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Designing Safer Bioprosthetic Heart Valves With CFD-PIV

University of California Researchers use Tecplot 360 CFD visualization software to help identify vortex abnormalities.

In 1960, Dr. Albert Starr successfully implanted the world's first prosthetic heart valve, a mechanical device that he co-invented with M. Lowell Edwards, a prominent engineer. More than 50 years later, lives of millions of patients have been saved or improved by technological advancements based on the work of pioneers like Dr. Starr, Edwards, and others. Today, more 250,000 patients worldwide receive prosthetic heart valves annually, and that number is growing.

Yet, there remains more work to be done. Patients who underwent heart valve replacement experience a better quality of life. However, complications can occur due to the result of the device’s failure, structural valve deterioration caused by infection, the valve’s design or materials, or host tissue overgrowth.

Ahmad Falahatpisheh a Ph.D. candidate at Kheradvar’s lab (KLAB) at the University of California, Irvine, is at the forefront of pioneering research in the area of artificial heart valve development to improve bioprosthetic heart valves and the quality of life of patients. With the help of Tecplot 360 CFD visualization software to view and analyze his Digital Particle Image Velocimetry (DPIV) data, Falahatpisheh is helping develop the first bileaflet bioprosthetic mitral valve with dynamic saddle annulus designed to mimic the natural mitral valve.

Flow features such as vortices developed through this valve are very similar to its natural counterpart. In addition, stress at the tip of the leaflets, which can cause leaflet damage is much less than the valves with rigid annulus. This is mainly due to the dynamic annulus made of Nitinol which adapts itself to the motion of the cardiac base in the heart cycle.

The result of this exciting research is to appear in the Journal of Heart Valve Disease.

Making Safer, More Efficient Prosthetic Heart Valves 

There are two types of artificial valves available today: mechanical or prosthetic valves, like the Starr-Edwards device; and biological valves made from tissue material, also known as bioprosthetic heart valves. Both have advantages and disadvantages. Biological valves reduce the risk of blood clots, but wear out and usually require replacement within 10 to 15 years in older patients, much sooner in younger patients.

Mechanical valves are durable and can last a lifetime, but can cause blood clots with life-threatening consequences, and therefore require patients to take blood thinners throughout their lives.

Most research today is focused on bioprosthetic heart valves because they cause fewer side effects. They can create close to natural flows compared to mechanical heart valves. If researchers can figure out how to make them last longer, in most cases, they would be a better replacement option for patients.

Heart valves tend to calcify around the tip potentially as a result of excessive stress. The calcification can lead to fatigue, tearing, and ultimately valve failure if the valve is not replaced. By reducing the stress and subsequent calcification, researchers can improve the longevity of the valve.

In particular, Falahatpisheh has been evaluating bioprosthetic heart valves assembled in an artificial heart flow simulator to examine the transvalvular flow with the help of high-speed DPIV technique. Using Tecplot 360, he is able to visualize the data related to the flow passing through a valve and identify potential anomalies, clearing the way for the design and development specifically for  their dynamic, bileaflet mitral bioprosthesis heart valve.

Leveraging High-Speed PIV to Develop Prosthetic Heart Valves

As with any medical device that is implanted in a patient, a crucial step in its development is to ensure that the device successfully passes a stringent set of standards.

“The flow features of a prosthetic heart valve are very important. It’s not only the solid design. You know you can test the valve with a fatigue test and determine that it’ll last a long time, but if you don’t get the correct flow features, it’ll affect the efficiency of the heart,” said Falahatpisheh. “The artificial heart valves shouldn’t cause the heart to work less efficient in order to pump the same amount of blood.”

As a quality control step, Falahatpisheh employs DPIV and CFD to assess the flow passing through the valve. Using these techniques, he can determine the extent that the artificial valve is mimicking the natural valve and ensure they are compliant with the standard guidelines.

“The use of high-speed PIV (1000 fps) at KLAB is unique and to our knowledge, no one else is doing this for the heart valves at this temporal/spatial resolution,” notes Falahatpisheh.

PIV research on heart valves assures physicians and the FDA that the heart valves to be implanted in a patient will operate safely, correctly and for a longer period of time. To conduct his PIV studies, Falahatpisheh illuminates fluorescent micro particles on the plane he is interested in gathering data on. From there, he takes 1,000 images per second in order to visualize the flow field.

“The beauty of this system is that it’s a high-speed PIV with 1,000 velocity frames per second,” said Falahatpisheh. “In the past, people could only take images at about 15 frames per second. Our current time resolution is very tiny, one millisecond, which enables us to obtain results that are extremely accurate.”

The Role of CFD Methods & Visualization in the Development of Prosthetic Heart Valves

The use of CFD to study artificial heart valves is the research of many scientists. It gives insights to the details of the flow which can be beneficial to the heart valve design process.  The challenge is to implement the proper boundary conditions which may lead to deviation from the physical and realistic solution. However, by using DPIV technique and artificial heart flow simulator at KLAB, any pulsatile flow similar to the blood flow inside the body can be experimentally produced, eliminating the difficulty of implementing the boundary conditions using CFD.

Falahatpisheh imports DPIV data to Tecplot 360 to obtain streamlines, which are essential for identifying abnormalities in the flow. This enables Falahatpisheh to visualize the streamlines, see how the flow is structured and moves through time, and gather related information.

Falahatphisheh uses Tecplot 360 to look at the vortex patterns and identify valve dysfunctions to help diagnose between a normally functioning heart valve and an abnormal valve. The analysis at this stage is critical: it is essential that an asymmetric vortex pattern is achieved within the flow through the valve. If it shows a symmetric pattern, it means the flow pattern is not optimized to properly transfer the momentum and energy from the heart chamber to aorta.

Tecplot 360 helps Falahatpisheh identify these flow abnormalities, and determine how and where to alter the design to ensure a proper flow pattern. If this portion is inaccurate, all the work and research that takes place after the tests will also be inaccurate.

Technology Enabling the Development of a Longer Lasting Artificial Valve

As technology continues to advance, so will advancements in medicine that make an even greater impact on patients, medical professionals, and manufacturers in the medical field.

Falahatpisheh’s research and use of Tecplot 360 to detect vortex abnormalities will further revolutionize the advancements first led by Dr. Starr and Edwards more than a half-century ago, by designing a dynamic, bileaflet mitral bioprosthesis heart valve to hopefully last the patient’s lifetime. The end goal of his research is to aid in the development and production of a safer, better bioprosthetic heart valve that help physicians save more lives, and improve the quality of life for many others.

Ahmad Falahatpisheh is a Ph.D. candidate in the mechanical and aerospace engineering department at the Edwards Lifesciences Center for Advanced Cardiovascular Technology at the University of California, Irvine. His current research project is focused on the assessment of mechanical behavior and optimization of a bi-leaflet bioprosthetic mitral valve by using Finite Element Analysis and Digital Particle Image Velocimetry.