PERCUTANEOUS AORTIC
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`VALVE REPLACEMENT
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`I. Anatomyy‘é,
`The aortic valve is a structure whose function is to direct the flow of blood from the left ventricle
`into the systemic circulation through the aortic artery.
`11 accomplishes this function by opening during the
`contraction of the left ventricle and closing when the left ventricle relaxes. The aortic valve is a tricuspid
`structure and each cusp folds up toward the aorta during the contraction phase and then fold back against
`each other in the relaxation phase. (figure 1 show a picture) However, the aortic valve is a complex
`structure with integral relationships beyond merely a three leaflet valve. For instance, each leaflet sits
`directly opposite an outpouching of the proximal aorta. This dilated segment is called the sinus of valsalva,
`and it is this anatomic relationship that assist the valve to open and close repetitively while minimizing the
`stress upon any point within this valvular apparatus. Further, the proximal porion of the aortic valve is
`highly elastic and with this elasticity it can dilate during the contracion phase of the left ventricle.
`Historically, it has been theorized that this reduces the amount of work that the left ventricle performs. As
`with anything in nature it is much more complex. The valvular structures are integrally related to the
`coronary arteries. The function of the coronary arteries are to supply blood supply to the heart. Thcse, as
`' /
`represented in figure 2, are located within 2 of the sinuses.
`In a normally functioning valve, the cusps
`open widely to allow the unimpeded transference of blood, and then closetightly not allowing any‘Ft‘ow '0 /° 3'
`regurgitate back into 1.119163% ventricle. When there is significant restriction to blood flow, this is called
`stenosis and when it alld‘ws‘ blood back into the left ventricle it is regurgitation. Thus. each component
`plays a vital role in the function and durability of the valve.
`Interestingly, the
`The first components of the valve I would like to discuss are the leaflets.
`number of the leaflets within a normal aortic valve does not vary to a significant degree. When there are
`less than three valves, the valve undergoes rapid stenosis and restriction. Among congenital alterations
`upon the valve number the most frequently encountered is a bicuspid aortic valve. This condition is the
`most common defect that is survived into adult hood. However, this valve predictably becomes more and
`more stcnotic and regurgitant by the 41]] and 51h decade. Unfortunately, this usually results in the need for
`surgical replacement. A unicusped valve rarely survives beyond the first year of life. (figures 3 and 4).
`Rarely a quadricusped valve will be shown to survive into adulthood. This design also results in marked
`stenosis.
`Further, the cusps are shaped in a defined convexity. This design permits the dispersion of
`pressure over a larger surface area. This dispersion resists the exhaustion of the valve in any one particlular
`place. Moreover, this curvature allows the leaflet to reverse curvature. An ability needed in order to fold
`and allow the maximum opening diameter during contraction. Finally, a curved design allows a
`redundancy in the coaptation site of the leaflets. The area of coaptation is the edge of the valves that must
`meet and close in order for there not to be regurgitation. chcc, both the number of leaflets and their
`overall shape is important in the function and durability of the valve.
`As mentioned earlier, the valve leaflets have a direct relationship to the sinus’s of valsalva. The
`sinus diameter is almost twice that of the aorta. This cavity plays an important role in the mechanism of
`valve closure (referenced Mano Thubrikar). An oblique section through the leaflet—sinus assembly shows
`this remarkable relationship. (figure4) . This section reveals that the sinus and leaflet form a circle when
`the valve is in a closed position. Furthermore, it is angulatcd to a degree as to allow pressure transduction
`along the entire surface of this unit. This suggest that the shape of the leaflet-sinus assembly is important I
`determining 110w stresses are developed within the valve.
`It is also this relationship that allows the valves
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`to close without pulling upon the aortic valve as has been suggested. Finally, this relationship Quilt; ,_
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`sinuses and valve allow for the efficient flow of blood in'the coronary ostia.
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`The aortic root has been described to expand during ventricular contraction. @he dilatatioifi of this
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`f, (- m 1.1m;
`structure by the {law offlaplace reduces tension which in turn reduces resistance to flow.
`It is this
`.......[311611911213111.1413er 211593111926 fgyrpgniplete opening of the aortic valve.
`lnterestinglwvhen the cusps open
`Sam is maintainedza circularkkdiritensionlthatvisatleasatheeameasbeforeeomraction. Moreover, it)5 has
`been studied to be evenlarger'than the original orifice. (Medical Engineering & Physics l9(8):696-
`710,1997).
`In more detail,
`this behavior allows the valve to have reduced circumferential stress and a
`reduced Rcynold’s shear stress number. This is the number used to evaluate the amount of stress in a
`confined fluid system.
`ln a similar manner,
`the inner lining of the cusp of the valve, the lamina
`ventricularis extends into the ventricular myocardium. There is a confluence of fibers at the base called the
`fibrous coronet which is a distinct seéelation between the elastic fibers above and the myocardium below.
`However,
`this structure is not static.
`In contrastjit is a very dynamic structure which bends and molds to
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`NORRED EXHIBIT 2040 - Page 1
`Medtronic, |ne., Medtronic Vascular, Inc.,
`& Medtronic Corevalve, LLC
`
`v. Troy R. Norred, MD.
`Case |PR2014-00110
`
`

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`the forces which are exerted from the ventricular 111yoc11rdium (Cardiovascular
`Research22 7 1988)(Jour11al of Biomcchanics33(6):653—658 2()0()June)
`111 11 similar fashionas the aortic /
`root this structure allow the valvular apparatur to open with the least amount of sti.ain
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`The cmonary arteries arise within 01 above theQnus ofv}11salva. The blood flow ofthe heart
`occurs mostly when the ventricle relaxes At this 111116116 cusps of the aortic valve are closed and as
`mentioned the diastolic forces of the blood against the valve are dispersed along the valve 11nd adjacent
`sinus. The opening or ostia of the coronary arteries when located near the apex 11nd middle of the sinuses
`allows for the most laminar flow characteristics. This111 turn promotes the greates>amount of flow with the
`least amount of 1esistance ln disease statcsjwhere these relationships are lost it 1111s been proposed that
`this could lead to increase sticss at the corona1y ostia (The A01tic Valve CRC press).
`These integral relationshipinot only pertain to the gross anatomy of the valvular apparatus but
`alsothe microanatomvshewfihefiegmhmtumfflesemuettwes.JThe amount of elastinIS in a higher
`concentration as shown by staining methods (American Journal of Pathology 445 (7): 193.1). This allows a
`greater amount of dilatation of the structures in this area. Further, scanning electron micrographs have
`shown the unique arrangement of collagen in the valves which permit the unique reversal of curvature
`which is vital in the function of the valve (figure 6)( Anatomic Embryology 172(61): 1985). The fibers are
`unusually small and arranged in sheets with unique distances between each strand. In theory,this would
`give 11 greater amount of tensile strength while allowing continued flexibility. As always, nature 1111s
`selected the most efficient machinery, and we have only to discover the reasons why.
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`11.
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`Aortic Valve Dynamics and Physics
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`The aortic valve is better understood in a dynamic state given it is not a static structure. To fully
`understand this structure it is integral to understand the opening and closing of the valve. the motion of the
`various parts? the design of the valve in vitro 11nd the hydrodynamics of the valve. The valve’s ultimate
`function is to allow fluid transfer from the ventricle to the systemic circulation.
`[11 order to do this
`effic1ently it minimi7cs shear stless resistance to flow and tensile for.ces
`The opening and closing of the aortic valve depends upon differential p1essures flow velocity
`characteristicsand as mentioned earlier Jthe unique anatomic relationship between the valves and the 1112»«1:31J11, 11
`@iirusesof»%1
`v11 One of the most compiehensivc studyeeneompassed a model developed by Bellhouse J
`et al.
`In this model,
`the flow of fluid through the aortic valve was studied by injecting dye within the flow
`of fluid.
`Some of the pertinent observations found within this model were as follows: 1) The valve opens
`rapidly, and as the leaflets move into the sinuses, vortices form between the leaflet and the sinus walls; 2)
`The flow enters the sinus at the sinus ridge, curls back along the sinus wall and leaflet and then back into
`the main stream; .3) During the end of systole the vorticcal motion created during contraction forces the
`valves back toward a closed position. These observations are 1111p01tant to show that absolute p1essure
`differences created between the aorta and ventricle are not the source of initial closure of the aortic valves.
`In fact,
`it would be detriminal to valve stress if these f01ces dictated closure of the aortic valve.
`F01
`example, if two objects are 11 greater distance apart and a set amount of force is applied to each, the greater
`distance would produce greater velocity and the momentum at impact would be greater. Therefore, if the
`leaflets are closed or near closure as contraction is coming to 1111 end then the force used for coaptation
`would be less. Less force per cycle equates to greater longevity of the valve.
`In conclusion, the cusps 11nd
`the relationship of closure for prosthetic valves must incorporate passive closure during systole which
`would logically lengthen the lifespan of any such device.
`To expand these concepts. the theory of laminar flow and 110w the native aortic valve
`accomplishes this must be developed. A laminar flow is predicted by 11 Reynolds number which
`incorporates the laws as described by Pouiselle and Bernoulli.
`111 generaL the lower the
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`NORRED EXHIBIT 2040 - Page 2
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