The mitral valve
The human body is a remarkable, interconnected complex of tissues, muscles, vital organs and, of course, the brain. The heart is one of those vital ‘muscles’, although unlike others it can never rest and keeps beating until we draw our last breath.
Yet, like any muscle the heart needs to be properly maintained. When we feel weak, tire quickly, are short of breath, feel pain or our feet swell, it’s telling us something which could be mitral valve disease. In short, the most common symptoms of this condition are abnormal heart rhythms and breathlessness; anyone experiencing these symptoms should seek immediate medical treatment.
The main function of the mitral valve is to allow blood to flow only in one direction from the heart’s left atrium to the left ventricle. The net of thin strings of tendinous material that we refer to as ‘chords’ (Latin: chordae) that support the valve ensures it is in the right position, however the valve must close properly at every cardiac cycle. If one or several chords ruptures, or the valve fails to close tightly enough, this will cause blood to leak backward into the left atrium putting pressure on the valve. Over time this may cause cardiac insufficiency which can only be remedied through surgery. Indeed, repairing defective valves is the most commonly performed operation by cardiac surgeons.
Where technology and medicine meet
So, what has this got to do with our scientific researchers at Vilnius Gediminas Technical University (VGTU)? A great deal, as a matter of fact because Dr. Gediminas Gaidulis from the Department of Biomechanical Engineering has developed a virtual model of the heart mitral valve that allows us to simulate damaged tissues or cardiac surgeries when the valve suffers prolapse.
Whilst further research is needed it is a most welcome breakthrough and illustrates the strong linkage between the two disciplines of medicine and biomechanical engineering. Rapid developments in new biotechnologies are being applied to the field of medicine, which in turn can be developed as a business idea and ultimately commercialised. Fundamentally, it’s about achieving more effective results in medicine by harnessing scientific innovations in other areas of research.
Mitral valve prolapse a common problem
Unfortunately, prolapse (disease) of the mitral valve is all-too common, although the good news is that it is operable. One recent estimate suggests that about 1.7 per cent of the U.S. population suffers mitral valve prolapse, with about 250,000 new patients diagnosed every year, although only 50,000 proceed to surgery. As for Lithuania, each year our surgeons perform about 200 aortic valve operations, 100 mitral valve repairs, and 100 mitral valve replacements.
Says Professor Audrius Aidietis, Head, Cardiology and Angiology Centre at the Vilnius University Hospital Santaros Klinikos:
“There are two types of mitral valve disease: valve prolapse; and valve stenosis. These diseases may be congenital or acquired. Some are born with valve defects, and sometimes problems develop over time due to various reasons.”
If the mitral valve chords rupture then serious complications occur, one of them being mitral regurgitation. For example, the mitral valve has two ‘leaflets’ that are held tightly closed by the tendinous chords. Since the heart functions as a double pump, all of the valves must be tightly closed and should open and close at the exact moment. If the chords break the leaflets will not close to form the necessary seal, causing blood to leak backward into the left atrium (chamber) in a process referred to as regurgitation. This needs to be corrected as soon as possible in order to avoid potential cardiac arrest . Even if the patient with cardiac irregularities is free of symptoms of mitral valve malfunction, clinicians consider that surgical treatment is the right course of action.
Numerical modelling and mitral valve repair
Contributing to our understanding of this medical problem is the work of Gediminas Gaidulis who recently successfully defended his PhD thesis, “Numerical modelling of transapical mitral valve repair”. His thesis is a first step in the simulation of the human cardiovascular system, the ultimate goal being to develop a more effective and technologically advanced treatment for mitral valve disease. Applying the principles of mechanics to the heart has a particular fascination for Gediminas, simply because its biomechanics are similar to the mechanical structures typically present in the field of engineering. The challenge is to adapt and apply the same methods to the properties of bio tissue.
Gediminas’ interest was sparked by an expert in numerical modelling, his thesis supervisor, prof. habil. dr. Rimantas Kačianauskas, from the Department of Applied Mechanics at VGTU. His other mentor was prof. A. Aidietis, one of the first surgeons to apply a new cardiac surgical method called transapical mitral valve repair. This operation can repair the tendinous chords of the mitral valve through a minimally invasive procedure, and without the need to stop the heart for the duration of the operation. This differs from open-heart surgery where the entire chest cavity is opened, the patient connected to a heart-lung machine, the heart stopped for about one hour, and heart and valve surgery performed. From beginning to end this procedure traumatises the patient’s body. Instead, the new type of surgery can be carried out on a functioning heart without the artificial circulation of blood. This is far safer for the patient, relatively free of complications and significantly reduces recovery time.
New surgical techniques leave the breastbone intact, with just a small incision being made at the top of the heart, through which a special tool is used to reach the organ. Ultrasound helps to locate the ruptured leaflet of a mitral valve, which is repaired with a special thread.
A new predictive model for surgical outcomes
Behind the surgery, however, sits a precise diagnosis and this is where the work of Gaidulis is important. It is vital that we understand the biomechanics of the mitral valve if we are to accurately diagnose valve prolapse, predict the further development of the disease, and treat the disease appropriately. In this regard, the numerical modelling of the mitral valve, the mathematical description of the valve’s activity and its digital simulation, shows great promise. By using a computational model we can change parameters and thereby simulate various conditions and disorders, conduct virtual tests on different valve repair methods, as well as virtual surgeries.
In the not-too-distant future this model will become a useful tool to predict the outcome of mitral valve surgical procedures. Explains prof. R. Kačianauskas:
“The developed model is where the methods of macro-mechanics are applied. In our case, one crucial task was data collection, which is easier said than done because it is far easier to work with, say, concrete or wood. We can place them in special equipment and test them, but for obvious reasons we can’t do this with the heart or other human organs. What we can do, however, is carry out calculations and draw parameters based on microstructure, because we know the structure of human cells. A human eye may see one string, but under a microscope we see the whole set of strings. The valve is like a membrane. Usually, it is depicted as one surface, but its properties are much more complicated.”
Since the geometry of a mitral valve is complicated and differs with the individual, a new model must be developed for each and every patient. In his research Gaidulis analysed two cases and developed two numerical mitral valve models based on patient-specific echocardiographic data. These were used to simulate surgeries and to evaluate the functions of a mitral valve after a transapical mitral valve prolapse repair. In both cases, following the virtual repair, the contact between the leaflets during the whole cardiac cycle was identified, and analysed if calculated biomechanical parameters are not higher than critical values.
The results look promising and while there are similar tools they are not yet used in clinical practice. More clinical cases need to be analysed and the developed methodology adapted to clinical use. At the moment the methodology is not ready to be used by doctors; the plan is to develop it further and implement the goal. More researchers from the fields of biomechanics and medicine would like to join the project. We anticipate that VGTU scientists will, following further investigation, be able to create a clinical analysis tool, allowing us to predict the outcome of mitral valve repair.
Interdisciplinary scientific collaboration
So, what does this tell us about collaboration between scientists, both at VGTU and beyond? In the sciences, experts from different fields collaborate, including engineers, mathematicians, medics, chemists, biologists, and many more. Mathematical modelling such as that being investigated by Gaidulis can be equally applied to understanding oil flows as it can to blood flows, especially through the human heart.
International collaboration offers even greater opportunities for us to cross-fertilize ideas. For example, according to prof. R. Kačianauskas:
“Recently, I participated in a conference on interdisciplinarity in Huston, and was impressed by cooperation between engineers and medics. For example, a world-class surgeon showed us how a particular surgery on the human heart is carried out. He showed the heart, described what he does as a surgeon, and at the same time how heart tissue can be simulated mechanically. It was an outstanding demonstration of knowledge in mechanics and how it is able to contribute to solving some medical problems. As engineers we need the knowledge and experience of medics to develop more effective methods of treatment. Often we do not know the needs of medics, and they in turn do not fully appreciate the huge possibilities of our research.”
In the case of VGTU, its five-year cooperation with Vilnius University Hospital Santaros Klinikos on the development of a numerical mitral valve model is a continuing success. Working alongside scientists from other disciplines breaks down communication barriers.
“Both mechanical engineers and medics have their own terminology. We are very happy that our persistent efforts took us to the level of creative cooperation. Now, we are working on joint research and publications, and expect our cooperation to become even more intensive. For example, in the area of bone or teeth prosthetics – knowledge in mechanical engineering is very important in these processes. Also I see potential in cooperation in the area of cell mechanics. If we know cell structure, then we are able to develop its mechanical model, fluid movement to and from the cell and within it,” says prof. R. Kačianauskas.
Practical research, practical outcomes, practical business collaborations
Finally, researchers and the business community often cooperate to bring scientific innovations to market, and this is something our own Research and Higher Education Monitoring and Analysis Centre (MOSTA) is keen to progress. Their recent survey shows that business in Lithuania wants to cooperate because they understand the importance of research, and especially the technological solutions they seek. Business representatives are eager for researchers to propose ideas on how they can apply and/or commercialise new knowledge, whereas researchers would like to see their technologies developed and applied through new products and services. Both parties stand to gain a great deal in terms of new knowledge and competences, and scientists are especially keen to improve their personal research results.
Comments prof. R. Kačianauskas:
“Medicine is similar to business, except that it must operate under a strict regulatory regime. The medical industry is based on patents, and surgery technologies must be approved. A place in the global market can be earned only if we can offer ideas and innovations in engineering that are relevant in that context. A productive cooperation between research and business is a must, and interdisciplinary research deserves to gain more attention. To create true interdisciplinarity we must break down the barriers that exist between different institutions.”
