CLINICAL EVALUATION - retrospective appraisal of device performance with critical examination of any premature device failures.

Services include:

·         Failure analysis

o        Fractography

o        Optical microscopy

o        Metallography

o        Scanning Electron Microscopy (SEM)

·         Patient imaging analysis - DICOM, Fluoro, MRI, CTA

·         FDA Manufacturer and User Facility Device Experience Literature Survey

In Vivo failure of an artificial, pyrolytic carbon mitral heart valve:

Optical and scanning electron microscopy confirmed the presence of adherent biological debris (most likely thrombus) trapped in the hinge, thereby providing locally elevated stress-concentrations due to an effective interference fit or artificial tolerance mismatch when the leaflet actuated across the hinge recess.  This stress-concentration in the edge of the leaflet resulted in fatigue crack nucleation (see micrograph below with the origin in the lower right corner), propagation, complete fracture, and eventual leaflet fragment escape and migration into the left ventricle.

Prototype pulmonary artery Nitinol stent fracture during animal trials:

Explantation of prototype pulmonary artery stents following a 180 day animal trial revealed several fractures near a weld joint.  Scanning electron microscopy (SEM) of the fracture surfaces revealed that the weld was unaffected by the cyclic loads during breathing; however smooth tooling gouges (right side of wire in micrograph below) in the Nitinol wire surfaces ~1 cm from the weld resulted in locally elevated stresses and promoted fatigue crack nucleation (origin shown in top right of micrograph below).

Patient Image Analysis:

Cine fluoroscopy of a patient presenting with right flank pain following a renal artery stent placement procedure ~1 year earlier revealed an in vivo stent fracture due to native ostial rigid calcification and distally-angled artery branching from the aorta. <link to paper>

FDA MAUDE Database Survey:

Examination of all reported cases of renal stent fracture in vivo revealed an apparent trend - fracture cases appear to correlate to a higher occurence in the left renal artery than the right.  Indeed, 2/3 of cases reported in the MAUDE database are stent fractures in the left, with only 1/3 occurring in the right renal artery, suggesting physiologically higher stresses/strains imposed on stents implanted in the left renal artery. <link to paper>