Coronary balloon catheter tip damage. A bench study of a clinical problem.

OBJECTIVES: To confirm clinically that coronary balloon catheter tips may be damaged during bifurcation treatment with side-branch access through the side of a stent. On the bench, we aimed to assess the susceptibility of different balloon designs to damage. We compared catheter tip widths. We tested whether balloon tip flaring can cause stent distortion. BACKGROUND: We had observed that balloon catheters that failed to cross to a side-branch frequently exhibited tip damage. METHODS AND RESULTS: We examined microscopically for damage 82 balloon tips after clinical side-branch access. In a bench study, the forces required to compress catheter tips 0.5 mm were compared to assess susceptibility to damage. We compared tip widths of balloons of different nominal inflation diameters. We examined stents after side-branch access for distortion. In 42 of 48 (88%) of balloon tips from patients with resistance to or failure to cross through the side of a stent there was tip damage. Even when the balloon crossed without perceptible resistance, tip damage occurred in over half of balloons 18/34 (53%). Some balloon designs were more resistant to damage than others. Tips from balloons of different nominal diameters from the same manufacturer had the same width. Stent distortion caused by damaged balloon tips is improved by kissing balloon post-dilatation. CONCLUSIONS: Balloon tip damage is common with crossing between stent struts. This is one cause of failure of a balloon to access a side-branch and a new balloon should be used. If stent distortion is suspected, it should be corrected with kissing balloon post-dilatation.

An independent bench comparison of two bioresorbable drug-eluting coronary scaffolds (Absorb and DESolve) with a durable metallic drug-eluting stent (ML8/Xpedition).

AIMS: We compared the mechanical and physical properties and the safety from strut fracture of side branch and post-dilatation strategies for the Absorb and DESolve bioresorbable scaffolds with the durable metallic drug-eluting XIENCE Xpedition stent using largely independent bench testing. METHODS AND RESULTS: The strut thickness and crossing profile of the polymeric scaffolds was greater than those of the metallic drug-eluting stent. While all three devices recoiled after deployment, the DESolve enlarged between 10 mins and one hour returning to the immediate post-deployment diameter ("self-correction"). In 3.0 mm stents/scaffolds, the main branch post-dilatation safe threshold without fracture for Absorb was 3.8 mm at 20 atm, for DESolve was 5.0 mm at 20 atm whereas the ML8 did not fracture. For side branch dilatation with a 3.0 mm non-compliant balloon, the threshold before the Absorb fractured was 10 atm whereas the DESolve and ML8 did not fracture at 22 atm. The safe threshold for mini-kissing balloon post-dilatation in 3.0 mm scaffolds/stents with 3.0 mm non-compliant balloons was 5 atm for the Absorb whereas the DESolve and ML8 did not fracture up to 20 atm. CONCLUSIONS: The metallic stent has thinner struts, lower profile, and greater radial strength than the polymeric scaffolds. Different safe pressure thresholds exist for different scaffolds/stents. Unlike the others, the DESolve showed "self-correction" or enlargement after initial recoil.

Coronary stent durability and fracture: an independent bench comparison of six contemporary designs using a repetitive bend test.

AIMS: Stent fracture is important because it may cause adverse events. The interventional cardiologist needs independent data to aid stent selection. Stent designers need data to improve stent design. We used a repetitive bend test to compare durability and fracture for different stent designs. METHODS AND RESULTS: Tested were 15 examples of six designs (BioMatrix Flex, Vision, MULTI-LINK 8, Element, Promus PREMIER and Integrity). One end of a nominally deployed stent was mounted on a fixed mandrel. The other end was translated a distance of ±3.5 mm at a rate of 6 Hz until fracture or 10 million cycles completed. The numbers of cycles to fracture for the Vision design (288,411±193,391) and the MULTI-LINK 8 (314,475±239,869) were significantly greater than for the BioMatrix Flex design (38,904±13,160), p<0.001. The difference between Vision and MULTI-LINK 8 was not significant (p=0.79). The Element, PREMIER, and Integrity designs did not fracture. Most fractures were in the curved portions of connectors between hoops. CONCLUSIONS: The stent design which fractured most readily was the BioMatrix Flex. The most flexible designs did not fracture and, in general, stents with three connectors were more likely to fracture than those with two connectors between loops.

Absorb everolimus-eluting bioresorbable scaffolds in coronary bifurcations: a bench study of deployment, side branch dilatation and post-dilatation strategies.

AIMS: To provide bench insights which may predict safety and efficacy of side branch dilatation (SB) and kissing balloon post-dilatation (KBPD) in Absorb everolimus-eluting bioresorbable scaffolds deployed in bifurcations. METHODS AND RESULTS: Stages of deployment and post-dilatation of scaffolds (3.0 and 3.5 mm diameter) in bifurcation phantoms were imaged by fluoroscopy, light microscopy and micro-computed tomography. Dilatation through the scaffold side displaced struts from the side branch (SB) lumen, but caused main branch (MB) malapposition opposite the SB, MB scaffold narrowing beyond the SB, and protrusion of struts into the SB. Scaffold distortion was corrected by MB post-dilatation or by mini-kissing balloon post-dilatation (mini-KBPD). When 3.0 mm diameter balloons were used for SB dilatation or mini-KBPD in 3.0 mm Absorbs, strut fracture did not occur at or below inflation pressures of 10 and 5 atm, respectively. Above these thresholds, the likelihood of strut fracture increased with increasing pressure. Fractures were usually single without malapposition, but mini-KBPD or post-dilatation with high inflation pressures sometimes caused multiple strut fractures and lumen compromise. CONCLUSIONS: SB dilatation of an Absorb caused MB distortion which was corrected by MB post-dilation or low-pressure mini-KBPD without scaffold damage below pressure thresholds. These benchtop insights may help guide the clinical deployment of Absorb scaffolds in bifurcations and might enhance clinical outcomes but need clinical confirmation.

Stent longitudinal strength assessed using point compression: insights from a second-generation, clinically related bench test.

BACKGROUND: Stent longitudinal distortion, while infrequent, can lead to adverse clinical events. Our first bench comparison of susceptibility of different stent designs to distortion applied force to the entire circumference of the proximal stent hoop. The test increased understanding of stent design and led to recommendations for design change in some. Our second-generation test more closely mimics clinical scenarios by applying force to a point on the proximal hoop of a malapposed stent. METHODS AND RESULTS: Each 3-mm-diameter stent was secured in a test apparatus so that its proximal 5 mm was malapposed in a 3.5-mm tube. An instron applied force to the proximal hoop of each of 5 examples of each of 6 stent designs using a narrow rod so that force applied and distance compressed could be measured. Hoops on the side of the force were pushed together, became malapposed, and obstructed the lumen. In addition, the proximal stent hoop tilted causing malapposition, the contralateral side of the stent from the applied force causing lumen obstruction. CONCLUSIONS: This second-generation, more clinically relevant test showed the Biomatrix Flex was the most resistant to deformation and the Element the most easily deformed. The addition of more connectors between the proximal hoops in the Promus Premier design has reduced the potential for distortion when compared with the Element, so that distortion was similar to the Vision, Multi-Link 8, and Integrity designs. The test also provided insight into the way in which stents are likely to distort in clinical practice.