=complete interruption of the aorta
-most commonly bn LCC and LSCA (type B)
-assoc w small L heart, espec LVOTO
-assoc w chrom 22 deletion/DiGeorge syndrome
Embryology-
-Prox Ao Arch is derived fr the Ao sac (fr conotruncus)
-Distal Ao Arch is derived fr the 4th embryonic arch (gives the L A arch usually)
-Isthmus is derived fr jct of 6th embryonic arch (DA) w the L dorsal aorta & 4th embryonic arch
Anatomy-
-Proximal Ao Arch = fr Innom art to LCCA
-Distal Ao Arch = fr LCCA to LSCA
-Isthmus = connects distal Ao Arch to the juxtaductal region of desc Ao
-Classification of IAA
-Type A = @ isthmus
-may see a milder form w a short fibrous chord connectin across the interruption, but w/o a lumen
-aka aortic atresia, usually easier to repair surgically
-Type B = @ bn LCCA & LSCA
-#1 type - 69-79%
-often assoc w aberrant origin of RSCA fr desc Ao
-this is assoc w subAS, bc less Q is thru the LV to asc Ao, and more thru DA to all head branches except for the RCCA
-Type C = @ bn Innom & LCCA
-rare, <4%
-Associated Anomalies
-rare to have isolated IAA
-PDA, then VSD most common assoc xx
-isolated VSD in 73% of pts
-often post malalignment of outflow septum --> LVOTO, small Ao annulus
-bicuspid Ao vlv common
-+/- prominent LV free wall muscle bundle projecting into the outflow (muscle of Moulaert)
-fibrous subAS membrane rare in neonate, but may dvp later on
-ASD common- usually stretched PFO, ? bc of L to R shunting in utero bc of the interruption w assoc LVOTO
-single ventricle in 11%
-truncus arteriosus in 10%
-also see DORV, TGA+VSD, CASD, DOLV, ccTGA
-Path
-no important impact on fetus, bc <10% of Q goes thru isthmus in a Nl fetus
-postnatally, pt is PDA dependent, so get ischemia/shock...
-Sx
-... shock as PDA closes...
...
-Rx Tx/Intervention
-PGE...
-Surgery
-Indications- Dx = indication for surgery
-measure BP above & below the obst
1) Median sternotomy
2) excise thymus
3) cannulation- Asc Ao, they also do the PA to 'optimize perfusion' espec to brain & heart in the early phase of cooling; venous cannulation at RA
4) Cool patient to 18C
5) mobilize Asc Ao & branches. If +aberrant RSCA, then ligate it and divide it fr the desc Ao origin; if it is a type B IAA, then may also want to ligate & divide the LSCA to minimize tension on the arch
6) Once pt cooled, then discontinue CPB & start cardioplegia, and remove cannulas
7) Ligate PDA and divide it at the jctn w the desc Ao. Excise residual ductal tissue fr the Ao
8) Perform anastomosis of desc Ao to asc Ao
9) fill Ao w saline thru Asc Ao cannulation, to displace Air fr the Asc Ao/arch/head vessels
10) reinsert arterial cannula, apply cross clamp across it, and recommence CPB
11) Cold reperfusion for 5 minutes, then reduce flow and fix the VSD thru PA approach or redo circ arrest if work via RA
-VSD closure
-if there is conal septal hypoplasia, then best to approach via MPA, by continuing hypothermic low flow bypass thru the VSD closure
-ASD closure
-decide pre-op if need to close the ASD
-usually close by direct suture thru a short low right atriotomy during brief pd of circ arrest
12) Rewarm & separate fr bypass
-IAA w VSD & LVOTO
-may require a Yasui bc of a LVOTO-
-direct LV outflow thru the VSD to the proximal divided MPA by a baffle
-divide the MPA just before the bifurcation
-anastomose the prox MPA to the side of the Asc Ao (bypassing the LVOTO...)
-place an RV-PA conduit, preferably Ao or pulm homograft
-alternatively, u can use a BT shunt (~ to a Norwood w IAA repair additionally) but not preferred bc both ventricles are of good size...
Surgical Results
-Advantages of 1 stage, primary repair, with direct anastomosis
-dramatic outcome improvement fr 1974 to 1987 (2 wk mortality 50% reduced to 10%)
-bc of pre-op resuscitation, use of direct anastomosis rather than a conduit
-Complication
-Early
-bleeding, more likely if excessive tension at arch anastomosis bc inadequate mobilization of Asc/Desc Ao
-tissue is more friable if pt was acidotic pre-op --> easier bleeding
-L recurrent laryngeal & phrenic nerve injury - phrenic n injury common at Boston after placement of an Asc to Desc Ao conduit, ?bc direct compression of the n by synthetic material. Now that they do direct anastomosis, it is rare.
-Late
-Pressure Gradient at the Arch
-if a graft tube was used as a neonate, they will get a gradient (/ >30mmHg) bc of somatic growth. & grafts may dvp pseudointima--> more obst
-freedom fr obstruction 55% at 5yrs postop
-if direct arch anastomosis, pts were more likely to have obstruction (!)
-freedom fr obstruction 40% at 18months postop (!)
-BUT, balloon dilation can relieve the gradient well in most kids (vs inevitable conduit replacement for grafts)
-Boston experience- freedom fr re-intervention for arch obst was 86% at 3yrs postop if direct anastomosis
-LVOTO
-a top xx
-Ao vlv diameter = most Sn predictor of xx- all pts w Ao annulus <4.5mm had late LVOTO (!)
-ref 35- indexed cross sectional area of subAo area was most useful predictor in one study
-CHSS large study--> performing a conal septal resection or DKS had higher neonatal mortality, even after MV analysis for L heart hypoplasia..., but it was multiinstitutional w wide variety of outcomes...
-ref 3- small study (n=33) who underwent conoventric VSD + IAA repair, only 58% free of LVOTO (=P gradient 40mmHg) at 3yrs postop
-CHSS study- 77% freedom from reop at 3yrs postop
-LVOTO morphology varies, so surgical Tx will have to be individualized...
-may need Ao valvotomy, modified Konno (ventricular septoplasty) via RV incision
-may need Ross/Konno if Ao annular hypoplasia and tunnel subAS
-DiGeorge Syndrome
-absent/severe hypoplasia of thymus seen only w type B IAA
-need CaCl supp postop, but not post discharge
-L Bronchial Obstruction
-usually passes under the arch of the Ao
-if direct anast is performed w/o enough mobilization, may --> bow string effect on LMB--> air trapping in L lung w hyperexpansion seen on CXR, confirm w bronch/CT/MRI
-may require surgeon to place a conduit bn Asc & Desc Ao or do an aortopexy to sternum