In Vitro Fatigue Evaluation of Chimney Endovascular Aneurysm Repair: A Case Study


      The objective was to evaluate the positional stability and physical properties of stent grafts and covered stents that have been used in an aortic arch chimney endovascular aneurysm repair (EVAR) for a specific patient who had a thoracoabdominal aneurysm.


      An accelerated mechanical fatigue test of 120 million cycles (3 life-years) was applied to a Cook stent graft and an Atrium covered stent that were deployed inside a customized polyurethane phantom using a chimney EVAR approach. They were then mounted on an ElectroForce (TA Instruments, New Castle, Del) accelerated fatigue tester. Fabrication of the polyurethane phantoms was based on the Digital Imaging and Communications in Medicine images of the patient. The fatigued phantom with the endovascular devices inside was monitored by computed tomography scans and endoscopy views to determine changes in the size and position of the devices. Postfatigue tests including scanning electron microscopy, bursting strength, and fabric count were performed to identify any changes in the physical properties of the stent graft fabric.


      The distal angle between the chimney covered stent and the thoracic stent graft experienced significant changes during 10 to 20 million cycles (129.53 ± 2.56 degrees and 127.13 ± 1.54 degrees, respectively) compared with the control group at zero cycles (134.97 ± 2.99 degrees; P < .05). The total length of the chimney covered stent changed significantly during the first 1 million cycles from 39.33 ± 0.05 mm to 38.03 ± 0.45 mm (P < .05). The proximal angle and area, bursting strength, and graft fabric count remained stable during fatiguing. No apparent surface abrasion was observed by scanning electron microscopy.


      This chimney EVAR approach for this particular patient maintained acceptable positional and dimensional stability based on this in vitro mechanical fatigue study that mimicked a 3-year life period. These conclusions are helpful in providing clinically relevant follow-up information for this particularly challenging patient who required the off-label use of two EVAR devices.