Surgical and transcatheter heart valve replacement and repair devices require in vitro durability testing under accelerated conditions to mimic the in vivo lifetime use. Our cardiovascular device testing experts are ready to assist with the validation of your devices so that you can bring safe and effective products to patients worldwide.
Degenerative heart disease, calcification, congenital abnormalities, and infections are some of the causes of heart valve disease. Aortic and mitral valves may become stenotic or regurgitant, requiring replacement or repair. Transcatheter valve replacement or repair has been gaining traction replacing some surgical procedures with implants typically delivered either through percutaneous transfemoral or transapical access.
Element routinely characterizes heart valve prostheses using test methods tailored to the devices and their design. Applicable standards include ISO 5840, ISO 5910, ISO 7198, ISO 25539-1 and ASTM F2477.
Heart valve durability testing
In vitro durability testing of transcatheter heart valves, by replicating in vivo conditions through mechanical fatigue, is a critical implant characterization step. We evaluate full devices and stent strut or support structures under accelerated conditions, simulating physiological strain for 10 to 15 years post-implantation.
Our transcatheter mitral valve axial fatigue testing article discusses the test protocol used for heart valve repair device components.
Stent strut fatigue testing (S-N curve generation)
In the case of stented valves, the stent portion of the device is often tested separately. Stent strut fatigue evaluates the high-strain portion of the stent or valve support structure. The test specimen may be either a representative geometry such as a stent coupon, or stent segments harvested from a post-processed device. Test specimen geometry is typically determined using finite element analysis (FEA).
To perform the test, our experts place a strut apex or other representative geometry on an axial fatigue tester using special fixturing to apply cyclic tension/compression. We can customize the test fixture to accommodate the specimen geometry, and typically 12 to 15 samples are tested simultaneously.
Additionally, we perform load monitoring to help detect specimen failures and ensure that the specimen reaches the desired load throughout the test. This data is then used to generate SN curves (stress vs. number of cycles).
Heart valve frame fatigue
Many bioprosthetic valve designs include a support frame to facilitate implantation. The frames are typically laser-cut nitinol, braided wire, or most recently made from bioabsorbable polymers. We evaluate the stented frame of these valves with pulsatile fatigue loading for 400M or 600M cycles.
The test method deploys the stent inside a mock vessel with physiologically-relevant compliance and hydrodynamic pressure. It is important to ensure that the mock vessel geometry follows the stent design for proper apposition and fatigue loading.
During heart valve frame testing, physiologically-relevant vessels are often used to determine target strains for a given device, and then thick-walled vessels are used for the fatigue test. The thick-walled mock vessels allow us to run the stent-graft tester at higher frequencies, thereby reducing overall test time.
To learn more about this test method, read our stent pulsatile durability testing article.
Device acceptance & failure criteria
Manufacturers typically define the criteria for device failure or acceptance. Criteria for failure can include loss of continuity for the stent strut test, or any broken or cracked strut visible at 30x magnification during or at the end of the full device test. After testing, device manufacturers examine the specimens against their predefined criteria.
Element uses ElectroForce 3200 and 3300 test instruments for stent strut fatigue tests coupled with several inspection methods including:
- High-speed video
- Strobe light
For more information about our heart valve device testing services, or to request a quote, contact our experts today.
The main applicable heart valve test standards are:
- ISO 5840-1 Cardiovascular implants – Cardiac valve prostheses – Part 1: General requirements
- ISO 5840-2 Cardiovascular implants – Cardiac valve prostheses – Part 2: Surgically implanted heart valve substitutes
- ISO 5840-3 Cardiovascular implants – Cardiac valve prostheses – Part 3: Heart valve substitutes implanted by transcatheter techniques
- ISO 5910 Cardiovascular implants and extracorporeal systems – Cardiac valve repair devices
If the valve is stented to support the leaflets, the following standards apply for testing the stent portion of the device:
- ASTM F2477 Standard Test Methods for in vitro Pulsatile Durability Testing of Vascular Stents
- ISO 25539-1 Cardiovascular implants – Endovascular devices – Part 1: Endovascular prostheses
- ISO 7198 Cardiovascular implants and extracorporeal systems – Vascular prostheses – Tubular vascular grafts and vascular patches
Transcatheter Mitral Valve Axial Fatigue Testing
While pulsatile durability testing is often the primary test that comes to mind, axial fatigue testing of valve repair components serves as a very useful tool in characterizing the durability of individual devices.
Stroboscope Visual Inspection of Medical Devices
Digital stroboscopes facilitate visual inspections of cardiovascular medical devices as they undergo accelerated fatigue. The strobe light is a very useful tool in detecting device failures and tracking motion during testing.
Stent & Graft Testing
Element’s cardiovascular device experts offer a comprehensive suite of stent and graft testing including pulsatile durability, fatigue, visual inspection, and custom test methods.
Electrochemical Corrosion Testing
Element performs electrochemical corrosion testing per ASTM F2129 to ensure that medical devices are safe, and provided the intended benefits to the patient.