELEMENT – the flipside of better visibility!

Circ Cardiovasc Interv February 2014

Point compression on proximal malapposed segment

Partial recoilBut permanent deformability

Biomatrix Flex - most resistant to deformation Element - most easily deformed

SITUATIONAL EXAMPLES

• Withdrawal of a stent delivery system when the balloon gets caught in struts of the deployed stent

• Crossing of a newly deployed stent with a stent delivery system for treatment of a distal lesion

• Crossing of a balloon dilatation catheter through a deployed stent for post-dilation of the stent

• Guide catheter contact with the stent after stent deployment due to ostial location or deep-seating of the guide

• IVUS pull-back during post-deployment inspection of the deployed stent

Malapposition of struts – MC underlying pathophysiology

ANGIOGRAPHIC OUTCOME AFFECTED? YES

BUT DOES IT AFFECT MACE?

AVOIDANCE AND TREATMENT

CONCLUSIONS

• Longitudinal stent deformation can occur secondary to a variety of mechanisms

• Rare but also under-recognised and under-reported

• More common in complex angiographic disease• Identification is important as, left untreated, it

may be associated with MACE• Although seen with several different stents, in

the published series - more commonly observed with the Promus Element stent. Engineering studies also give scientific logic behind this.

Before PCI

After PCI