Longitudinal Deformation of a Stent with the POT Technique

The fractal geometry of coronary bifurcations offers a mismatch between the proximal diameter of the main branch and the distal branches that make up the bifurcation. Angioplasty in this area can be performed through different techniques depending on plaque distribution, and the particular geometry of each bifurcation.

Deformación longitudinal de un stent con la técnica de POT

Overall, and regardless of the strategy used, there is a common step: the proximal optimization technique (POT). Since the stent diameter chosen must follow distal vessel caliber (to prevent vascular trauma), the proximal segment may often be under-expanded. If the mismatch is significant, successive POTs may result in stent overexpansion, leading to structural deformation. There is not much literature on this “longitudinal behavior.”

The aim of this paper was to analyze and describe the longitudinal patterns of stent deformation during POT overexpansion, both on a test bench and in the clinical analysis of a retrospective registry.

In evaluating the behavior on the test bench (siliconized tube), the POT was simulated in two different models with a common proximal main segment (internal diameter >6.0 mm) and a 1-mm long transition connecting to the distal segment (3.0-mm or 3.5-mm platforms).

Testing was performed with 5 different stent types: Orsiro, Resolute Onyx, Sinergy, Sinergy Megatron, Ultimaster, and Xience (all of them 28-mm long), with an evaluation of different lengths over the proximal area. Optical coherence tomography (OCT) was performed systematically twice after stent implantation, and with every repeat POT.

For clinical control, researchers analyzed the OCT database of bifurcation lesion angioplasties from four participating centers over 2 years.

In bench testing, 15 tests were performed with the 3.0-mm platform, and 14 tests with the 3.5-mm platform. When testing the 3.0 mm platform, significant elongation was observed with each 0.5-mm increase in POT, with a maximum elongation of 4.31 ± 1.47 mm when reaching an overexpansion of 5.5 mm.

The same effect was evidenced in the 3.5-mm platform with a significant elongation every 0.5 mm, with a maximum elongation of 2.87 ± 0.94 mm at the proximal level (meaning a relative elongation of 19.45%).

A significant difference was observed when comparing mean elongation in different proximal lengths (10 mm: 1.34 ± 1.36 mm; 15 mm: 1.64 ± 1.30 mm; 20 mm: 2.12 ± 1.89 mm; p = 0.05). When analyzing the different stent types, no significant differences were observed, with no stent fractures in the OCT analysis.

Clinical analysis included 36 cases (most in the distal main coronary artery). In this sense, OCT imaging showed a mean elongation of 2.22 ± 1.35 mm (p < 0.01).

Conclusions

When analyzing a test bank and bifurcation cases from an OCT registry, a relevant elongation at the proximal level was evidenced in the simulated model with each 0.5 mm overexpansion. These data were confirmed in the retrospective analysis of the OCT registry of bifurcation lesions, which showed an elongation greater than 2 mm in the proximal segment. These results should be taken into account when deciding on the stent, mainly in segments such as the left main coronary artery, since poor apposition could result in vessel revascularization failure with the subsequent clinical consequences that this entails.