Aortic Stenosis (M/A)

Aortic Stenosis (MA48)

-Classify by Valvar, Subvalvar, Supravalvar

VALVAR AORTIC STENOSIS

Epi

-Bicuspid Ao valve and other minor malformations are common and often unapparent as a kid

-Bicuspid Ao valve occurs in 1.3% of people

-AS is 3-8% of CHD seen in infants (and 0.8% of infants have CHD)

-Only 2% of pt w a congenitally AbNl Ao Vlv will have signif stenosis or regurge by teens, though a high percent will have progressive vlv dysfx later on and need surgery by adult life

-60-75% of congen AS is valvar. M>F (3-5:1).

-Assoc xx- VSD, CoAo, PDA

-Valvar AS incr risk w Turner synd, Jacobsen synd; some genetic basis for it...

Path

-Ao vlv dvp fr 3 swellings (ridges) of subendocardial tissue formed when the Ao-Pulm septum divides the bulbus cordis and truncus arteriosus. Each ridge undergoes cavitation (hollowing) to form thin, smooth, pliable leaflets and the sinus of valsalva.

-Nl valve has 3 pocketlike cusps, equal in size, with Nodules of Arantii- a fibrous nodule at center of the free edges of each semilunar cusp, that meet in the center of when the valve closes.

-The valve is surrounded by a fibrous ring where the cusps attach

-Stenosis occurs w decreased orifice size fr thickened and increased rigidity of valve leaflets

-Bicuspid Ao Valve (#1 cause)- only 2 cusps bc partial/complete fusion of 2 of the Ao valve cusps, +/- central fibrous bridge (raphe) at the fusion site

-Very variable- how conjoined are they, cusp size/equality, central or eccentric orifice

-75%- R&L cusps are conjoined; rest are mostly R+noncoronary cusp

-Unicuspid valve- >1cusp is fused--> slit like orifice only

-All 3 cusps fused w only a small orifice

-No cusp fusion but hypoplastic annulus--> AS

-Myxoid dysplasia of a tricuspid nonfused valve- uncommon

-Calcification, fibrosis, lipid accum'n, inflmy changes, myxomatous degen'n, annular dilat'n, acquired fibrotic fusion of true commissures all can cause AS

-Ca'ion- rare in kids/teens, but ~ universal in old ppl w Ao vlv AS

-Fibrosis & Lipidosis incr w time--> thick stiff cusp w AS

-Fibrosis at the fusion site--> impaired valve opening

-Some pt w valve xx--> cystic medial necrosis--> weakened Asc Ao--> annular dilation and dilation/aneurysm of Asc Ao--> incr risk dissection/rupture, independent of the degree of AS. Annular dil'n assoc w AR. ?etiology of the dilation, but Fibrillin1 content in the wall is reduced, and metaloproteinase2 activity increased.

-AS--> Pressure OD--> LVH and myocardial fibrosis seen w AS; can --> much endomyocardial fibroelastosis and pap muscle infarct in infant w sev AS. Can also occur in ASx child w moderate congen AS.

Physiology

-LVOT obstruction--> inc LV AL.

-Nl pt: SBP @LV = SBP @Asc Ao

-AS: LV SBP > Asc Ao SBP w ejection bc decr effective area of Ao vlv orifice

-If Nl SV, then manitude of the P gradient reflects severity of AS

-LVH to compensate for incr AL (see law of LaPlace) --> maint Nl LV wall stress despite incr pk sys P

-SV, CO, baseline HR, EF all remain Nl (usually), though contractility is decr, and LVED Vol and Pressure is incr if severe symptomatic AS

-LV subendocardial ischemia and infarct can occur, even if coronaries are unobstructed, bc myocardial demand of the hypertrophied LV is increased, and cor Q isn't enough.

-Assess w Diastolic Pressure Time Index (DPTI)= (mean diastolic grad bn LV and Ao) x (diastolic length) = area bn Ao and LV pressure curves during diastole = ~O2 supply; Myocardial

O2demand can be estimated by Systolic Pressure Time Index (SPTI)= area under LV P curve during systole.

-Ratio of DPTI:SPTI can be sued to quantify O2 supply/demand ratio of LV

-Mean Sys P grad- calculated from the doppler, correlates well w the mean P grad from cath

-States of incr SV or Contractility --> higher P gradient.

-Pt w very sev obst can --> AbNl'ly low myocardial systolic fx--> low CO--> low P gradient

-so many want to use valve area calculations rather than P grad to gauge severity of obst

-Ao Valve Area- Continuity Equation- vol of Q per cardiac cylcle is teh same as Ao valve as at the mitral valve or in LVOT. So: Ao vlv area (cm2) = (LVOT area)(mean LVOT velocity)/(mean Ao vlv orifice velocity).

-Nl Ao vlv in teen/adult is 3-4cm2

-mild >1.5cm, mod 1-1.5cm2, sev <1cm2

-Kids- Nl 2cm2/m2, mild >0.75, sev <0.5

-TDI- check for sys and diast dysfx

-Sx in pt w Nl EF has been attributed to dias dysfx- assoc w incr filling P, incr myocardial stiffness

-Doppler fr mitral or pulm vn to estimate LV filling P- d/o loading conditions, HR, other factors that limit usefulness.

-TDI for sys/diast mitral annular velocity- allows quantification of sys long axis fx and diast fx

-E:E' (E=early mitral inflow v, E'= early diast mitral annular velocity) E:E' correlates to LVEDP, so good to check diast dysfx. TDI for sys fx on long axis can check for dysfx even if Nl EF. Longitudinal fibers are in the subendocardium, so more vulnerable to ischemia than circumferential fibers. Thus Long axis dysfx might precede transverse axis dysfx.

Cardiac MRI:

-check LV mass & fx

-able to check P grad and Ao vlv area quantification, correlates well w Doppler

Cath:

-Gold standard, but often no longer needed. Usually only for Tx w balloon valvuloplasty

-Check CO w Fick/TD, LVEDP, P grad (mean and pk to pk); angio for LV size/fx, Ao vlv annulus size, degree of leaflet thickening & cusp mobility, cor art patency, Asc Ao contour/size

-Gorlin Method- calc effective valve orifice area- (Ao vlv Flow)/(44.3 x sq root of mean P grad across the vlv)

-AVF determined fr CO and sys ejec pd- check SET (sys ej time) = check simultaneous P tracing from Ao to LV. Sys Ej Pd (SEP) per min (S/min) is determined by SET xHR. (SEP= SET xHR)

-AVF (mL/s) = CO/SEP

-Mean P grad (mmHg) - determined fr planimetry using simultaneous P tracing fr Ao & LV

-Ao Vlv Area is then calc fr: AVF/(sq root of MPGx44.3)

-Ao vlv orifice area reps the most reliable index of stenosis severity (in theory), bc unlike P grad, it doesn't depend on loading conditions and HR

NHx:

-f/u data is poor, so hard to know, esp w such wide Sx range...

-if present as infant, likely more signif AS, w higher mortality (even w Tx)

-25% of pts in one study were <2yo and the 1yr survival was 64% in these pt, despite surg for most

-if >2yo at study enrollment, the 25yr survival was 85%

-Mild AS can be stable for years, but eventually progresses

-1%/yr get bacterial endocarditis in some series, but likely lower (0.27%) in another study. incr AS--> Incr risk.

Tx:

-SBE ppx

-exercise restrictions (36th Bethesda Conference guidelines)

-Nearly all progress and pt will need surgery, (unlike in adults where we limit intervention. Goal survival in kids is>50yrs, while in adults a 20yr survival is c/s long term.

-Balloon valvuloplasty is usually done before any surgical valvotomy, and with either procedure valve replacement is eventually needed for subsequent AS/AR.

-Adults w congen Ao vlv stenosis will get cusp Ca'ion--> poor results w valvotomy/plasty so usually replace valve as young adult

-Kids/Teens w AS and signif AR will need replacement of the valve

-ACC/AHA-->

ASx:

Intervention based on Doppker pk to pk instantaneous gradient

>70mmHg c/s for all pts

50-70mmHg and competitive sports/future pregnancy

Intervention based on Cath pk to pk instantaneous gradient

>60mmHg c/s for all pts

>50mmHg if competitive sports/pregnancy

+Sx (angina, syncope, DOE), ischemia, repol'n changes on ECG

-valvuloplasty if >50mmHg grad

-c/s alt cause of Sx/Si if <50mmHg

-No valvuloplasty if <50mmHg and ASx unless CO is decr

-If milder AS, check ECG and echo Doppler

-If pk Doppler grad ?36mmHg (pk v >3m/s), then f/u q 1yr

-If pk <36mmHg, then f/u q2 years

-If pk >36, then c/s ECG if pt interested in sports

-c/s cath if ECG and echo are discordant w each other (to check pk to pk grad)

-36th Bethesda Conf Task Force Sports recs:

-Mild AS = cath pk to pk <30mmHg, mean Doppler grad <25, or pk instant. Doppler grad <40 ==> cleared for all competitive sports if ASx and Nl exercise tolerance

-Mod AS- cath pk to pk 30-50mmHg, mean Doppler grad 25-40, pk Doppler grad 40-70mmHg ==> if ASx, AND mild-no LVH, and no repol'n xx on ECG, and Nl exercise test. ==> ok for sports with low static compenent and low-mod dynamic component (e.g. golf, bowling, baseball, volleyball)

-If no SVT/VT ==> ok for mod static component and low dynamic comp (diving, archery, motorcycle, archery)

-Sev AS = cath pk to pk >50mmHg, mean Doppler grad >40mmHg, pk Doppler grad >70mmHg ==> no competitive sports

-If Bicuspid Ao valve, but no AS/AR, they are still at risk for progressive Ao root dilation/dissection, and mortality risk is same in younger pt than pt >40yo!!

-Ao Dissection- 9x incr risk if bicuspid vlv (thus more common cause of dissection than Marfan bc bicuspid vlv is common).

-Nearly 1/2 of teens/20s w bicuspid vlv have Ao root dilation

-Most pt w dissection have htn, so must manage the BP well.

-B-blocker/ACI not proven to help in normotensive pt, but are good for pt w htn

-Ao dilation is precursor to dissection so monitor closely if +dilation; c/s prophylactic surgery even if ASx if Ao diam is 5cm or more, or if rapid Ao growth rate (out of proportion to body)

Aortic Valve Replacement

-if progressive AR or recurrent AS despite balloon, then c/s surgery or replacement (surgical repair isn't very durable)

-Mechanical Valve- most durable, but must anticoagulate and it can't grow, so ng in small kids

-Bioprosthetic Valve- homograft- no anticoagulation needed, but still can't grow, and poor longevity, espec. in small kids.

-Ross procedure- used in some centers for kids/infants- Pulm valve used for Ao, and homograft for new pulm vlv; here Ao vlv (old pulm vlv) can grow. But, here there can be pulm homograft dysfx in most patients even soon postop. And many can have dysfx of neoaortic valve.

-PerQ Ao valve replacement- new, for adults, espec if sev AS and inoperable.

Valvar AS in Infancy

Sx:

-10% of AS presents as infant w CHF Sx

-in utero, mild-mod AS--> inc LV P +/- LVH; sev AS--> signif LVH w decr LV compliance--> decr Q thru L hrt--> LV/MV/Ao vlv annulus/LVOT hypoplasia; +/- CoAo +/- Asc Ao hyoplasia

-Endomyocardial fibroelastosis +/- papillary muscle infarction bc of VO2/DO2 mismatch

-Thus Sev fetal AS can --> HLHS

-bc RV can handle entire CO, the fetus can handle sev AS well even w LV hyoplasia, but once born, Sx dvp quickly

-ASx till PDA closes if LV is big enough/good enough Fx, then decr PO, tachypnea, FTT, sys Murmur +/- gallop, hepatomegaly, weak periph pulses

-If sev AS, LV cant handle a full CO so when PDA closes, --> shock, hyperdynamic RV impulse, tachypnea/retractions, but not always a sys murmur!!

Eval:

-Echo- check fx, Ao size, increased echodensity of enodmyocardium/mitral valve pap muscle = fibroelastosis/pap infarct; RV enlargementl check fr CoAo, cor tratriatum, supraannular Mitral stenosis, pulm vn stenosis, Asc Ao hypoplasia/dilation

-NOTE that Ao vlv grad may be less than actual stenosis bc of decr CO due to poor fx

Tx:

-PGE right away, +/- inotropy for fx, avoid supp O2 if ductal dependent, avoid hypervent'n if intubated

-Critical AS + small LV- check if LV is good enough to support a 2 ventricle repair

-non-apex forming LV, small Ao annulus (<5mm), small MV annulus (<9mm)- maybe better survival with Norwood palliation or transplant then with 2 ventricle repair (MA48 ref 105)

-Rhodes (MA48 ref 106) predictive success equation for 2ventric repair: Ao dimension indexed to BSA, ratio of long axis of LV to long axis of heart, and indexed mitral valve area

-Congen Heart Surgeons Society prospective multicenter study (MA48 ref 107) for 5 yr survival--> d/o age, Ao vlv Z score, gr of endomyocardial fibroelastosis, Asc Ao diam, signif TR, and LV length Z score

-signif retrograde Q thru distal Ao arch via PDA is assoc w lower success in 2vent repair

-If 2vent repair==> balloon valvuloplasty/surg valvotomy soon (both good but balloon may --> higher degree of AR & surg valvotomy incr risk residual/recurrent stenosis).

-Mechanical valve ng bc of poor tissue durability

-Ross-Konno preferred- Ross = pulm vlv autograft; Konno = dilate Ao annulus

-Resecting endomyocard fibroelastosis might incr growth potential in borderline LV

-Some c/s Norwood with subsequent Rastelli for a 2 vent repair (!)

SUBVALVAR AORTIC STENOSIS

Epi:

-10-20% of AS in kids; M>F 2-3:1, 1/2 w assoc CHD- VSD, CoAo, AVCD, valv AS, MV xx

-Rare in infants (except for malalignment VSD w post dev of outlet septum into LVOT)

-likely acquired bc not often seen neonatally, due to abNl endothelial substrate that undergoes abNl prolif due to ? stimulus- abNl shear stress fr abNl Q pattern fr geometric/anatomic LVOT variation- incr mitral-Ao separation/steeper Aortoseptal angle. ?tissue causing it- maybe embryonal endocardial cushion tissue

Path:

-collar or ridge of membranous &/or fibromuscular tissue encircling the LVOT, or is diffuse/tunnel like.

-may have a membranous curtain arising fr a muscular base

-made of collagen fibers, elastic fibers, myocytes; fibrous tissue may be tethered to Ao vlv or ant mitral leaflet.

-Mitral valve xx- insertion of pap muscle or chordal tissue into septum/Ao leaflet, accessory mitral valve tissue, muscularization of sub Ao part of ant leaflet.

-Ao vlv- maybe thick, usually tricuspid. Ao vlv abNly are usually acquired, maybe bc of turbulent flow jet damaging the Ao valve cusps; but might be bc of an underlying dz substrate

Physiology:

-fixed subAo stenosis- similar physio to valvar AS, w P OD to LV--> LVH; LVH usually proportional to AS but can be out of proportion too. xx of subendocard ischemia/fibrosis too...

Sx/Dx:

-Dx w echo

-if isolated, usually p/w ASx murmur- first thought to be innocent, but then progresses so it sounds like an LVOTO. CP/Syncope only if sev AS.

-SEM loudest at L mid sternal border w rad to USB and suprasternal notch

-DDx subvalvar AS bc no systolic click

-LV impulse may be hyperdynamic,

-May have AR or MR

-ECG: LVH often, even if mild AS, but can be Nl in sev subAo stenosis

-CXR: usually Nl, Asc Ao dilation uncommon

-Echo: high Sn/Sp. May see early systolic partial closure and fluttering of Ao leaflets. check Ao/mitral anatomy & fx closely.

-Doppler --> v accel of pk instantaneous and mean P grad.

-Coexistant Ao vlv stenosis- see w additional PW doppler velocity that increases above Ao vlv

-TEE if you need to better see the LVOT anatomy

-Cath: not needed usually