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Chapter 45Utility of Computed Tomographic Coronary Angiography Post Coronary RevascularizationSANKAR NEELAKANTAN • SANJAYA VISWAMITRA • SRIKANTH SOLA

Goals of imaging in post-CABG patients:1. Todelineatetheanatomyofcoronarybypass

graftsandnativecoronaryarteries2. Toreassesstheanatomyofsubclavianarteries

for left and right internal mammary artery(LIMAandRIMA,respectively)grafts

3. To guide management (PTCA vs. redo CABGvs. optimal medical therapy) in cases wherethereisgraftfailure

4. ToreassesstheanatomyofsubclavianarteriesforLIMA,RIMAgrafts

5. ForpatientsplannedforredoCABG,tostudythe relationship of cardiovascular structures/coronarybypassgraftstothesternumforredosternotomy

6. Toevaluatetheextentandprogressionofath-erosclerosis,particularlyatheroscleroticcalcifi-cationinascendingaorta

7. To assess postoperative complications likegraftthrombosisandocclusion,graftmalposi-tion,graftvasospasm,graftaneurysm,pericar-dialandpleuraleffusions,sternalinfection

8. Complications in the immediate postopera-tive period with unsuspected noncardiacfindings, including pulmonary embolism,pulmonary nodules, pneumonia, mucouspluggingandpneumothorax

Graft evaluation:All grafts are individually assessed at the proxi-mal anastomosis, distal anastomosis, graft body(orgraftproper),distalnativearteryandremain-ingnativearteriespreferablyusingcurvedmulti-planarreconstruction,3Dvolumerenderingandmaximumintensityprojectionimages.Also, lookforsequentialor jumpgraft,positionofthegraft inrelationtothesternumandinci-dentalfindingswithlargerfieldofview.

BACKGROUND

Coronaryarterydisease(CAD)istheleadingcauseofdeathanddisabilityworldover.Therehasbeenanalarmingincreaseoverthepasttwodecades inCAD prevalence and cardiovascular mortality inIndia and other south Asian countries. Primarytreatment protocol for CAD involves myocardialrevascularizationprocedures,namelycoronaryby-passsurgeries(CABG)andpercutaneoustranslumi-nalcoronaryangioplasty(PTCA)withstenting.

Patientspostrevascularizationcanpresentwithrecurrentsymptoms,thisoutcomeisgenerallyasaresultofgraftocclusion,in-stentrestenosis(ISR)ordenovolesions1.Thelong-termprognosticfactorsforsurvivalaftermyocardialrevascularizationaredependent on the patency of the bypass graft/stentsandnativeCADprogression.

Coronaryangiographyisthegoldstandarddiagnos-ticmethodforassessingthestatusofcoronarygrafts/stents.Itisaninvasiveandexpensivetechniquewithassociatedcomplications,whichareuncommon,butsometimesserious.However,thedevelopmentofso-phisticated multidetector computed tomography(MDCT) technology (64-slice or better) with three-dimensional(3D)multiplanarapplications,highspa-tial and temporal resolution, lower radiation andcontrastdosehasenabledaccuratenoninvasivevisual-ization of coronary grafts/stents with submillimetreprecisionwithinasinglebreath-hold2(Figs45.1–45.4).

CORONARYARTERYBYPASSGRAFTING

Computedtomographiccoronaryangiography(CTCA)isparticularlyeffectiveinstudyingbypassgraftsduetotheir largesize, lowerdegreeofcalcificationsandde-creasedmotionwhencomparedtonativevessels.

376 SECTION V — Cardiac Imaging

Imaging considerations for bypass grafts3,4:Saphenous vein graft (SVG): SVGs [alsoreferredtoasreversedSVGs(RSVGs)]aretypicallyattachedproximallyontheanteriorwalloftheas-cending aorta and distally below the stenosis orobstruction.Forgraftstotheleftanteriordescend-ingartery(LAD)orleftcircumflexartery(LCX)ter-ritories,aproximalanastomosisismadeontheleftsideoftheaortaandstabilizedonthemainpulmo-naryartery.Inthecaseofgraftstotherightcoronaryarteryterritory,thesaphenousveinisanastomosedtotherightsideoftheaorta,permittingittocoursetowardstherightatrioventriculargroove.Chance forocclusion isaround50%inthefirst5years.Graftbodyocclusionisrelativelycommon.Internal mammary artery (IMA): The IMA

hasbecometheconduitofchoiceforrevascu-larization of obstructed coronary arteries. Thegraft is conventionally used in situ from itsproximaloriginattheleftsubclavianwithdis-talanastomosisbelowtheoccludedLADordi-agonalbranches.Thesegraftsarepreferredovervenousgraftsas theyare larger incalibre, lesspronetoocclusionandmorepressureresistant.Graftstenosisismostlynotedatthelevelofthedistalanastomosis.Thereisapossibilityofclipartefacts at this region; however, if the graftbodyispatent,thentheclipartefactisignoredandthegraftisassessedaspatent.RIMAgraftistheonlyexceptiontothis.

Radial artery (RA): It is harvested from thenondominant arm and used in combinationwithotherarterialgraftsorasanindependentgraft.TheRAisgenerallyusedasanalternativeto a venous graft or when a third graft isrequired.Itismostcommonlyusedasaninde-pendentconduittoperfusetheleftcardiacter-ritory. It canbeused,however, aspartof aYconfigurationoraconduittoperfusethedistalright coronary artery (RCA) or posterior de-scendingartery(PDA).RAgraftsareprone fordiffuse spasmandcanappear as a diffuse long segment narrowing.Themostcommonsiteforfocalstenosisisthedistalanastomosis.

Other arteriesliketherightgastroepiploic,ulnar,left gastric, splenic, thoracodorsal and lateralfemoralcircumflexarteriescanbeused incaseswherenoalternativearterialconduitsarepresent.

Result interpretation:1. If all grafts are occluded, evaluate the native

coronary arteries and consider redo CABG orlimited PTCA, as flow could be reestablishedpostintervention.

2. If the graft is occluded and the distal nativevesselisalsooccluded,noinvasivemanage-mentiswarranted;thepatientshouldbeputonmedicalmanagement.

3. IfallnativecoronaryarteriesareoccludedandoneCABGgraftispatent,thisvesseliscalledlast remaining patent artery (LRPA) and is ahigh-risksituation;considerpercutaneouscor-onaryintervention(PCI)incaseofstenosis.

CORONARYSTENTING

PCIinvolvingtheplacementofstents is themainnonsurgicalprocedureformyocardialrevasculariza-tion. Newer generation MDCT scanners enabledirectvisualizationandassessmentofstentlumenandassessmentofin-stentpatency.Goals of imaging in patients with coronary

stents:1. To visualize and accurately assess stent pa-

tency,ISRorneointimalhyperplasia.2. Tolookforstentfracture.3. To guide repeat interventions in case of

stentfailure.Challenges with MDCT evaluation of coro-

nary stent patency1,5:The degree of artefacts varies with the materialcomposition of the stent used. Most stents aremadeofstainlesssteel,butnewergenerationofstentsaremadeoftantalum,cobaltalloys,plati-num,nitinolandtitanium.Stentsmadeoftanta-lumcreatethemostintensebeamhardeningar-tefacts,whereastitaniumandnitinolstentscausetheleastartefacts.Stent design and strut diameter can affect themagnitude of artefacts and limit accuracy inevaluationofcoronarystentpatency.Stentdiameterisanimportantfactorin-stentlu-menassessment.Ingeneral,stentswithadiame-ter3.5mmarebettervisualized.

Image analysis for post-PCI and stented pa-tients:Using sharp kernel and wider window width(widthof1200),incaseofdualenergyCTtech-nology,subtractioncanbedoneforspecificstentcompositions,whichhelpsin-stentdelineation.Coronarystentsareconsideredoccludedifthereis complete absence of contrast inside the stentlumen with decreased or absent distal runoff.Visualization of contrast in the vessel distal tothe stent does not necessarily indicate patencybecauseitmaybeduetoretrogradefilling.There-fore, reduced contrast enhancement distally im-pliesocclusionorretrogradeperfusion1.

377Chapter 45 — Utility of Computed Tomographic Coronary Angiography Post Coronary Revascularization

Restenosis isacritical factor for the long-termsuccessofPTCAandisdefinedasareductionin50% of the stent lumen diameter. ISR is lessfrequent in drug-eluting stents (,10%) com-paredtouncoatedmetallicstents(almost40%).Acutestentthrombosiscanoccurduringthe24hafter intervention,whereas subacute thrombosistypicallyoccursbetween1and30daysafterim-plantation of the coronary stent. Drug-eluting

stentsareassociatedwithdelayedin-stentthrom-bosis, usually after 30 days of stent placement.Balloonangioplasty is themostcommonproce-dureforthetreatmentofISR1,5.Also, rule out stent fracture, which is identifiedby fragmentation and/or migration of the stent.Figs45-1to45-4demonstrateillustrativeexamplesof the utility of CT coronary angiography in pa-tientswithpreviouscoronaryrevascularization.

A

DISTAL SVG SEVERE STENOSIS

SVG TO PDASEVERE STENOSISIN DISTAL GRAFT

P

I BI

C

ATRETIC LIMA

NATIVE LAD

NATIVE LAD SHOWSDIFFUSE SEVERE DISEASE

Figure45-2. A 57-year-old man (known case of CAD, status post CABG in 2005) presented with exertional dyspnea class II since 3 months. Reformatted and VRT images showing distal severe stenosis in SVG to PDA; LIMA to LAD atretic with diffuse severe disease in native LAD. RA-obtuse marginal 1 (OM1) also showed subtotal occlusion. In this patient with prior CABG, since native PDA was the LRPA with focal stenosis of body of SVG graft, redo CABG was deferred. Hence, invasive coronary angiogra-phy and PTCA was advised.

A: Coronal reformatted image

Occlusion of SVGto PLB graft justdistal to its orgin

RCA

PDAPLVB

RSVGGRAFT

SITE OFANASTOMOSIS

Angle: 56.0

3 cm

Ex: Apr 04

Aorta

B, C: Volume rendered 3D images (VRT)

Figure45-1. A 62-year-old man (status post CABG 2010) presents with angina. In this patient with prior CABG, CTCA showed patent LIMA to LAD, SVG to first diagonal and SVG to PDA. There was evidence of occlusion in the proximal aspect of SVG to posterior left ventricular branch (PLB or PLVB) as shown in the VRT image (B); however, the native PLVB distal to anastomosis was patent. Hence, redo CABG was advised.

378 SECTION V — Cardiac Imaging

FUTURECONSIDERATIONS

Recentadvancementsinimagingtechnologyhavedramatically expanded the capabilities of CT fornoninvasivecoronaryimaging.Thenewer256-and320-slice scanners have an increased longitudinalcoveragewithimprovedtemporalresolution.Theseimprovementsaidinreducingartefactsduringim-ageacquisition.

Dual-source CT has emerged in evaluation ofcoronary arteries in patients with elevated heartratesandarrhythmiaswhilesimultaneouslyassess-ing global ventricular function, regional wall mo-tionandcardiacvalves.Theuseofprospectivegat-ing has led to a reduction in radiation dose in

LIMA GRAFT

NATIVE LADOCCLUDED

SVG TO D1

PROXIMAL LCX OCCLUSION

LCX STENT

SVG TO RI

Figure45-4. A 57-year-old man presented with angina on exertion (status post CABG in 2007). In this case, the LCX stent showed proximal occlusion; SVG to D1 and SVG to ramus intermedius (RI) were completely occluded. Hence, LIMA to LAD was the LRPA; however, LAD showed proximal occlusion. Redo CABG/PCI options are not available in this case. So this patient was advised optimal medical management.

patients compared with retrospective ECG gatingwithout compromising the diagnostic accuracy ofcoronaryCTCA6.

Arecentdevelopment isCTfractionalflowre-serve (FFRCT) that isused todetermine the func-tional significance of stenotic/occlusive lesionsusing CT data. Potentially, the addition of thistechnology could make CTCA a comprehensivenoninvasive method in coronary assessment,comparabletothemoreinvasivecoronaryangiog-raphy7.

RoleofCTperfusionandmetabolicimagingwillprovidecombinedanatomicalandfunctionalinfor-mation while evaluating revascularized hearts,whichwillaidindecisionmaking.

A B C

RIMA GRAFT

LAD

RCA

RSVG GRAFT

Figure45-3. A 55-year-old man (known case of CAD) presented with atypical chest pain since 1 month. 3D volume rendered images (A, B) showing origin of RIMA (red arrow) and RSVG (yellow arrow) in a patient with dextrocardia and sided aortic arch. Coronal oblique reformatted image (C) showing occlusion of RSVG to OM graft (red arrow).

379Chapter 45 — Utility of Computed Tomographic Coronary Angiography Post Coronary Revascularization

CONCLUSION

MDCTcoronaryangiographyisanaccurateandes-sentially noninvasive tool for the assessment ofcoronaryarterybypassgraftsandstents.Recentandfuturetechnologicaladvancescanfurtherimproveimagequalityandprovidecriticalprognosticinfor-mation.

RefeRences

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2. Baumüller,S.,Leschka,S.,Desbiolles,L.,Stolzmann,P.,Scheffel,H.,Seifert,B.,etal.(2009).Dual-sourceversus64-section CT coronary angiography at lower heartrates:comparisonofaccuracyandradiationdose.Radi-ology,253(1),56–64.

3. Sun,Z.,&Sabarudin,A.(2013).CoronaryCTangiogra-phy:Stateoftheart.WorldJournalofCardiology,5(12),442–443.

4. Mahnken,A.H.(2012).CTimagingofcoronarystents:Past,present,andfuture.ISRNCardiology,2012[ArticleID139823,12pp.].

5. Han,R.,Sun,K.,Lu,B.,Zhao,R.,Li,K.,&Yang,X.(2017).Diagnostic accuracy of coronary CT angiography com-binedwithdual-energymyocardialperfusionimagingfordetection of myocardial infarction. Experimental andTherapeuticMedicine,14(1),207–213.

6. Nørgaard,B.L.,Jensen,J.M.,&Leipsic,J.(2015).Frac-tionalflowreservederivedfromcoronaryCTangiogra-phyinstablecoronarydisease:Anewstandardinnon-invasivetesting?EuropeanRadiology,25(8),2282–2290.

7. Meinel,F.G.,Wichmann,J.L.,Schoepf,U.J.,Pugliese,F.,Ebersberger,U.,Lo,G.G.etal.(2017).Globalquantifica-tionofleftventricularmyocardialperfusionatdynamicCT imaging: Prognostic value. Journal of CardiovascularComputedTomography,11(1),16–24.