In the specialized field of cardiovascular medicine, delicate surgeries like heart valve replacements have saved countless lives. Thanks to advancements in medical technology, these procedures have evolved tremendously over the past decades. One such evolution is the use of bileaflet valve prostheses in mitral valve replacement surgeries. A bileaflet valve is a type of mechanical heart valve with two semi-circular leaflets that open and close with each heartbeat, allowing blood to flow in one direction through the valve. A groundbreaking study published in the Journal of Cardiothoracic and Vascular Anesthesia has delved into the specifics of how the design and orientation of bileaflet valve prostheses impact the dynamics of intraventricular blood flow, providing insights that could lead to significant improvements in patient outcomes.
In the study, “Bileaflet Prosthesis Design and Orientation Affect Fluid Shear, Residence Time, and Thrombus Formation” (DOI: 10.1053/j.jvca.2019.03.018), researchers from the Bioengineering Program, Department of Mechanical Engineering at San Diego State University, led by Vu Vi V and Karen May-Newman, made key observations about the intersections of engineering and medicine. Their research showed that the combination of the anatomic orientation and gap size of the St. Jude Medical valve design specifically could lead to increased shear exposure and blood residence time. These factors are particularly important as they both predispose the formation of thrombus—a blood clot—in the high shear gaps of the valve hinges.
Anatomy and engineering come together in this delicate balance where the orientation of the bileaflet valve prosthesis can significantly affect the intraventricular flow patterns. If the leaflets are not positioned correctly or the gap size between the leaflets and the valve ring is too small, the result can be higher levels of fluid shear stress. Fluid shear stress is a form of friction between layers of fluid moving at different speeds. In the human body, this stress acts on blood cells as they move through blood vessels or heart valves.
When the shear levels are elevated for an extended period, it can cause damage to the blood components and encourage the development of blood clots. For patients with mechanical heart valves, these blood clots can be particularly dangerous as they can lead to valve thrombosis, obstructing blood flow, or even break free and cause a stroke or heart attack.
Furthermore, the study highlighted the significant role of blood residence time—how long the blood spends within the nooks and crannies of the valve mechanism. Longer residence times increase the risk of thrombus formation because static blood is more prone to clot than moving blood. The St. Jude Medical valve’s small gap size contributes to this increased residence time, thus heightening the risk of thrombus formation.
The clinical implications of these findings are profound. Mitral valve replacements are common for conditions like mitral valve stenosis or regurgitation, where the natural valve does not function correctly. Mechanical valves are known for their durability, making them an attractive option for younger patients who require valve replacement, often as a result of rheumatic heart disease.
However, this study sheds light on a critical issue: the potential for thrombus formation and the consequential health risks involved. As such, the research serves as a call to action for both the bioengineering and medical communities to refine the design and implantation techniques of bileaflet mechanical valves. By exploring alternative orientations or modifying the gap sizes within the leaflets’ design, there is potential to significantly reduce the shear stresses and residence times experienced by the blood.
Given the study’s findings, it’s clear that cardiologists, surgeons, and device manufacturers must consider the mechanical fluid dynamics of heart valve prostheses with great care during both the design and surgical implantation phases. This interdisciplinary approach to cardiovascular treatment is the only way to ensure the highest level of patient safety and long-term health outcomes after heart valve replacement surgery.
The study hails the importance of cross-disciplinary research, where bioengineers and medical professionals collaborate to bridge the gap between theoretical engineering concepts and clinical practice. By understanding the mechanisms of fluid dynamics within the cardiovascular system, the research can then be translated into more effective and safer prosthetic heart valve designs.
While mechanical bileaflet valves are known for their longevity compared to biological valves, they generally require patients to take anticoagulant medications for life to prevent thrombosis. This lifelong dependency on blood thinners comes with its own set of challenges and risks, such as increased chances of bleeding. Consequently, advancements that could reduce the thrombogenicity of these devices would not only improve safety but could also potentially reduce the reliance on these medications, enhancing the patient’s quality of life.
Moreover, the study stresses the need for personalized approaches in selecting and implanting prosthetic heart valves. What works for one patient may not be optimal for another due to individual anatomical differences and variations in blood flow characteristics. Personalized medicine in this context may involve computational modeling to predict the blood flow patterns specific to a patient’s heart anatomy, leading to tailored surgical strategies for valve placement.
Lastly, research like this exemplifies why ongoing innovation in cardiovascular bioengineering is vital. It is the pathway to improving medical devices that have already revolutionized treatment, ensuring that future patient outcomes are even better. With enhanced designs and precise orientations aimed at minimizing fluid shear and residence time, the hope is that the next generation of bileaflet valve prostheses will set a new standard in cardiac care.
References
1. Vu Vi V, May-Newman Karen K. Bileaflet Prosthesis Design and Orientation Affect Fluid Shear, Residence Time, and Thrombus Formation. J Cardiothorac Vasc Anesth. 2019 Oct;33(10):2870-2872. DOI: 10.1053/j.jvca.2019.03.018
2. Pibarot P, Dumesnil JG. Prosthetic heart valves: Selection of the optimal prosthesis and long-term management. Circulation. 2009;119:1034-1048.
3. Duraiswamy N, Schoephoerster RT, Moreno MR, Moore JE. St. Jude Medical Valve: Magnitude and Reversal of the Prosthesis Mismatch Effect with Size. J Heart Valve Dis. 2007;16(5):455–61.
4. Sacks MS, Smith DB, Hiester ED. The aortic valve microstructure: Effects of transvalvular pressure. J Biomed Mater Res. 1998 Aug;41(1):131-41.
5. Bluestein D, Rambod E, Gharib M. Vortex shedding as a mechanism for free emboli formation in mechanical heart valves. J Biomech Eng. 2000 Apr;122(2):125-34.
Keywords
1. Heart Valve Prosthesis
2. Thrombus Formation
3. Bileaflet Valve Orientation
4. Cardiovascular Bioengineering
5. Mitral Valve Replacement
The implications of this study are clear; as the intersection of cardiovascular medicine and bioengineering continues to evolve, patient-specific surgical planning and device tailoring emerge as crucial components in the quest for enhanced heart valve replacement outcomes.