Hypoplastic Left Heart Syndrome (M/A)

Hypoplastic Left Heart Syndrome (MA50)

EPI:

-1.4-3.8% of CHD, (0.016-0.036% of all live births), but --> 23% of cardiac death @ <1 week old, and 15% cardiac deat @ <1mo. M>F (55-67% M).

-Family recurrence risk is 0.5-2% if one child is affected, and familial risk for other CHD is 2.2-13.5%

-12% prevalence of LVOT xx in 1st degree relatives in some studies, so prob some auto rec inheritance to some degree

GENETICS:

-Extracardiac xx/genetic syndromes in 15-30% -

-Genetics: Turner, Noonan, Smith-Lemli-Opitz, Holt Oram, Ellis-van Creveld synd, Oral-Digital-Facial synd, CHARGE; tri 13, 18, 21, duplic 12p, 2q-, balanced 3:7 translocation, 4q-, 4p-, 7q-, duplication of 16q and 18p-

-Extracardiac xx- CDH, duod atresia, biliary atresia, malro, omphalocele, CF

-NOTCH1 signaling/transcription regulator - mutations have caused Ao dvp xx in mice

-dHAND gene, HRT1 and HRT2 genes are involved in downstream NOTCH signaling, and assoc w familial HLHS

-?link bn maternal Group A Strep ?Ab rxn

-link w maternal exposure to PCBs

FETUS: ECHO & INTERVENTION:

-1989 first noted HLHS in fetus w initial critical AS

-likely dynamic/progression of HLHS thru gestation, bc of a bad LVOT or change in LV inflow (AS; MS/Foramen ovale restriction/atrial septal anatomical problem)

-Balloon dilatin of Ao valve as fetus has had recent success...

Fetal Echo:

-see small, muscle bound LV

-now must decide if this will progress to HLHS

-and must determine if the atrial septum is intact/restrictive bc the pt may do well w prenatal intervention

-Prenatal indicies correlating w HLHS at birth:

-smaller MV & Asc Ao @3rd Tri

-decr rate of growth for all L Hrt structures

-reversal of Q thru FO

-retrograde ductal supply of distal Ao Arch

---(very important for Dx...)

-R/F for HLHS in pt w prenatal AS: mod LV dysfx, retrograde transverse Ao arch Q, L to R atrial shunting, monophasic mitral inflow (fr diast dysx) on initial prenatal echo

-Having highly restrictive ASD/intact atrial septum increases overall HLHS mortality later on. --> very cyanotic at birth, often Rx unresponsive. Even after quick decompression of the atrial septum, M&M is higher (?bc of 2y anatomic changes to lungs)

-arterialization of pulm veins, lymphatic dilation (?)

-associated pulm art hypoplasia (?)

Fetal Intervention:

-goal to Tx pt w sev LVOTO is to enable future biventricular circ at birth

-risk/benefit is unknown, so intervention not universally accepted; some only do it if critical AS w fetal hydrops

-2000- Kohl reports world experience with fetal Ao balloon valvuloplasty (n=12)- poor outcome, only 1 survived "long term"

-2005- Lock- better outcome- 27/34 pt had success; xx = fetal death, death bc of prematurity, brady, pericard effusion; maternal xx is rare, but it required laparotomy in 1/2 moms.

-22 were born, of which 6 had bivent circ and 16 had HLHS, but much more were bivent p 2003

ANATOMY:

-HLHS has varied LV hypoplasia.

Underdevelopment of LVOT-Ao Complex

- --> critical Ao vlv stenosis or Ao vlv atresia with intact ventric septum

-spectrum: Ao vlv atresia w mitral atresia, Ao vlv atresia w patent mitral vlv, AS w patent mitral valv (~ to just plain critical AS)

-The underlying issue is that the growth/dvp of vasc structures d/o (in part) the amt of Q during dvp

-Asc Ao is hypoplastic (mean diam 3.3 +/- 1.7mm, with 1/2 had Asc Ao <2mm)

-Asc Ao is only a conduit for retroQ to coronaries

-80% have CoAo

-AS+MS = ~1/4 of HLHS that get Norwood; AA+MA (atresia) = 36-46% of HLHS that get Norwood, and 20-29% are AA+patent Mitral vlv

-R heart also changes- larger structuresL RA, tri vlv, PA, pulm vlv. RV enlarged and RVH

-RV folds around the LV so it will make up the apex of hrt. This can affect tri vlv anatomy and RV fx

-up to 35% HLHS have tri vlv xx

-AA w patent MV--> LV inflow only so much LVH (>Nl mass), and of course bigger than AA+MA. This larger LV mass can distort RV inflow portion.

-SEptal surface of RV might have deep apical sinuses/recesses bc the apex of RV has folded around the hypoplastic/hypertrophic LV. Tricusp subvalvar area more distorted than AA+MA, and 1/2 have tri vlv dysplasia.

-Bileaflet R AV vlv are seen in 12% of pts, and 1/3 have tri vlv dysplasia to some degree

-RV vol overload w annular dilation can also cause TR.

-RV subendocardial ischemia as neonate (a or p Norwood) can also --> TR; see bright papillary muscles on echo c/w ischemia, and elongated cords in assoc w TR.

-Ao Atresia and patent MV may increase mortality. Endocardial fibroelastosis common, and can --> subendocard ischemia bc of suprasyst LV P. Also the TR and incr risk of arrhythmia fr endocard fibroelast can --> incr risk.

-AS + patent MV have least Sx. Likely dvp later during fetal dvp when LV is more formed already.

-On spectrum w a critical AS

-Hard to pick 1 vs 2 ventric repair- usually Norwood if LV doesnt form apex and mitral vlv is hyoplastic

HLHS w +VSD

-can be similar to w/o VSD (espec if small VSD), or very different- forms of DORV- e.g. DORV w mitral atresia w/o obstruction of Ao outflow; & (some) unbal Ao endocard cushion defects (bc some have hypoplastic L heart)

Other Anatomic Considerations

-L SVC in <5%; AbNl pulm vn connection in 5%

-often see levocardinal vein draining to inomm vn (it's decompressing the hypertense LA...)

-coronary abNlies are rare, though cor fr RPA has been described; even though Ao is small, coronary ostia are Nl...

SX, DX, ECHO:

Sx:

-usually dx via OB US, then planned delivery at 3y hospital, usually vaginal

-PGE postnatally for PDA, then echo to check Dx

-Have cath dr on hand in case need to make larger ASD

-Without prenatal dx, presentation can vary and d/o amt of atrial level shunting. As PVR decr, 1/4 of pt will present within 24 hrs, bt most get Sx p 48hrs of life. Restrictive ASD--> LA htn and pulm congestion, so present sooner, while larger ASD presents later as PDA close--> shock or tachypnea/feeding difficulty at 2-3 days of life

Dx:

PE:

-Sev restrictive ASD: intense cyanosis/resp distress

-Non restrictive ASD: more pink,

-As PDA closes--> more lethargic, resp distress, cool limbs, pale

-benign ausc exam, but S2 can be single, loud- bc no A2 and +Pulm htn

-+/- S3 espec if ventric dysfx

-no murmur usually, but can get soft SEM bc incr Q accross pulm vlv

-if TR, may hear a louder S1 coincident murmur

-pulses are palpable and symmetric initially, and then reduce w PDA closing

-+hepatomeg if delayed presentation

CXR:

-not Dx, but d/o degr of ASD restriction- if sev--> Nl hrt size but signif pulm edema (thus confuse w lung dz). If nonrestrict ASD--> pulm overcirc w cardiomegaly- prominent R atrial border w no Asc Ao shadow.

ECG:

-nondiagnostic. --> RAD and RVH (but hard to ddx Nl newborn ECG). Tall, pkd p wave = RAE in 1/3

Echo:

-PSLA

-small, muscle bound LV that doesn't extend to the apex

-echobright endocardial surface = endocard fibroelastosis

-LA small, but can be dilated if restricted ASD

-Asc Ao is samll (2-3mm diam), +/- patent Ao vlv

-MV often imperf, but if patent, leaflets are thick, short/absent pap chordal attachments

-VSD rare if AA. Color doppler of IVS may show ventriculocoronary art connections

-DDx critical AS- HLHS has LV cross sctl area <1.5cm2, LVED inflow <25mm (fr hingepoint of post mitral leaflet to the apex) & a mitral annulus diam of <6mm.

-PSSA

-Check LV size/fx

-Check Mitral valve pap muscles

-Check Ao vlv size and anatomy

-Check Doppler of cor art- bidrectional cor Q = LV-cor art connection

-Check MPA, PV, branch pulm arts

-Check PDA entering Desc Ao

AP4C

-Check LV size/fx

-if Apex is largely made fr RV, it's unlikely LV can support syst circ

-Check entire muscular apparatus, including subvalvar/supravalvar areas

-Check Mitral valve anatomy and annulus

-Check RV fx, tricuspid valve anatomy/TR

-Check RV sys fx- can be depressed esp if PDA closes/acidosis

-Tri vlv xx- bileaflet vlv, dysplasia/prolapse, abNl pap muscle

Subcostal

-Best view for atrial septum

-Check for AS aneurysm billowing into RA

-Check for unusual attachments of septum primum- attaches to post-sup LA wall

-Check for small ASD (restrictive)- w pk, mean Doppler grad

-Check pulm vn anatomy/drainage

-check attachment, drainage (=end pt of pulm vn Q)- to LA? esp if intact AS there can be a levoatrial cardinal vein that originates fr LA and drains some/all of the pulm vns, or may have confluence behind LA and then go somewhere else...

Suprasternal

-Check Ao Arch & Desc Ao

-Check CoAo, interrupted Ao Arch

-Check for retrodgrade Q thru arch during systole fr the PDA = ductal dependent syst circ, = LV isn't good enough for a biventric repair

-Check prox PA and PDA- PDA may be restrictive in a pt presenting late

-Check P grad bn PA and Ao, and recheck p starting PGE

-Check Pulm venous drainage...

-Check L SVC and levoatrial cardinal vein

STAGED PALLIATION:

-1) reconstruct AoArch into the RV outflow, separate branch PA fr RV, create a restrictive source of Qp fr a systemic art or fr the single ventricle.

-2) Unload the single ventricle by replacing the syst-to-pulm shunt with a Superior Cavopulm Anast

-3) Modified Fontan connection fr IVC to PA

-Most Mortality is during and p Stage 1 (5-30% early/interstage mortality), but improved w early Dx, preop stabilization, early repair, syst mgt approaches, and incr monitoring at hm...

Parallel Circulation

-Parallel circ before, during, and after stage 1

-ensure enough O2 delivery for good outcome...

Cardiovascular Reflexes & Physiology of Shock

**see the newest MA text for better physiology discussion**

-Global C.O. d/o PL, AL, HR, rhythm, Contractility, and AP shunts

-Regional resistance d/o interaction bn neurohumoral factors related to inflm, symp n sys, and local autoregulation factors. Total SVR d/o net effect of regional resistances.

- DO2= Qs*CaO2; CaO2 = O2 content = 1.34*Hgb*SaO2+PaO2*0.003

-Shock--> Prioritize Q to brain/heart, at risk of ischemia to mesenteric/splanch circ; inc reflexes to hemorrhage/hypOtension w incr baroR' gain to incr contractility, HR, SVR, decr venous capacitance.

-This would help w hemorrhage, but actualy impairs Qs if pt has myocardial dysfx

-This response is also triggered by stress, pain, anxiety.

-It's strong enough to incr BP despite low CO; thus pt has low CO and high SVR

-Splanc circ organs are first to get ischemia bc of rich symp stim here and bc selective effect of angiotensin

Oxygen Flux in Single Ventricle Parallel Circulation

-DO2 is reduced because SaO2 is reduced due to mixing of oxy and deoxygenated blood, and bc of reduced Qs.

-Fick: VO2 = Qs(SaO2-SvO2) ; VO2 = Qp(SpvO2-SaO2) ==> Qp/Qs = (SaO2-SvO2)/(SpvO2-SaO2)

-Best DO2 is w lowest CO when Qp=Qs. This means total CO (Qt) is 2x Nl CO of each ventric, so that both Qp and Qs are normal....

Monitoring the Parallel Circulation

-follow SaO2, espec central venous sats, with AV diff goal 25%. If Qp=Qs, then expect SaO2 75%, but Sats alone are NOT reliable bc of other facters (VO2, CO, etc). A wide range of tissue/central venous sats can occur at a given SaO2, and DO2 can be impaired even w SaO2 of 75-80%

-In past, thought that increasing FiCO2 would help incr PVR to balance Qp/Qs, but this doesn't work..., same with sub atm FiO2.

-Having a fixed shunt for Qp (BTS/Sano/Brawn) gives a fixed resistor similar to SVR, so changing PVR isn't as efficacious. And, reducing FiO2 <30% may prevent full oxygenation of the blood thru lungs, so SaO2 may come down but not bc of a reduction in Qp.

-Unless you have enough FiO2 to fully saturate blood in lungs w O2, and you have a measure of SvO2, relying on SaO2 to calculate Qp/Qs isn't reliable- may be falsely low bc of variability in AV sat diff and SpvO2 (pulm vein sat)

-Because SVR & PVR are so important in Qp/Qs, the shunt size is critical.

-Low CO + high Qp/Qs can significantly impair DO2

-Even w BTS/Sano, controlling a high SVR is more efficacious than incr PVR.

-Periop mgt based on SaO2 has an early mortality of >20% (so don't rely on it!) - from a sudden acute HD event un an otherwise stable pt postop.

-Symp vasomotor tone/SVR incr w decr Qs, so changes in Qp/Qs occur quickly--> dcr DO2, but not apparent w BP or SaO2 immediately.

-You cant get a true mixed venous sat w HLHS, but can get SVC sat for somewhat mixed venous sat

-Using SvO2 "has greatly reduced periop occurrence of sudden unexpected circ collapse"

-

-NIRS (near infrared spectroscopy)- measure avg oxyHgb sat (rSO2) 2-3cm below skin, usually at forehead, but also at T20-L2 flank for somatic sats. Using 2 NIRS (cerebral/somatic) allows both regiona and global VO2 asssessment

Preoperative Preparation:

PGE1

-20% of kids have fx'l duct closure by DOL1, and >80% by DOL2, so start PGE1 stat.

-If pt in shock fr closing DA, start at 0.05-0.1mcg/kg/min, then decr to 0.01mcg/kg/min

-use lowest PGE dose possible. xx = hypotension, resp depression

-Caffeine (20mg/kg load, 5-10mg/kg/day maint) has helped reduce mech vent need pre-op

Resp Support & Inspired Gases

-PPV (but avoid hypervent) can limit Qp, PEEP allow lung vol >FRC --> compress pulm vasc--> Incr PVR

-Medical gas to incr PVR: CO2 was used in 1990s- lowers pH--> raise PVR, incr Qs in animals; sub atm FiO2 also does the same in animals, - use blended N in gas... (****NOT USED at TCH, clinical: no longer seems effective enough to justify not going to OR)

-Neuromusc blockade can decr VO2

-Studies: yes they may decr SaO2 and Qp/Qs, but only incr CO2 improved DO2, and while it did improve cerebral oxygenation, hypoxia (subatm FiO2) did NOT help w cerebral sats.

-Avoid supplemental FiO2 bc --> vasodilate--> Decr PVR, unless lung pathology...

-If restrictive ASD--> may need supp O2, but really likely needs balloon atrial septostomy

Vasoactive Meds

-If +shock, or decr RV fx may benefit fr inotropy.

-Inotropes have been shown to decr or have no effect on Qp/Qs

-If high Qp/Qs, try milrinone (PDE inhib), but it also decreases PVR, so may incr Qp/Qs, and could cause signif hypotension if pt already at risk for low Qs bc of an AP runoff

Other Tx

-Keep Hct >50% for better DO2

-Keep SVR low enough - low ds morphine if agitated/decr WOB, MA--> avoid feeding bc of variable SVR, decreasing PVR, and potential for syst hypO Q; and give TPN w 10-20% MORE volume than Nl neonate to acct for capillary leak (!).

-Diuretics only if resp distress fr interstitial lung edema bc of pulm overcirc

Surgical Management

STAGE 1 Palliation

-Goals:

-Relieve ductal dependent systemic flow

-Provide unrestrictive coronary Q

-Create nonrestrictive ASD to prevent pulm vn htn

-Provide reliable but restricted source of Qp

-Approaches:

-Modified Blalock-Thomas-Taussig shunt

-Usually originates fr Inomm Art or Ao

-Qp d/o length & diam of the shunt, in large part

-Q to Ao/coronaries is impaired by diastolic runoff to lungs via BTS, and Qp/Qs mismatch

-Competition bn cerebral & pulm is possible if BTS is fr Inomm Art

- xx- occlusion fr thrombosis/thromboembolism

-RV to PA conduit (Sano modification)

-Conduit directly fr RV so Qp only w systole, like Qs--> no aortopulm runoff during diast--> better cor and syst perfusion P, less ventric ischemia (?).

-Unknown what long term impact of ventriculotomy will be. Also no identified diff in outcome...

-Hybrid

-Surgical branch PA band + transcath PDA stent, and create unrestrict ASD --> no need for CPB/deep hypothermia

-Connect Asc Ao and pulm root to provide Qcoronary,

-Mortality bn Stage I and II is in part bc of insuffic Qcoronary, so ensuring enough Q to Ao is important

-Arch reconstruction, eg coarctectomy, may reduce later arch obstruction

-Branch PA banding is reported as a succesful approach to reduce too much Qp to allow a later Stage I repair or reduce mortality till getting a transplant.

Anesthesia for Stage I Palliation

-Anesthesia mgt can reduce mortality fr trauma/surgical stress w subsequent neurohormonal/cytokine release.

-Improved outcome w use of: opioids that decr stress response, preserve cardiac researve

-20-60mcg/kg Fentanyl before CPB, then cont 10mcg/kg/hr Fent

-Can add low dose volatile anesthestic or benzos as well

-+/- DA 2-5mcg/kg/min or Epi 0.02-0.05mcg/kg/min to counter bal symp reduction...

Afterload Reduction

-Mgt of Qp/Qs via managing PVR guided by SaO2 as an indicator of Qp/Qs, does NOT eliminate early HD collapse, and you haven't dealt w the autonomic influences on SVR

-Instead, choose to deal w SVR- alpha blockers incr DO2 and survival, e.g. phenoxybenzamine--> lowe and less varied SVR. MA authors use it w start of CPB and sometimes postop if their SVR was reactive despite fent/benzos. (Milr and Nitroprusside didn't have same effect on SVR)

[[[ this may be outdated, ?benefit, may require more volume resuscitation because of blocked alpha R'... low SVR...., also phenoxybenzamine no longer avail, phentolamine is now used...)]]]

... *** see graphs on phenoxybenz impact on SVR,BP, CO etc***

CPB Management

-High flow CPB guided by SvO2 --> best organ Q and least metabolic acidosis/anaerobic resp

-But, Ao Arch reconstruct requires interruption of Q so there is some regional hypoperfusion

-NIRS x2 sites is also useful

-Varies by institution/pt much

-Cooling until jugular vn Sat is 100%, at which time EEG silence occurs--> max preserve cerebral oxygention during the subsequent oxygenation.

-Improved Neuro outcome w longer cooling time, pH-stat mgt during cooling, higher Hct a/p deep hyperthermic circ arrest (DHCA) <== more metabolic suppression fr hyperthermia w more DO2

-? if hypercapnia helps via metabolic suppression

-Risk after 30-40min of DHCA at 18-22C increases

-Ideally (and theoretically) continuous cerebral perfusion may avoid DHCA xx

-Rewarming/Reperfusion- O2 consuption increases. Titrate hypnotic Rx's to limit VO2 and vasc responses. Use ultrafiltration w rewarming to keep Hct>40%. Rewarm to bladder temp 36C to avoid thermoregulatory metabolic response after separation from CPB. Try to keep SVR at 12 Wood units.

-Start milrinone before separating from CPB, +/- epi to maint syst fx and HR.

-CPB pump pressure of 3.2L/m2/min --> organ perfusion P of 40mmHg (= MAP - CVP) target, while the systemic to PA shunt is occluded ==> SVRI of 12 Wood units. ...

-Once SVR is achieved and vasoactive infusion constant, then lungs are reinflated and mech vent resumed. Initial FiO2>50%, PIP 25, PEEP 3, Rate 10-20 to -_> Nl alveolar vent w/o atalectasis.

-We avoid prolonged ventilation w/o perfusion to reduce acute changes in PVR and lung injury.

-CPB is likely to be successful if: AV sat diff still Nl (20-30%), SvO2 above anaerobic threshold (30-35%)

-Low SvO2 (<40%) w high SaO2 (>80%) = high Qp/Qs, so try to decr SVR

-Low SvO2 and balanced Qp/Qs = not enough DO2--> increase inotropy, PL, Hgb, decr VO2

-...

Mechanical Circulatory Support

-Consider mechanical support if you can't get adequate DO2 despite vasoactive support and ruling out correctable problesm with the shunt.

-ECMO- VA ECMO is there is possible issue w shunt patency for lung fx

-...

Postoperative Mgt

-Unbalanced Qp/Qs, decr total CO, higher VO2, potential for myocard ischemia ==> M&M

-DO2 limited by myocardial edema, w diast dysfx and potential dvp of tamponade physiology

-Issues peak at 6-12hrs postop.

-Goal mgt: ensure enough organ oxygenation- use SvO2 and NIRS to assess this.

-Goal SvO2 >50%, cerebral rSO2 >50% and somatic rSO2>60%

-Expect an increase in VO2 by 30% when vent is stopped

Insterstage Mgt & Timing of Stage 2 Palliation

Medical Therapy

-Ch AL reduction, diuretics, +/- digoxin and anticoagulation

-ACE inhibitor- AL reduction- for Qp/Qs >2 in early postop pd, AV vlv regurg, CHF, or incr SVR; c/s adding Clonidine if still high SVR. But be careful to avoid too low of SVR (--> worsen hypoxia bc decr Qp)and cause diast hypotension so poor Qcor

-If Sx of pulm overcirc or CHF, then c/s diuretics- Lasix, but avoid intravasc vol depletion--> decr total CO and incr risk of shunt thrombosis due to hyperviscosisty

-GIve ASA ppx unless evidence of atrial/venous clot-- use Lovenox (goal anti Xa 0.7-1.2)

-Goal SaO2 >80% while awake and asleep, or c/s supplemental O2 (at their institution...)

Risk Factors for Interstage Death

-Limited circulatory reserve bc of volume loaded single ventricle w parallel circulation and cyanosis

-Sudden death bn Stage I and II is 5-15%

-Incr Risk based on anatomy, residual/recurrent lesions- Ao Atresia w diminutive Asc Ao has lowest reserve so at higher risk of late death; restrictive ASD, arch obstructoin, obstructed shunt, pulm art distortion, AV vlv regurg all incr risk

-GI/URI infections that can --> hypovolemia/acute hypoxemia incr risk

-Increased metabolic demands, poor DO2/VO2--> greater risk for mortality

Interstage Monitoring

-If the child has desaturation fr baseline, c/s anemia, resp illness, myocardial dysfx fr decr CO, limited Qp fr shunt stenosis/outgrowth.

-Hypoxemia alone might not occur early in acute illnesses that incr SVR bc Qs is decr so Qp/Qs increases

-e.g. dehydration fr gastroenteritis/poor PO intake

-Discharge pt w an infant digital scale and pulse ox for daily checks. Call MD if SaO2 <75 or >90%, wt loss 30gm, dont gain 20gm in 3 days, intake <100mL/kg/day enterally

-Started in 2000. Interstage survival improved fr 84% to 99%.

-About 1/2 breached criteria- usually bc worsening hypoxemia-stunt stenosis, outgrowth, and inomm art narrowing.

-If bc of poor wt gain- (1/3 pts)- recurr Ao arch obst, sepsis, poor PO needing NG, CHF

Nutritional Support & Somatic Growth

-Healthy infants usually double birthwt by 5mo, but HLHS pt have limited growth potential, and plateau bn 4-5mo. Usually <20gm/day (nl is 30)==> focus on caloric intake prior to discharge, take 110-130cal/kg/day w fortified formula. W monitoring, growth improved to 25gm/day.

-1/4 of pts needed a G tube

STAGE 2 Palliation: Superior Cavopulmonary Connection

-SVC anast to prox impsilat PA, takedown of prior shunts

- ==> reduce wall stress and AV vlv regurg bc u get rid of the vol overload on the single ventricle

- ==> more effic series circulation , and incr diast P w incr Qcor

-Delay of Stage 2 till 6mo bc of reports that too early--> sev hypoxemia, prolonged pl drainage, PA thrombosis, poor PA growth, early pulm AVM formation, incr mortality; BUT MA author supposes that reducing the high risk bn stage I and 2 by moing up stage 2 would increase survival.

-If the Stage 1 pts breached above criteria, they go to Stage 2 early (3.5 vs 5.5 months), though weights were similar in these early patients (bc of the wt plateau at 4mo discussed above)

-Younger pts getting Glenn needed longer mech vent, greater dur of pl drainage, and longer hosp stay, and lower O2 sats postop, but by discharge they had similar O2 sats, and w long term f/u there was no diff in late complications, w same pre Fontan hemodynamics.

-Improved activity, reserve after stage 2, lasting several years.

-Increasing cyanosis p Glenn d/o: incr lower body growth and VO2 w concomitant decreased IVC sat, and the pt dvps Venovenous collats fr high P SVC to veins that drain into the IVC or atrium. And, pts get AVMs causing intrapulm shunt so PV has less O2...,

-bc of missing "hepatic factor"

-Pulm AVMs can be reversed after Fontan

STAGE 3 Palliation: Completion Fontan

-Perform at 18mo to 4yo

-Goal: route Q fr IVC to PA

-Lateral Tunnel vs Extracardiac Conduit

-Lateral Tunnel- often do after a hemi-Fontan- a prosthetic conduit is used to make a baffel to route IVC Q to PA- not circumferential but partly made of pt's RA, so that it can grow (theoretically)

-Low level of power loss through it (so better flow)

-? increased risk of sinus nd dysfx

-potential for thrombus w systemic emboli bc of prosthetic material in RA

-Extracardiac Fontan

-conduit bn IVC and PA- easier operation, likely less SA dysfx, no presthetic material so lower thromboembolic risk

-Can't grow, so place a larger conduit (20-22mm diam), however larger/longer conduit--> lose power--> less durable

-Post op- incr risk for postop xx w HLHS pts- decr CO, incr CVP, pl effusion, ascites, thrombosis, arrhythmia

-Fenestrated Fontan- allows R to L shunt to decr CVP and improve PL and CO to systemic ventricle, but at expense of some desat.

-Fenestration- --> great survival and shorter hospital stay