Bench test and in vivo evaluation of longitudinal stent deformation during proximal optimisation

Abstract

Background: While radial stent deformation has been thoroughly investigated, data on longitudinal deformation are scarce.

Aims: The aim of the study was to describe longitudinal stent deformation associated with the proximal optimisation technique (POT).

Methods: Longitudinal stent deformation was assessed by bench testing and by clinical evaluation. Bench testing was performed in silicone models using 3.00 (n=15) and 3.50 mm (n=14) stent platforms. After deployment, stents were sequentially post-dilated in the proximal main branch up to 5.50 mm, in increments of 0.50 mm, in order to simulate a spectrum of overexpansion. Stent length was redefined by optical coherence tomography (OCT) after each step. Clinical data were collected retrospectively from OCT-guided bifurcation percutaneous coronary intervention cases.

Results: In bench tests, POT has led to significant stent elongation in all cases. The magnitude of elongation was comparable between the 3.00 and the 3.50 mm stent platforms, with 0.86±0.74 mm vs 0.86±0.73 mm, respectively (p=0.71), per 0.5 mm overexpansion. For 3.00 mm stent platforms, maximal elongation was 4.31±1.47 mm after up to 5.5 mm overexpansion. For 3.50 mm platforms, maximal elongation was 2.87±0.94 mm after up to 5.5 mm overexpansion. Thirty-six clinical cases were analysed, of which 22 (61%) were performed in the distal left main. Post-dilation was performed with 0.98±0.36 mm absolute overexpansion, resulting in 2.22±1.35 mm elongation, as compared to nominal stent length.

Conclusions: Overexpansion by POT results in proximal stent elongation. This has to be considered once the stent length is selected and the stent is positioned, especially in the left main stem, where proximal overexpansion is marked and accurate ostial landing is critical.

Central illustration. Observed longitudinal stent deformation in clinical cases per case (left) and overall (right).

Dotted red line indicates reference.

Figure 1. Longitudinal stent behaviour during proximal optimisation in 3.00 mm stent platforms (A) and in 3.50 mm stent platforms (B) in bench.

Figure 2. Bench observation of lengthening in 3.00 mm stent platforms (left column) and in 3.50 mm stent platforms (right column).

Ruler scale is per two millimetres. White arrow indicates the stretching of the strut construction at the level of the distal branch ostium.

Figure 3. Comparison of absolute lengthening.

A) Overall in 3.00 mm (blue) and 3.50 mm (red) stent platforms and per steps of overdilation (B) for 3.00 mm and (C) for 3.50 mm platforms.

Figure 4. Case example.

Lengthening of the proximal portion of a 3.0 mm stent after 4.5 mm proximal optimisation as shown by optical coherence tomography. POT: proximal optimisation technique

Figure 5. The "melon seed effect" and design of the POT balloon.

Mechanism of the “melon seed effect” of the POT balloon (A1-A3) and demonstration of the conical tip of a balloon catheter as compared to balloon marker (white arrow) (B). Red arrows indicate the proximal migration of the distal balloon edge. Grey arrows indicate the resulting separation of the stent struts at the level of the junction between pMB and dMB (corresponding to the carina in vivo). dMB: distal main branch; pMB: proximal main branch; POT: proximal optimisation technique