L-Transposition of the Great Arteries (L-TGA) (M/A)

Congenitally Corrected TGA -- L-TGA (MA52)

-aka isolated ventricular inversion, double discordance, physiologically corrected transposition, L-TGA

-->

-systemic veins to morph RA, connected by a MV to an LV, connected to a PA which is transposed

-pulmonary vns to morph LA, connected by a TV to an RV, connected to an Ao which is transposed

--> AV & VA discordance

-can occur w situs solitus or situs inversus

-NET, systemic venous blood gets to lungs and pulmonary venous blood gets to body, so it's all good, except that the hemodynamics are NOT normal, even if no other assoc xx

Epi:

-Uncommon, 0.05% of CHD;

-Genetics+Environmental influence

Embryology:

-primitive cardiac tube anchored at the sinus venosus end and the TA end, loops to the LEFT (L-looped) (normally it loops to the right- d-looped)==> morph LV now on R side, and morph RV on L side.

Morphology:

-95% situs solitus

-25% dextrocardia/mesocardia

-Ventricular Topology: morph RV on left, morph LV on right ==> Left hand ventricular looping (by Dr. Anderson's palm technique to ID topology - only L hand can fit in RV w thumb in inlet, fingers in outlet and palm on IVS surface)

-LV & RV might be in a more sup-inf relationship bc of further twisting during looping

-IVS tends to be more sagittal/horizontal--> malalignment of atrial septum and ventricular septum (seen often w AV discordance)

-Atrial & Ventricular septa should meet at crux of heart, but the atrial septum continues ant/rightward, it will deviate from the ventric septum--> gap fr malalignment of atrial septum==> VSD, and variable outflow sizes and conduction system placement.

-R sided AV valve = Mitral valve- 2 pap muscles, no insertion onto IVS

-10% of MV's have signif abNlies

-L sided AV valve = Tricuspid valve- often abNl, w septal leaflet brought into the gap made by the septal malalignment at the membranous septum, and this leaflet might form the post wall of the LVOT.

-AV discordance is assoc w TGA, and leftward anterior position of the Ao valve relative to pulm valve

-leftward anterior position of Ao might also occur w complete TGA, DORV, anatomically corrected malposition, crossed AV connections, superoinferior ventricles, and univentricular connections

-LVOT is deeply wedged bn the L and R AV valves and thus more vulnerable to obstruction;

-Pulm vlv usually has fibrous continuity with mitral valve

-Leftward anterior aorta is supported by a muscular infundibulum, and NO fibrous continuity w either AV valve. RVOTO and Ao obstruction do occur; +assoc w AV vlv regurg; Ao might have some degree of obstruction.

Associated Lesions:

>90% ccTGA have assoc xx

-VSD

-80% have VSD- perimembranous, bc of atrial/ventric septal malalignment - they are subpulmonary, and next to the septal leaflet of the L sided TV

-often large, w ant extension, allowing for intraventricular tunneling

-Pulmonary Outflow Obstruction

-30-50% have outflow tract obstruction fr the morph LV, usually in assoc w large VSD

-1/3 of pts w VSD+Pulm OTO have abNl TV morph too

-LVOTO might be muscular bc of wedging of the supulmonary outflow tract bn the infundib septum and ventricular free wall, and bc of the R sided ventrculofundibular fold (causing obst)

-fibrous tissue fr the membranous septum might also cause some LVOTO

-Tissue tags fr TV or MV (common), or PV stenosis can also cause obstruction

-Tricuspid Valve (left sided) Lesions-

-90% have some type of TV xx

--> valve dysfx, etc

-dysplastic valve- #1 xx, +/- septal/post leaflets displaced, similar to Ebstein anomaly of L sided TV

-Both morph TV and the MV can straddle the ventric septum

-Coronary Artery Anatomy-

-Usually originate from the post facing sinuses of Ao vlv

-If atrial situs solitus and ccTGA, the cor arts have mirror image distribution

-R sided CA has distribution of the morphologic LCA and the main R sided CA bifucates into a circ and ant desc branch, while the L sided CA runs in the left AV groove, to --> infundib and marginal branches

-CA's can be variable

-single CA was common, with 61% having a large cor branch that crosses the RVOT, which is important if pt was to get a Rastelli...

-knowing CA anatomy is crucial to double switch repair...

-Specialized Conduction Tissue-

-AbNl conduction system, that can be unstable

-SA nd lies in Nl spot in atrium

-AV conduction tissue is abNl

-2 AV Nds, w a Nl post AV nd at apex of Koch Triangle but NO AV bundle, and an AbNl R ant AV Nd in that yields the Penetrating Bundle, in the ant-sup area lateral to the pulm/mitral valve continuity, under the RAA opening. AV bundle has a superficial course along ant aspect of the subpulm outflow tract, and superior LV wall, into the upper IVS fr which it descends and branches. If thre's a VSD, the ant AV nd courses along its ant-sup margin

-This all probably occurs bc usually the AV bundle dvps fr the Nl AV nd, at the top of the IVS, but bc of the atrial/ventric septal malalignment this can't happen. So, pts w pulm atresia or signif PS will have less a-v septal malalignment and thus are more likely to have Nl conduction system.

-So, you can correlate LVOT size (e.g. subpulm OT size on R side of hrt), with degree of septal malalalignment, and presence of Nl AV conduction tissue.

-Some pts have conduction tissue straddling both ant sup and inf post margins of the VSD, w a slinglike bundle over the ant margin fo the VSD that connects both AV bundles...

Sx/Si:

-ASx as child, then Sx as adult; or Sx earlier fr assoc Sx

-May present as infant w bradycardia +/- heart failure bc of heart block, tachyarrhythmia, cyanosis bc of low Qp, or heart failure

-CHF can occur bc of arrhythmia, large VSD, dysplasia/displaced TV w TR, Ao obstruction

-Older kid may have loud S2

-If you have a pt w Sx concerning for MR, then c/s ccTGA

ECG:

-normal P axis, w +P in I, II, III, avL, avF, and neg in avR, regardless of heart position in heart

-ventricles: activation starts in IVS and then goes fr L to R and slightly ant'ly--> initial Nl Q wave in precordials w qR in V6 and Rs in V1. No Q waves in L precordials is sometimes seen in Nl kids, but 1/5 of neonates might not have a Q in V6.

-Sagittal IVS - L post to R ant, and both bundle branches are inverted so the sequence of activation is oriented fr R to L, and sup/antly direction--> reversed Nl Q wave pattern in precordials, w Q waves in the R precordials but absent in L precordials. (not well seen w dextroposed heart or assoc xx...)

-ccTGA ECG: Q waves distrib in precordials w QS in R precordials, Large Q wave in III and avF, and LAD

--complete HB seen in 10% at onset of Sx, but increases over time, even after surgery

CXR:

-In older pt- check for levocardia, atrial situs solitus, side by side TGA or oblique TGA w Ao to the left; --> LU mediast border w convex prominence at the middle/upper part w mild convexity where you'd expect the pulm trunk- this is bc of the levo positioned Asc Ao (see arrows in pic), which starts fr morph RV on the L side

Echo:

-check situs- abdominal GA's

-situs inversus--> Ao to R of spine, IC to L of spine, RA on L (+in 5% of ccTGA)

-situs ambiguous--> interupted IVC or Ao and IVC on same side of spine (these are NOT true ccTGA)

-Subcostal LA- check heart position- 25% have dextro/mesocardia

-r/o other abNl AV connections- criss cross AV, superior inf ventricles...

-check for RV morph vs LV morph- apical displacement of teh AV valve of the RV relative to LV, trileaflet AV valve versus a bileaflet AV valve, chordal attachments of the RV AV valve directly to septum, moderator band (RV), irregular mural endocardial surface of morph RV vs smoother surface of morph LV, round/triangle RV cavity vs elongated/ellipsoidal LV

-PSLA- see more parallel GA's = TGA

-confusing bc the IVS is often horizontal, espec confusing if large perimem inlet VSD, bc pulm valve can be seen related to either AV valve, so unsure where the VA connection is...

-check source of outflow tract obstruction to Ao or PA

-check for outflow tract obst w doppler

-PSSA- see Ao w cor arts- see Ao L and ant relative to bifurcating PA

-confirm VA connection is discordant by sweeping in short axis

-confirm orientation of IVS

-confirm the AV valve leaflet anatomy

-confirm the papillary muscles

-Ap4C- tilt anteriorly to see how the pulm outflow tract fr R sided LV is deeply wedged bn the 2 AV valves

-check AV valve anatomy - check for Ebstein malformation of the leftsided tricuspid valve

-check for AV valve regurg

-check for perimembranous inlet VSD

-Check for ASD (12% of pts)

-check for AV valve straddling, inflow obstruction... if +straddling AV vlv, c/s ventric hypoplasia

-High L PS view- sagittal plane, (ductal view)- check for PDA and open up Ao Arch- check for R Ao Arch

-Suprasternal view- doesn't show Ao as well

-check for VSD- >60% +, and may be partly occluded by TV septal leaflet, and allow for straddling of TV

-check on PSSA, Ap4C, Subcostal

MRI:

-good for checking RV fx

Cath:

-often needed preop

-note cath course in GA's

-increased risk of AV black w cath bc AV nd/condctn sys is anterior and intrinsically fragile, espec when in the PA

-have transvenous pacing ready...

-indications: check LVOTO, L to R shunting magnitude, responsiveness to Pulm Vasc Bed to challenges

-Angiography:

-must do echo first to establish Dx

-see horizontal IVS

-...