Finite element analysis of cutting balloon expansion in a calcified artery model of circular angle 180°: Effects of balloon-to-diameter ratio and number of blades facing calcification on potential calcification fracturing and perforation reduction

Abstract

Calcified artery lesions cause stent under-expansion and increase the risk of in-stent restenosis and stent thrombosis. Cutting balloons facilitate the fracturing of calcification prior to stent implantation, although vessel dissection and perforation are potential issues. In clinical practice, calcifications having maximum calcium angles ≤ 180° are rarely fractured during conventional balloon angioplasty. We hypothesize that the lesion/device diameter ratio and the number of blades facing a non-circular calcified lesion may be crucial for fracturing the calcification while avoiding vessel injury. The geometries of the cutting balloons were constructed and their finite-element models were generated by folding and wrapping the balloon model. Numerical simulations were performed for balloons with five different diameters and two types of blade directions in a 180° calcification model. The calcification expansion ability was distinctly higher when two blades faced the calcification than when one blade did. Moreover, when two blades faced the calcification model, larger maximum principal stresses were generated in the calcification even when using undersized balloons with diameters reduced by 0.25 or 0.5 mm from the reference diameter, when compared with the case where one blade faced the calcified model and a balloon of diameter equal to the reference diameter was used. When two blades faced the calcification, smaller stresses were generated in the artery adjacent to the calcification; further, the maximum stress generated in the artery model adjacent to the calcification under the rated pressure of 12 atm when employing undersized balloons was smaller than that when only one blade faced the calcification and when lesion-identical balloon diameters were used under a nominal pressure of 6 atm. Our study suggested that undersized balloons of diameters 0.25 or 0.5 mm less than the reference diameter might be effective in not only expanding the calcified lesion but also reducing the risk of dissection.

Fig 1

Geometries and mesh models for (a) blade, (b) balloon with pad and blade, and (c) coronary artery with calcified artery model.

Fig 2. Expansion of cutting balloon in the stenotic calcified artery models.

(a) Crimp and compression process of a folded balloon. (b) Configuration of cutting balloon in the calcified artery model. (c) Two types of models for the analysis (Type 1: one blade is placed inside the calcification model, Type 2: two blades are placed inside the calcification model).

Fig 3. Stress distributions in the calcified artery models for Type 1 and Type 2 at rated pressure (12 atm) with five different balloon diameters.

The cross-sectional stress distributions in the thickness-wise direction were at the longitudinal end of the calcification models. The location of label “A-A” is the longitudinal end of the calcification. The label “LW” denotes the lumen width of calcification at the longitudinal end at balloon inflation.

Fig 4. Peak values of the maximum principal tensile stresses in the calcification models along the longitudinal direction when the cutting balloon is inflated at the rated pressure (12 atm).

Fig 5. Stress distributions in the artery model for Type 1 and Type 2 at the rated pressure (12 atm) for five different balloon diameters.

Fig 6. Effects of cutting balloon diameter and blade direction on the maximum principal tensile stresses in the models of the calcification and artery adjacent to the calcification.

(a) Maximum principal tensile stresses in the calcification model for Type 1 and Type 2 for five different balloon diameters. (b) Maximum principal tensile stresses in the artery model adjacent to the calcification for Type 1 and Type 2 for five different balloon diameters.

Fig 7. Incidence of slippage during the inflation of balloons of diameters 2 and 2.25 mm.

Fig 8. Changes in the angles of the blades during inflation.

(a) Change in the angle of the blade facing the calcification model during expansion. (b) Comparison of angle changes among 2, 2.25, 2.5, 2.75, and 3 mm cutting balloons for the entire pressure range.