Impact of post-dilatation on longitudinal stent elongation: An in vitro study

Impact of lesion morphology on stent elongation during bifurcation PCI: an in vivo OCT study

BACKGROUND

Recent observations in silico and in vivo reported that, during proximal optimisation technique, drug-eluting stents (DES) elongate, challenging conventional wisdom. The interaction between plaque morphology and radial expansion is well established, but little is known about the impact of plaque morphology on elongation.

AIMS

We aimed to assess the longitudinal mechanical behaviour of contemporary DES in vivo and evaluate the relationship between post-percutaneous coronary intervention (PCI) stent elongation and lesion morphology, as assessed with optical coherence tomography (OCT).

METHODS

Patients treated with OCT-guided PCI to left main or left anterior descending artery bifurcations, between July 2017 and March 2022, from the King's Optical coherence Database Analysis Compendium were included. Patients were excluded if there were overlapping stents, if they had undergone prior PCI, or if there was inadequate image quality. Lesions were characterised as fibrocalcific, fibrous or lipid-rich by pre-PCI OCT. Following stent post-dilatation, stent expansion and final stent length were assessed. The primary outcome was the percentage change in stent length from baseline.

RESULTS

Of 501 eligible consecutive patients from this period, 116 were included. The median age was 66 years (interquartile range [IQR] 57-76), 31% were female, and 53.4% were treated for an acute coronary syndrome. A total of 50.0% of lesions were classified as fibrocalcific, 6.9% were fibrous, and 43.1% were lipid-rich. The change in relative stent length was 4.4% (IQR 1.0-8.9), with an increase of 3.1% (IQR 0.5-6.3) in fibrocalcific lesions, 3.3% (IQR 0.5-5.9) in fibrous lesions, and 6.4% (IQR 3.1-11.1) in lipid-rich plaque (p=0.006). In multivariate regression modelling, lipid-rich plaque was an independent predictor of stent elongation (odds ratio 3.689, 95% confidence interval: 1.604-8.484).

CONCLUSIONS

Contemporary DES elongate following implantation and post-dilatation, and this is significantly mediated by plaque morphology. This is an important consideration when planning a strategy for DES implantation.

Evaluation of post-dilatation on longitudinal stent deformation and postprocedural stent malapposition in the left main artery by optical coherence tomography (OCT): an in vitro study

BACKGROUND

The diameter of the ostial and proximal left main coronary artery can be greater than 5.0 mm. However, the diameters of the mostly available coronary drug-eluting stents (DESs) are ≤ 4.0 mm. Whether high-pressure dilatation can increase the diameter of stents from 4.0 to 5.0 mm and whether post-dilatation leads to longitudinal stent deformation (LSD) of 4.0-mm-diameter stents have rarely been studied. Therefore, this study aims to evaluate LSD and stent malapposition of six types of commercially available 4.0-mm-diameter stents in China in a 5.0-mm-diameter artificial blood vessel model by optical coherence tomography (OCT) in vitro.

METHODS

The left main coronary artery was simulated by a truncated cone-shaped silicone tube. The internal diameters were 4.0 mm at one end of the silicone tube and 5.0 mm at the other end. Six different types of coronary stents widely used in China were selected for this study. Each stent was respectively implanted into the simulated blood vessel and dilated to a diameter of 4.2 mm according to the stent-balloon pressure compliance table. The stents were subjected to post-dilatation with a 5.0 × 15-mm noncompliant balloon. The LSD ratio of the longitudinal axis of each stent and stent malapposition were measured through OCT, and any fractures of the stents were determined.

RESULTS

None of the six types of stents fractured following post-dilatation. The longitudinal axes of the BuMA and Excrossal stents were slightly shortened, while the other stents were elongated after high-pressure post-dilatation. All stents expanded to a diameter of 5.0 mm without incomplete stent apposition, except for the Nano Plus stent, which remained malapposed after high-pressure post-dilatation.

CONCLUSION

All 4.0-mm-diameter stents can be expanded to a diameter of 5.0 mm by noncompliant balloon post-dilatation without stent strut fracture. Most stents were found to be well apposed after high-pressure post-dilatation. However, LSD was observed after post-balloon dilatation. Stent malapposition might be positively correlated with the percentage change in stent length.

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

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.

Longitudinal stent elongation or shortening after deployment in the coronary arteries: which is dominant?

Background

Stent manufacturers always record stent shortening data while they do not record stent elongation data. The aim of this study is to identify both stent shortening and elongation occurring after deployment in the coronary arteries and know their percentage.

Results

The length of coronary stents was measured by intravascular ultrasound (IVUS) by (1) edge-to-edge (E-E) length, measured from the appearance of the first distal strut to the last proximal strut, and (2) area-to-area (A-A) length, measured from the first distal struts seen at more than one IVUS quadrant to the last proximal struts seen at more than one IVUS quadrant. Stent shortening was defined as both E-E and A-A lengths were shorter than the manufacturer box-stated length (shortened group). Stent elongation was defined as both E-E and A-A lengths were longer than the manufacturer box-stated length (elongated group), otherwise unchanged group. Consecutive 102 stents deployed in ischemic patients were included. Stent elongation was detected in 67.6% (69 stents), and shortening was detected in 15.7% (16 stents), while unchanged stents were detected in 16.7% (17 stents). Although the 3 groups had similar box-stated length and predicted foreshortened length, they had significantly different measurements by IVUS, p<0.001 for each comparison. Differences from box-stated length were 1.9±1.4mm, −1.4±0.4mm, and 0.4±0.3mm, respectively, p<0.001. The elongated group had significantly longer differences from the corresponding box-stated and predicted foreshortened lengths, while the shortened group had significantly shorter differences from the corresponding box-stated length and similar foreshortened length. By multinomial regression analysis, the plaque-media area and stent deployment pressure were the independent predictors of the stent length groups, p=0.015 and p=0.026, respectively.

Conclusions

Change in stent length is not only shortening—as mentioned in the manufacturer documents—but also stent elongation. Stent elongation is dominant, and the most important predictors of longitudinal stent changes are plaque-media area and stent deployment pressure.