Left Ventricular Outflow Tract Obstruction

Transcription

1 review rticle Left Ventriculr Outflow Trct Ostruction Ostrucción del trcto de slid del ventrículo izquierdo Revist Colomin de Rdiologí Volumen 28 No. 1 Mrzo de 2017 Alejndro Zulug Sntmrí 1 Ntli Aldn S. 1 Crolin Gutiérrez M. 2 Sestián Bustmnte Z. 2 Pul C. Muñoz G. 3 Nicolás Zulug M. 3 Key words (MeSH) Mgnetic resonnce imging Hert Hert ventricles Summry The left ventriculr outflow trct (LVOT) is the ntomic structure through which the left ventriculr stroke volume psses towrds the ort. The LVOT consists of three components: suvlvulr component, which is delimited y the memrnous nd sl musculr portions of the interventriculr septum; vlvulr component (the ortic vlve); nd suprvlvulr component. This cdemic review evlutes different ostructive pthologies of the LVOT, including entities locted t the ortic vlve level (vlvulr), in the scending ort (suprvlvulr), nd in the proximl portion of the LVOT (suvlvulr). Plrs clve (DeCS) Imgen por resonnci mgnétic Corzón Ventrículos crdicos Resumen El trcto de slid del ventrículo izquierdo (TSVI) es l estructur ntómic trvés de l cul sle el flujo sistólico del ventrículo izquierdo (VI) hci l ort. El TSVI está conformdo por tres componentes: suvlvulr, el cul es delimitdo por el septo interventriculr en sus porciones memrnoss y musculr sl y l vlv nterior de l válvul mitrl; el componente vlvulr, corresponde l válvul órtic, y el suprvlvulr. En est revisión cdémic se evlurán ls ptologís ostructivs del trcto de slid del ventrículo izquierdo, incluyendo entiddes loclizds en el sector vlvulr órtico (vlvulres), en l ort scendente (suprvlvulres) y en el trcto de slid del ventrículo izquierdo proximl l plno vlvulr (suvlvulres). 1 Rdiologist, Centro Avnzdo de Dignóstico Médico (CediMed). Medellín, Colomi. 2 Rdiologist resident, Universidd Pontifici Bolivrin. Medellín, Colomi. 3 Rdiologist resident, CES university. Medellín, Colomi. Suvlvulr ostruction The suvlvulr left ventriculr outflow trct (LVOT) is delimited y the interventriculr septum in its sl memrnous nd musculr portion nd firous continuity tissue etween the ortic vlves nd the mitrl vlve (nterior vlve to the mitrl vlve). Through these structures psses the systolic flow of the left ventricle efore reching the ortic vlve. Both components re highly moile so the suvlvulr LVOT re my e modified during the crdic cycle (1). Aortic suvlvulr ostruction my e the consequence of different pthophysiologicl mechnisms: dynmics, such s those tht cn present fter mitrl nd ortic vlve surgery; mixed, s usully occurs in hypertrophic crdiomyopthy nd mechnisms in which fixed ntomicl sustrte previls s in the memrnes or the diphrgms. Hypertrophic crdiomyopthy (HCM) The ccepted clinicl definition for HCM is left ventriculr (LV) hypertrophy ssocited to non-dilted ventriculr chmer, condition tht cn t e explined y hert or systemic disese (2-5). HCM is cused y muttions in the genes encoding crdic srcomeres proteins. It is n utosoml dominnt disese with vrile expression nd penetrnce. The usul morphologicl phenotype is the thickening of the wll of the left ventricle. However, ecuse of the multiplicity of genetic muttions nd their trnsmission, the crdic in- Rev. Colom. Rdiol. 2017; 28(1):

2 Revist Colomin de Rdiologí volvement my vry nd rrely ppers with norml wll thickness of the LV or with compromise of the right ventricle (RV) (4). Accepted dignostic criteri for HCM consist of mximum wll thickness of LV 15 mm nd rtio etween the thickness of the septl wll nd tht of the lower wll higher thn 1.5. In children, thickness of the wll 2 stndrd devitions ove the men (score z 2) is used (6). The clinicl presenttion of HCM is vried nd in ll ge groups, the mjority of ptients hve norml life expectncy without disility or need for myor therpeuticl procedures. When mnifesttions occur clinicl symptoms usully come in three forms: sudden deth due to mlignnt rrhythmis (more common in children under 35 yers nd thletes), hert filure with exertionl dyspne nd proxysml or chronic tril firilltion (6). The HCM hs different sutypes: septl, symmetric, midventriculr, picl nd concentric, mong others (7,8). The mechnism cusing ostruction of the outflow trct of the LV t the HCM is mixed: 1. Antomicl sustrte Protrusion of the hypertrophic sl interventriculr septum towrds the exit trct (figure 1). Anomlies of the vlvulr nd suvlvulr mitrl pprtus, including elongted mitrl vlves, smll mitrl nnulus or endocrdil thickening of the ventriculr surfce of the nterior vlve (9). Suvlvulr normlities include hypertrophy nd vrints in the ppillry muscles, which cn e ifid or hve vrition in the numer of implnttion, s in the cse of short tendon cords or direct insertion of the ppillry muscles in the mitrl vlves (10). The nterolterl displcement of the ppillry muscles my contriute to the ostruction of the outflow trct. These ltertions my produce ostruction even in ptients with ventriculr wll thickness very close to norml (11,12). 2. Proposed dynmic mechnisms Protrusion of the hypertrophic septum genertes ccelertion of flow in the LVOT nd reduction of lterl pressure, triggering venturi effect tht ttrcts the nterior vlve of the mitrl vlve nd cuses it to contct the interventriculr septum ccentuting the ostructive effect. This phenomenon is known s systolic nterior movement (SAM) of the nterior vlve of the mitrl vlve (Figure 1 nd d). When SAM is present, it produces flow of mitrl insufficiency (13-16). The second mechnism suggests n norml ventriculr morphology with n unusul reltionship of the output nd input trcts of the LV. A decrese in the ortomitrl ngle of projection projects the vlvulr nd suvlvulr mitrl pprtus to the LVOT exposing the vlve of the mitrl vlve to the outflow of the LV nd fvoring its displcement (13). Recently it hs een proposed tht the ortoseptl ngultion in the projection of three chmers is importnt in the ostruction of the LVOT nd cn e used s predictor of inducile ostruction in symptomtic ptients who do not hve significnt grdient of the resting trct t rest (13,17). The ortoseptl ngle is defined s tht formed etween line drwn long the order of the left nd right interventriculr septum nd line long the longitudinl xis of the ortic root. A vlue of 180 represents stright line from the septum to the ort nd lower vlues indicte n increse in ngultion. In the study conducted y Critoph et l., ptients with HCM hd lower ortoseptl ngle thn controls (113 ± 12 vs. 126 ± 6, respectively) (13,18,19). Ostruction of the left ventriculr outflow trct (LVOTO) cused y SAM is found in one-third of ptients with HCM t rest (13, 15) nd occurs in up to two thirds of symptomtic ptients which hve no ostruction t rest ut do so during mnoeuvres tht reduce prelod nd fterlod or increse contrctility (20). LVOTO in ptients with HCM is considered cliniclly significnt when grdient greter thn 30 mm Hg t rest or greter thn 50 mm Hg is encountered during mnoeuvres y echocrdiogrphy, such s exercise, Vlslv or phrmcologicl stress (21). Surgicl intervention is recommended in ptients who hve not responded to phrmcologicl mngement. Septl ltion with lcohol is recommended in ptients who re not cndidtes for surgery nd older ptients regrdless of whether or not they re cndidtes for surgicl mngement (6). Trnsthorcic (TT) or trnsesophgel (TE) echocrdiogrphy with Doppler is usully the first test performed when there is suspicion of LVOTO or HCM, for the identifiction nd clssifiction of the severity of suvlvulr stenosis ccording to the pressure grdient. Crdic MRI my provide importnt dditionl informtion to define in detil the ntomy of the LVOT, including the degree of hypertrophy nd the precise loction of the thickening of the myocrdium, evlution of the vlvulr nd suvlvulr mitrl pprtus nd presence of myocrdil firosis tht is mnifested in lte enhncement imges in inversion sequences (22). Crdic MRI cn lso e used to mesure the re of the hole of LVOTO, which is determined y trnsplnr flow plnimetry using phse contrst sequences (figure 1f), which hs demonstrted to e relile prmeter for chrcterizing ptients with ostructive HCM. Contrry to routinely used prmeters on echocrdiogrphy, MRI is free of interoserver vriility, conditions of imge vriility nd is non-invsive method (22-24). Mesurement of the trct re y MRI is useful to define the degree of ostruction. An outflow trct <2.7 cm 2 during systole, with crdic MR, hs sensitivity nd specificity of 100% to differentite ostructive nd non-ostructive form of HCM (25,26). The min role of MRI in ptients with HCM is to clrify the dignosis nd phenotype (6,27-31). In ptients in whom echocrdiogrphy is inconclusive usully through poor coustic window or when hypertrophy is locted in regions tht re not esily visulized y this method, crdic MRI should e performed (6,32). Lte enhncement sequences llow the identifiction of res of myocrdil firosis in ptients with HCM. Ptients with evidence of myocrdil firosis nd CMR hve een ssocited with risk mrkers for sudden deth, mlignnt ventriculr rrhythmis nd electrocrdiogrphic disorders (33-38) Left Ventriculr Outflow Trct Ostruction. Zulug A., Aldn N., Gutiérrez C., Bustmnte S., Muñoz P., Zulug N.

3 review rticle d e c f Figure yer-old ptient with predominntly nteroseptl sl HCM nd ostruction of the LVOT due to hypertrophy of the sl septum nd SAM. CMR, SSFP (stedystte Free precession) sequences in different phses of the crdic cycle, long xis projection of three chmers ( nd ) nd short xis in the Mitrl vlve plne (c nd d) where systolic lood pressure movement (SAM) is oserved oth of the nterior vlve s well s the posterior leflet (rrows in nd d) which determines the contct of the sme with the interventriculr septum. Note the norml loction of the leflets (centrl plne) in the others phses of the crdic cycle ( nd c). Immeditely fter SAM note the ccelertion of flow in the LVOT (rrow on e). Phse contrst sequence in plne perpendiculr to the trct to determine pek speed nd re of the outflow trct in systole (rrow on f). LVOTO y memrnes, diphrgms nd suvlvulr infundiulums They my hve different morphologies; the most frequent form is firoelstic tissue memrne or spine tht extends from the endocrdil surfce of the sl septum nd protrudes to the outflow trct, eing le to extend to the se of the nterior vlve of the Mitrl vlve (Figure 2). Indictions for surgicl tretment of ptients with memrnes, diphrgms or infundiuli of the ventriculr outflow trct depend on the clinicl mnifesttions, the grdient pressure nd morphology of the lesions (1,12). LVOTO in ptients fter closure of ventriculr septl defect (VSD) L ostrucción suvlvulr tmién se h informdo luego del ciesuvlvulr ostruction hs lso een reported fter surgicl closure of ventriculr septl defects nd is elieved to e due to prolifertion of firotic tissue t turulent flow sites (39). The memrnes locted immeditely djcent to the ortic vlve or extending to the nterior Mitrl vlve re more likely to led to progressive ostruction nd ortic vlve injury with insufficiency (Figure 3) (1,40). LVOTO fter Mitrl vlve surgery In ptients undergoing Mitrl vlve replcement, outflow trct ostruction is one of the postopertive complictions (22). Ostruction occurs y high profile protrusion of the prosthetic vlve to the outflow trct or y n norml position of the prosthesis t the suvlvulr level. If the prosthesis is not pro- Rev. Colom. Rdiol. 2017; 28(1): perly oriented, one of the ends cn ostruct the LVOT (figure 4) (41). Sigmoid septum The interventriculr sigmoid septum involves the protrusion of segments of the septum to the outflow trct of the LV nd ppers, usully, in elderly ptients with history of hypertension with lowgrde concentric hypertrophy of the LV myocrdium (thickness of the myocrdium in distole usully etween 12 to 16 mm) (figure 5). The decrese in the ortoseptl ngle Is typicl of ptients with sigmoid septum. Recently It hs een proposed tht the sigmoid configurtion of the septum my led to dynmic ostruction of the LVOT even without ventriculr hypertrophy. In some cses the sigmoid septum my cuse stenosis of the LVOT with dynmic ostruction nd n increse in the pressure of the LV, especilly if there is hypertrophy, physicl exercise, generl nesthesi, cute myocrdil infrction (AMI), dehydrtion or ggressive mngement of hypertension (42,43). Vlve ostruction Aortic vlve stenosis Aortic stenosis is common disese tht usully ffects older ptients. There re two importnt fctors tht mke it one of the most common vlvulopthies:. pproximtely 1-2 % of the popultion is orn with icuspid ortic vlve, which is prone to stenosis nd. ortic stenosis develops with ge. Clcified ortic stenosis ws considered degenertive lesion; However, it shres mny chrcteristics with coronry rtery 4611

4 Revist Colomin de Rdiologí disese. Both re more common in men, older people, ptients with hypercholesterolemi nd oth re derived from chronic inflmmtory process. Aortic stenosis differs from sclerosis due to the degree of vlve involvement. In ortic sclerosis, the vlves re normlly thickened nd the ostruction of the outflow trct is miniml. In contrst, in ortic stenosis the functionl re of the leflets hs diminished sufficiently to cuse mesurle flow ostruction (44). The ivlve ort (Figure 6) occurs y norml vlvulogenesis with the formtion of smll cusp nd lrger cusp, usully y congenitl fusion of one of the vlvulr commissures. This disposition mkes the vlve more susceptile to trum nd finlly leds to clcifiction nd firosis. By the time the ostruction of the outflow trct cuses significnt symptoms, the vlve is rigid, clcified mss tht mkes it difficult to determine the etiology of process. This type of vlve configurtion is usully not ostructive erly. Vlvulr stenosis develops etween the fourth nd sixth decde of life nd represents > 50 % of cses of ortic stenosis disese in people under 70 yers of ge. The presence of ivlve ortic vlve is ssocited with n increse in the incidence of complictions such s stenosis, insufficiency, endocrditis nd neurysml dilttion of the ort (1). In developed countries, ortic stenosis is usully relted to risk fctors similr to those which cuse therosclerosis. Another mjor cuse of ortic stenosis is rheumtic disese, which genertes inflmmtory dhesions of the vlvulr cusps tht led to fusion of the commissures nd, consequently, to vlve stenosis nd/or regurgittion (45,46). As the compromise is greter, ventriculr dysfunction occurs. Initilly, the ptients re symptomtic nd systolic reth cn e found in n incidentl mnner. As the disese progresses, the symptoms it produces re ngin, dyspne, syncope nd, finlly, hert filure. Once the symptoms pper, survivl without surgicl tretment is 2 to 3 yers (45). Doppler ultrsound cn e performed in most ptients, ut the severity of the stenosis my e underestimted if the qulity of the imge is poor nd is ffected y technicl fctors. CT is useful for the quntifiction of vlvulr clcifiction (severe: > 1000 Agtston units) nd in ptients to whom they will prctice trnsctheter replcement, to undergo plnimetry nd tke mesurements of the vlvulr ring re, vlve leflet length nd the distnce from the ring to the coronry ostium; It is lso sought to determine the dimensions of the ortic root, the severity of the vsculr disese nd the stte of the coronry rteries (Figure 7) (47). MRI llows etter chrcteriztion of the myocrdium in ptients with ortic stenosis nd the detection of firosis with lte enhncement sequences. A pttern of ptched nd suendocrdil enhncement hs een descried, which predomintes in sl segments. It hs een shown tht the lte enhncement, s n indictor of myocrdil firosis, is fctor of independent risk of mortlity in ptients with moderte or severe ortic stenosis, nd is ssocited with worse prognosis fter vlvulr replcement (45, 48-50). Figure yer-old femle ptient with memrne in the LVOT. Crdic MRI, SSFP cinem sequences, long xis projection of three chmers () nd phse contrst sequence in the plne of the outflow trct of the left ventricle (), where the memrne is seen extending from the sl septum to the se of the nterior vlve of the Mitrl vlve (rrow in ) which cuses ccelertion of the flow (rrow in ), in systole in the outflow trct. Figure yer-old ptient with multiple crdiovsculr mlformtions, including LVOT memrne, prtil pulmonry venous dringe normlity nd norml ppillry muscles of the left ventricle with septl insertions. Correction of CIV. Crdio CT with reconstruction in long xis three chmers where n olique memrne is oserved in the LVOT (rrows) Left Ventriculr Outflow Trct Ostruction. Zulug A., Aldn N., Gutiérrez C., Bustmnte S., Muñoz P., Zulug N.

5 review rticle Figure yer-old ptient with Mitrl ioprosthesis prtilly ostructing the outflow trct of the left ventricle. Study of crdio CT with long xis of three chmers multi-plnr reconstruction. Protrusion of one of the pillrs of the ioprosthesis ring towrds the outflow trct of the left ventricle (rrow) with ltertion of ortic ngle, which fvors this phenomenon. Figure 5. Aortoseptl ngle in ptient with sigmoid septum. CMRI, SSFP (stedy-stte free precession) long xis projection of three chmers cinem sequence. Bsl septum protrusion (rrow) to the outflow trct in ptient with chronic hypertension, with ortoseptl ngle nd discreet concentric hypertrophy of the myocrdium. Figure 6. Crdic CT in ptient with ivlve ort without stenosis. 3D reconstruction in systole ) nd distole ). c d Figure yer-old ptient with severe ortic vlve stenosis. Ptient in protocol for TAVI plnning, crdio-triggered CT, ) orthogonl multiplnr reconstructions of the ortic vlve in systole nd ) of the vlve ring, c) three-dimensionl reconstruction with superior sight of the ortic vlve in distole, d) multi-plnr reconstruction long xis of three chmers. Antomiclly trivlent ortic vlve ptient, ut with complete fusion of the right nd left vlves, which cuses the vlve to ehve physiologiclly s ivlve with semilunr opening in systole (). A vlvulr re in systole is identified y plnimetry of 0.9 cm2 tht correltes with severe stenosis. The extent of ortic vlve clcifiction is identified through the outflow trct to the se of the nterior vlve of the Mitrl vlve, finding tht must e reported since it significntly increses the risk of perfortion in TAVI procedures (d). Figure 8. 2 yer old ptient with Willims-Beuren syndrome with suprvlvulr ortic stenosis. study of triggered crdio CT, sgittl reconstruction of the ort nd its root where ortic scending stenosis from the sinotuulr junction to the origin of the rchiocephlic trunk with decresed concentric vsculr lumen is identified. The severity of ortic vlve stenosis is clssified ccording to the following prmeters (48): Vlve re (cm 2 ) (mts / sec) Estimted grdient (mm Hg) Low Moderte Severe 1,6-2,0 2,0-2, ,0-2,5 3,0-3, < 1,0 > 4,0 > 64 Rev. Colom. Rdiol. 2017; 28(1):

6 Revist Colomin de Rdiologí Suprvlvulr ostruction Aortic suprvlvulr lesions re the rrest cuse of LVOTO. They re chrcterized y diffuse or focl stenosis tht initites t the sinotuulr junction nd occsionlly extends throughout the scending ort. It rrely involves the ortic rch. Aortic suprvlvulr stenosis is often ssocited with Willims- Beuren syndrome (Figure 8). This is n utosoml condition which occurs in 1 in live irths nd in which 71 % of the time there is suprvlvulr ortic stenosis; It is lso ccompnied y mentl retrdtion, stenosis of the pulmonry rteries, prolpse nd up to 50 % of ptients present ortic vlve normlities, minly ort ivlve. This syndrome cn e ccompnied y ltertion in the perfusion secondry to some degree of ortic vlve dhesion in the sinotuulr junction tht restricts the distolic filling of the coronry rteries (1). Stenosis of the sinotuulr region cn e surgiclly extended when the ptient hs symptoms such s ngin, dyspne nd syncope or when there is n verge pressure grdient greter thn 50 mm Hg (1). Conclusion Currently, crdic mgnetic resonnce plys leding role in the evlution of ptients with ostruction of the left ventricle, especilly in the ssessment of hypertrophic crdiomyopthies nd in ptients where echocrdiogrphy is unfinished or techniclly limited. The detection of myocrdil firosis using lte enhncement llows detecting those ptients who re t incresed risk of sudden deth, mlignnt rrhythmis nd electrocrdiogrphic disorders. References 1. Aoulhosn J, Child JS. Left ventriculr outflow ostruction: suortic stenosis, icuspid ortic vlve, suprvlvr ortic stenosis, nd corcttion of the ort. Circultion. 2006;114: Fttl J, Henry MA, Ou S, Brdette S, Pps K, Mrcotte F, et l. Mgnetic resonnce imging of hypertrophic crdiomyopthy: eyondleft ventriculr wll thickness. 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