Mitral Valve Regurgitation and Valve Biomechanics Zach Miller
Dr. Rahman (Biomedical engineering)
METHODOLOGY• IncurrentmarketstudiesItwasdiscoveredthat,“Bioprostheticvalvereplacementhas
becomeincreasinglypopular,howevercontinuestosufferfromlongevityissues.Therehavebeenexcitingadvancesininterventionalcardiaccatheterization,includingpercutaneousinsertionofthepulmonaryvalve.”(4)Areasonforthisdrivingpopularitystemsfromthefactthatheartdiseasescontinuetobethenumberonecauseofdeathwith“Valvediseaseresultinginapproximately20,000deathsannually.”(4)
•• “TheactualdirectcostforvalvediseaseintheUnitedStatesalonehasbeenestimatedat
1billiondollarsperyear.Takentogether,thepublichealthimpactofvalvediseaseandburdentosocietyisunderappreciated.Valvediseasemaymanifestas stenosis,anobstructiontooutflow,or regurgitation,adefectiveclosureresultinginbackwardflow.” (4)
•• Therearetwomajorimpairmentsthatcanoccurinthemitralvalvethatwillleadtomitral
valveregurgitation(MVr).Thefirstbeingnon-functionalvalveclosureorcoaptation inwhichthevalvesarenotcreatingpropercontactwithoneanotherandthegapbetweenthemisallowingthebackflowtooccur.ManydevicesonthemarketcurrentlytargetthistypeofMVr,somebeingthecompletereplacementofthevalvewithaprosthetic(leafletresection)andtheotherinvolvingstitchmechanismstopullmembranetissueclosertoeliminatethegapbetweenleaflets.Deviceslike….aresimilartothestichmechanism.AnothermechanismthatwasstudiedwastheMitraClip®whichusesaclipmechanismthroughintraseptal interventionwithuseofacardiaccathetertobeimplemented(minimallyinvasivebeatingheartsurgery).TheMitraClip treatmenthasbenefits,butwhenconsideringthehemodynamicandorificeareathatislostthereisstillroomforgrowthinhemodynamicabilityinMR.
•• ThesecondmethodoroperationforrepairingMVr stemsfromtheideaofchordae
tendineaerupture(CTR),inwhichthechordaetendineae(CT)arenolongerattachedtothepapillarymusclethatpreventsbackflowintotheleftatriumduringsystoliccontractionoftheleftventricle.“Whilethephysiologicalgeometryoftheleafletsandannulushavebeenpreviouslyinvestigated,littleefforthasbeenmadetoquantitativelyandobjectivelydescribeCTgeometry”Thiswillbethefocusofsomeofthefutureresearchthatisintendedtotakeplaceafterenoughmechanicaltrialshaveoccurred.OncethereisaadvancedunderstandingoftheforcesactingontheCTstructureartificialdevicescanbebetteradapttoreplicateorganictissue.Ithasalsobeenfoundthatbyusingexistingleafletandoverallmitralvalveconstructioninthiscaseismuchbetterforhemodynamics,cardiacoutputandlongevityversuscompletereplacementofthevalvewithprosthetics..“At2.9-yearfollow-up,ChordMVr forisolatedposteriormitralvalveprolapsewasassociatedwithalowreoperationrateandfavorablevalvehemodynamics,whencomparedwithleafletresection.”(5)
Primary Researcher: Zach Miller Email: [email protected]
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• Usingacollectionofdataobtainedfromdoingbiomechanicalpropertytrialsonthemocksetupforleafletconstructionwillcontributetothenextstepsofresearch.ThemainfocuswillpertaintotheconstructionofpotentialdevicesorimplementationofmethodtohelprepairMVr.ThesewilleithercomeintheformofleafletreconstructionoraprostheticchordaetendineaepossiblyinasimilarfashionasdemonstratedbyNeoChord.
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• 1.JonathanTButcher,RogerRMarkwald• Philos TransRSoc Lond BBiol Sci. 2007Aug29; 362(1484):1489–1503. Publishedonline
2007Jun14. doi: 10.1098/rstb.2007.2130•• 2.JCardSurg. 2017Mar16.doi:10.1111/jocs.13120.[Epub aheadofprint]• https://www.ncbi.nlm.nih.gov/pubmed/28303614•• 3.AnnBiomedEng. 2017Feb;45(2):378-393.doi:10.1007/s10439-016-1775-3. Epub 2016
Dec19.• https://www.ncbi.nlm.nih.gov/pubmed/27995395•• 4.AnnuRevPhysiol.2011;73:29–46. doi: 10.1146/annurev-physiol-012110-142145• https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4209403/#R17•• 5.JCardiovascSurg(Torino). 2017Jan25.doi:10.23736/S0021-9509.17.09634-3. [Epub
aheadofprint]• https://www.ncbi.nlm.nih.gov/pubmed/28124513•• 6.HeartSurgForum. 2017Feb27;20(1):E019-E025.doi:10.1532/hsf.1625.• https://www.ncbi.nlm.nih.gov/pubmed/28263146
• ThepurposeofthisresearchistofurtherunderstandthebiomechanicalstructureoftheMitralValve(MV)leafletsincombinationwiththechordaetendineaebyconductingtestsbasedonpressureandfluiddynamics(hemodynamics).“Theheartbeatsmorethan100,000timesperdayhandlingapproximately5litersofbloodperminute.Overtheaveragelifetime,therearegreaterthan3billionheartbeats,orcardiaccycles”(4)Constructingaclosedsystemdesignedtorunhighrepetitions,trackflow,maintainapressureconsistentwiththeheartiskeytounderstandinglimitationsofintracardiacdevicestorepairtheMV.“Valvetissuehasexceptionallyhighstrainbecausethetissuecyclestoacompletelyunloadedstatewitheachheartbeat.”(4)Theclosedsystemmustalsogiveabilitytochangematerialsbeingtestedastheleafletsandchordaetendineaetobestrepresentcurrenttissuedata(ofCTandleaflets).Throughuseofthisclosedsystemdevicethehopeistoexplorenewdeviceconceptsrelatingtothepotentialrepairofmitralregurgitation(MVr)andmitralvalveimpairments.TheClosedsystemusesafeebackloopthatmaintainshemostasis(equilibriumofblood)towhichextenttheforceofthechordaetendineaecanbemonitoredinunisonwiththeleafletsandseeandMVr takingplace.
•Generaloverviewofvalveanatomy•“Themitralvalveiscomposedoftwoleaflets,theanterior(oraortic)andposteriorleaflets.Thesupportingtendinouscords(chordaetendineae)ontheventricularaspectofthevalveleafletsinsertintotwowell-definedpapillarymusclesthatarecontinuouswiththeleftventricularmyocardium.Theposteriorleafletdominatesthemajorityofthemitralvalveannuluscircumference,buttheanteriorleafletislargerandmakesupagreaterarea.”(4)
•http://www.revespcardiol.org/
•Synthesisofheartvalvemechanics
•“Valvulogenesisisanextremelycomplexprocessbywhichafragilegelatinousmatrixispopulatedandremodeledduringembryonicdevelopmentintothinfibrousleafletscapableofmaintainingunidirectionalflowoveralifetime.”(1)Thisprocessiswhatgivestheleafletsahighcapacitanceofmechanicalcapabilityandallowsforproperperformanceoveralifeoftheindividual.Thisprocesscomplicatestheoverallstudyofleafletstructure,sinceit“occursduringexposuretoconstantlychanginghemodynamicforces,withasuccessrateofapproximately99%,”(1)meaningthatthereisvariabilityfromsubjecttoinleafletstructure.DefectiveValvulogenesiswillintimeresultinincreasedleafletcomplicationsthatcanfurtherevolveintohemodynamicsimpairmentsandoverallcardiacimpairment.
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