Measuring arterial strain induced by endovascular stents

Acute Stent-Induced Endothelial Denudation: Biomechanical Predictors of Vascular Injury

Recent concern for local drug delivery and withdrawal of the first Food and Drug Administration-approved bioresorbable scaffold emphasizes the need to optimize the relationships between stent design and drug release with imposed arterial injury and observed pharmacodynamics. In this study, we examine the hypothesis that vascular injury is predictable from stent design and that the expanding force of stent deployment results in increased circumferential stress in the arterial tissue, which may explain acute injury poststent deployment. Using both numerical simulations and ex vivo experiments on three different stent designs (slotted tube, corrugated ring, and delta wing), arterial injury due to device deployment was examined. Furthermore, using numerical simulations, the consequence of changing stent strut radial thickness on arterial wall shear stress and arterial circumferential stress distributions was examined. Regions with predicted arterial circumferential stress exceeding a threshold of 49.5 kPa compared favorably with observed ex vivo endothelial denudation for the three considered stent designs. In addition, increasing strut thickness was predicted to result in more areas of denudation and larger areas exposed to low wall shear stress. We conclude that the acute arterial injury, observed immediately following stent expansion, is caused by high circumferential hoop stresses in the interstrut region, and denuded area profiles are dependent on unit cell geometric features. Such findings when coupled with where drugs move might explain the drug–device interactions.

Experimental mechanical strain measurement of tissues

Strain, an important biomechanical factor, occurs at different scales from molecules and cells to tissues and organs in physiological conditions. Under mechanical strain, the strength of tissues and their micro- and nanocomponents, the structure, proliferation, differentiation and apoptosis of cells and even the cytokines expressed by cells probably shift. Thus, the measurement of mechanical strain (i.e., relative displacement or deformation) is critical to understand functional changes in tissues, and to elucidate basic relationships between mechanical loading and tissue response. In the last decades, a great number of methods have been developed and applied to measure the deformations and mechanical strains in tissues comprising bone, tendon, ligament, muscle and brain as well as blood vessels. In this article, we have reviewed the mechanical strain measurement from six aspects: electro-based, light-based, ultrasound-based, magnetic resonance-based and computed tomography-based techniques, and the texture correlation-based image processing method. The review may help solving the problems of experimental and mechanical strain measurement of tissues under different measurement environments.

FSI SIMULATION OF A HEALTHY CORONARY BIFURCATION FOR STUDYING THE MECHANICAL STIMULI OF ENDOTHELIAL CELLS UNDER DIFFERENT PHYSIOLOGICAL CONDITIONS

Atherosclerosis is a world-spread and well-known disease. This disease strongly relates to the endothelial cells (ECs) function. Normally, the endothelial cells align in the flow direction in the atheroprotected sites; however, in the case of atheroprone sites these cells orient randomly. The mechanical stimuli such as wall shear stress and strains could determine the morphology and function of the endothelial cells. In the present study, we numerically simulated the left main coronary artery (LCA) and its branches to left anterior descending (LAD) and left circumflex coronary (LCX) artery using fluid–structure interaction (FSI) modeling. The results were presented as longitudinal and circumferential strains of ECs as well as wall shear stress. Wide ranges of heart rate, cardiac motion, systolic and diastolic pressures were considered and their effects on mechanical stimuli were described in detail. The results showed that these factors could greatly influence the risk of atherosclerosis and the location of atherosclerotic lesions.

A morphological–mechanical explanation of edge restenosis in lesions treated with vascular brachytherapy

PURPOSE

Edge restenosis in stenotic lesions treated by implantation of a conventional stent followed (or preceded) by a catheter-based brachytherapy is often attributed to "geographic miss" (GM). We propose a complementary (or, possibly, alternative) explanation based on the concept that a clear postprocedural mismatch between the in-stent lumen and the normal (undilated) lumens of the proximal and/or distal vessel segments results in an excessive, damageable increase of axial wall stress in these segments.

METHODS

The possible poststenting situations at both margins of a stent are examined, and based on the presence or absence of an increase in axial wall stress, predictions are made about the lesion evolution. The concept is then also examined in the light of published observations.

RESULTS

None of the analyzed observations appeared to be incompatible with the proposed morphological-mechanical explanation.

CONCLUSION

From a mechanical point of view, optimal matching of the proximal and distal stent diameters to the corresponding normal diameters of the adjacent arterial segment is likely to reduce the rate of edge restenosis.

Restenosis rates with flexible GFX stents (REFLEX): clinical and angiographic results

The objective of this prospective, multicenter, observational trial was to evaluate the procedural results and longterm outcomes of the flexible AVE GFX coronary stent in native coronary lesions. The trial included 137 consecutive patients (111 [81%] men, age 63.1 +/- 9.2 years) with one vessel disease (n = 76 [55.5%]), two vessel disease (n = 31 [22.6%]), and three vessel disease (n = 30 [21.9%]) with ischemia secondary to a significant denovo lesion (diameter > or = 3 mm, length < or = 18 mm) in a native coronary artery. Stent deployment was successful in 97.8% (134/137) of patients. Angiographic follow-up at 6.1 +/- 1.2 months was available in 111 (82.8%) of 134 patients. All angiographic images were analyzed by an independent core lab. The primary end point was the binary restenosis rate. In-hospital major cardiac events occurred in 3.7%. No postdischarge major adverse cardiac events occurred, except for one abrupt closure (0.7%). Angiographic restenosis was documented in 22 (19.8%) of 111 patients. The GFX stent is easy to handle with high success and low restenosis rates in patients with simple lesions in native coronary arteries and, thus, compares favorably with other sophisticated stents.

Simultaneous Measurements of Arterial Diameter and Blood Pressure to Determine the Arterial Compliance, Wall Mechanics and Stresses In vivo

BACKGROUND

to develop a periarterial dimensional clip-probe which, associated with endovascular pressure measurement, real-time digital signal processing/data treatment systems, enables characterisation of the basic wall mechanics in given arterial sites.

DESIGN

experimental study.

MATERIAL

a facing pair of ultrasonic crystals was incorporated in periarterial highlight probes, made of sterilisable silicone and manufactured from computer-designed stainless steel casts. The A/D converted diameter and pressure (from an endovascular micro-tip probe) signals, triggered by the ECG, were on-line processed to provide their respective profiles during an averaged cardiac cycle, and subsequently the arterial wall physics. The technique was tested in the iliac and renal arteries in eight pigs.

RESULTS

the technique was found to indicate adequately that arterial responses to distending blood pressure, as given by Petersons modulus and relative pulsatility, were identical in renals and iliacs. In contrast, the compliance, circumferential incremental elastic modulus and midwall circumferential stress were higher in iliacs than in renals, whereas arterial stiffness of the renals surpassed that of the iliacs.

DISCUSSION

the technique with sterilisable probes produces in vivo pressure-diameter relationships, arterial compliance, and wall mechanics and stresses, whatever the arterial size. The porcine iliacs and renals are elastic and viscorigid arteries, respectively.