Geometrical and stress analysis of factors associated with stent fracture after melody percutaneous pulmonary valve implantation.

BACKGROUND Patients treated with the Melody device (Medtronic) for percutaneous pulmonary valve implantation experience stent fractures in ≈25% of the cases. The aim of this study is to identify the risk factors associated with fracture using 3-dimensional (3D) analyses. METHODS AND RESULTS In situ 3D shape of the Melody stent was reconstructed from 42 patients using procedural biplane fluoroscopy images, after balloon inflation, at systole and diastole. Four geometric parameters at systole and their variation during balloon deflation and cardiac cycles were measured to describe the 3D strut, cell, section, and stent configuration. Furthermore, patient-specific computer simulations were set up to replicate the history of stent deformations for each patient. Maximum and minimum principal stresses resulting from these analyses were monitored during balloon deflation and cardiac cycle. Univariate logistic regression analyses of 21 geometric parameters and of 4 stress parameters respectively, identified the decreased stent circularity after balloon deflation (odds ratio 0.98; 95% confidence interval, 0.96-0.99; P=0.006) and large compressive stresses during balloon deflation (odds ratio, 0.98; 0.96-0.997; P=0.03), as associated with the risk of fracture. In a multivariable logistic regression model, the 2 covariates identified on univariate analysis (1 geometric and 1 stress) were found to be independently associated with the risk of fracture. The resultant statistical model correctly identified fracture/no fracture in 93% of patients. CONCLUSIONS Changes in stent section shape after balloon deflation are important variables influencing fracture. This methodology could help design tailored follow-up for patients after percutaneous pulmonary valve implantation.