Breaking the limit: mechanical characterization of overexpanded balloon expandable stents used in congenital heart disease.

Objective: Intravascular stent placement in patients with congenital heart disease has replaced several surgical procedures because the desired outcome is achieved with a lower risk of complications. However, the blood vessels of children undergo a two- to threefold diameter increase due to somatic growth creating a dilemma: Can stents implanted in infants and children be serially dilated to significantly larger diameters without losing integrity and important mechanical characteristics? Our aim was to assess the expansion potential and to characterize mechanical parameters of balloon expandable stents at the maximum expansion diameter.

Design: Sixteen commonly used stent designs were evaluated. Physical attributes (sheath size and guide wire size) and the following mechanical parameters were determined, compared, and contrasted: fracture diameter, maximum expansion diameter, stent integrity, outer diameter, diameter uniformity, diameter recoil, length change, radial stiffness, and radial strength.

Results: Stents were dilated to an average of 1.7 times (range from 1.3 to 2.4 times) the nominal expansion diameter without losing mechanical integrity. Stents at the maximum expansion diameter maintained diameter uniformity (with less than 3.2% difference) and demonstrated minimal diameter recoil once the balloon catheter was deflated (less than 3.6% recoil). At the maximum expansion diameter, stent length varied depending on stent type. When dilated to the maximum expansion diameter, radial stiffness and radial strength of all stents increased compared with the stents' nominal expansion diameter.

Conclusions: Balloon expandable stents maintain excellent mechanical characteristics when dilated beyond their manufacturers' recommended nominal expansion diameter. These results support the use of balloon expandable stents in smaller vessels that require future serial redilation.