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The Journal of Cardiovascular Surgery 2000 April;41(2):193-202


lingua: Inglese

Patterns of systolic stress distribution on mitral valve anterior leaflet chordal apparatus. A structural mechanical theoretical analysis

Nazari S. *, Carli F. **, Salvi S., Banfi C. *, Aluffi A., Mourad Z., Buniva P., Rescigno G. ***

From the *Foundation Alexis Carrel°, Pavia, Italy Department of Surgery, IRCCS San Matteo University of Pavia, Pavia, Italy **Department of Structural Mechanics University of Pavia, Pavia, Italy ***Centre Cardiologique du Nord, St. Denis, Paris, France


Increasing dif­fu­sion and com­plex­ity of ­mitral ­valve ­repair pro­ce­dures may ­prompt an inter­est in the eval­u­a­tion of the pat­terns of ­stress dis­tri­bu­tion on the ­chords, ­which are, ­from the struc­tu­ral mechan­i­cal ­point of ­view, the weak­est ele­ment of ­valve appa­ra­tus. This theo­ret­i­cal anal­y­sis con­cen­trates in par­tic­u­lar on the ­mitral ­valve ante­ri­or leaf­let. As is ­known, the ­vast major­ity of the chor­dae are ­attached to the ante­ri­or leaf­let with­in the coap­ta­tion ­area; dur­ing sys­tole ­they are ­then nec­es­sar­i­ly par­allel, ­aligned ­along the ­same ­plane as ­that of the ­leaflets’ coap­ta­tion sur­face, to ­which ­they are ­attached; more­over the thick­ness of the chor­dae increas­es sig­nif­i­cant­ly ­from the mar­gi­nal chor­dae to the ­more cen­tral ­ones. In nor­mal con­di­tions dur­ing sys­tole the pro­gres­sive­ly wid­er coap­ta­tion sur­face caus­es the increas­ing ­stress to be sup­port­ed by an increas­ing num­ber of pro­gres­sive­ly thick­er ­chords, ­which are sub­stan­tial­ly par­allel and ­aligned on the coap­ta­tion sur­face ­plane in ­such a way ­that ­they can ­share the ­stress ­between ­them, accord­ing to ­their thick­ness; in oth­er ­words ­chords ­form a mul­ti­fil­a­ment func­tion­al ­unit ­which ­enrols ele­ments of increas­ing thick­ness in ­response to the mount­ing ­stress. The geo­met­ri­cal mod­ifi­ca­tions of the ­valve appa­ra­tus archi­tec­ture (annu­lus dil­a­ta­tion, leaf­let retrac­tion, chord­al elon­ga­tion or retrac­tion) ­often asso­ciat­ed ­with ­valve insuf­fi­cien­cy due to chord­al rup­ture, ­have the com­mon ­result of caus­ing, dur­ing sys­tole, a radi­al dis­ar­range­ment of the direc­tion of ­most of the sec­on­dary chor­dae ­which are no long­er par­allel, ­aligned on the coap­ta­tion sur­face ­plane. Due to the neg­li­gible elas­tic mod­ule of the ­valve leaf­let, in ­this new arrange­ment the var­i­ous chor­dae can­not ­share the ­stress ­between them­selves as ­they do in a nor­mal phys­io­log­i­cal sit­u­a­tion; on the con­trary the thin­ner chor­dae near­er to the ­free mar­gin are ­also load­ed ­with the ­peak sys­tol­ic ­stress, ­thus gen­er­at­ing con­di­tions favor­ing ­their rup­ture. It can, there­fore, be hypoth­e­sized ­that the ana­tom­o­path­o­log­i­cal pic­ture of ­valve insuf­fi­cien­cy due to chord­al rup­ture may be the ­final ­event of a ­series of geo­met­ri­cal mod­ifi­ca­tions of ­valve appa­ra­tus archi­tec­ture, the com­mon con­se­quence of ­which is to ­load thin­ner mar­gi­nal ­chords ­with ­peak sys­tol­ic ­stress ­from ­which ­they are nor­mal­ly ­spared, ­thus favor­ing ­their rup­ture.

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