The diameter of the ostial and proximal left main coronary artery is usually larger than 5.0 mm. However, there are no > 4.0-mm-diameter coronary DESs available in China and some other countries till now. Our test results show that none of the six types of 4.0-mm-diameter DESs were fractured after high-pressure dilatation with a 5.0-mm noncompliant balloon and that LSD was caused by post-dilatation after stent implantation. While the Nano Plus stent was apposed incompletely after post-dilatation, the other stents were dilatated to a diameter of 5.0 mm and were well apposed.
Two previous studies showed that 4.0-mm-diameter stents could be dilatated to a diameter of 5 mm or higher [
2,
3]. However, these studies did not include tests using an in vitro blood vessel model and therefore could not simulate the actual blood vessels. Additionally, the observations and measurements were obtained by three-dimensional reconstructions using optical microscopy and Micro-CT imaging. In contrast, we used a truncated cone-shaped silicone tube to model the left main coronary artery, which is closer to the actual condition of the blood vessel. Furthermore, we observed the lumen by OCT, which is more comparable to the in vivo situation, and the measurements of the changes in the longitudinal axis and the apposition rates of the stents are more accurate and intuitive. Regarding left main coronary lesions, a certain risk exists when assessing the severity of stenosis only through angiography. Current myocardial revascularization guidelines recommend interventional therapy under the guidance of intravascular imaging for left main lesions, which is conducive to optimization of stent implantation to ensure sufficient apposition of the stent [
6]. A previous in vitro OCT study suggested that stent malapposition is the main cause of stent thrombosis [
7]. Therefore, good stent apposition is extremely important in the treatment of ostial left main coronary lesions. Our result revealed that stent malapposition might be positively correlated with the percentage change in stent length (the LSD rate). LSD, which is defined as distortion of a stent in the longitudinal axis, has been recognized as an important complication during PCI procedures [
8]. Various risk factors have been identified for LSD, such as lesion complexity, stent design, post-dilatation, and supporting devices. Apart from the factors related to lesion characteristics and the complexity of the procedures, stent material and design play vital roles in stent longitudinal integrity. The connectors which join the adjacent stent rings provide longitudinal support for the stent. The fewer connectors attached to stent rings, the larger open cells the stents have. Compared with stents with more than two connectors, less force was required to compress or elongate stents with two connectors [
9]. LSD may be difficult to detect angiographically, and the use of OCT or intravascular ultrasound (IVUS) can help confirm the diagnosis and guide treatment decisions, as well as avoid complications such as stent thrombosis [
10]. In our current study, we showed that the LSD rates of the Firehawk and Nano Plus stents were greater than the other stents by OCT examination. The higher LSD in these two stents could be due to relatively few connectors compared with other stent platforms. Previous studies suggested that the proximal optimization technique (POT) and post-dilatation from the proximal site of the stent were useful for reducing the incidence of LSD [
8,
11].
Stent malapposition can result in short- or long-term adverse clinical events. The material and design of the stent and post-dilatation strategies affect acute recoil and stent expansion. 316 L stainless steel, open-cell design and stent with thin struts are likely to cause low radial strength, subsequently leading to stent malapposition. Moreover, the number of the connectors between loops and the orientation of these connectors also contribute to radial support. Post-dilatation using large non-compliant balloon is usually performed to overcome the malapposition. This is extremely important for complex coronary lesions, such as left main lesions, severe calcification and bifurcation lesions. A strategy of several short post-dilatations with non-compliant balloon was better than a single long inflation for improving the recoil and enlarging the stent area. However, no single stent design is suitable for all variety of CAD and improvement in one aspect of a stent will compromise another aspect. Understanding this tradeoff and the mechanical properties of each stent design may help interventional cardiologists in individualized device selection and facilitate procedural success.