Indications for Bypass Surgery | Journal of Ethics

The chief anatomical indications for CABG are the presence of triple-vessel disease, severe left main stem artery stenosis, or left main equivalent disease (ie, ... Skiptomaincontent VirtualMentor.2004;6(2):78-81.doi: 10.1001/virtualmentor.2004.6.2.cprl1-0402. Citation PDF Altmetric email   Thedefiningfeatureofcoronaryarterydiseaseisafocalnarrowinginthevascularendothelium,whichimpedestheflowofbloodtothemyocardium.Atheroscleroticplaqueformstheprincipallesion,whichiscomposedofanecroticcentercontainingcelldebris,cholesterol,andcalcium.Outliningthenecroticcenterisafibrouscapmadeofproliferatedsmoothmusclecells,connectivetissue,andlipids. Althoughtherearemanyidentifiableriskfactorsforatherosclerosis,noneofthemconstitutesaknownmechanismforthepathogenesisofcoronaryarterydisease.Thewidelyaccepted"responsetoinjury"theoryproposesthattheinitialstimulusisaninjurytothearterialendothelium.Damagedendothelialcellsreleasevariouschemotacticfactorsandstimulatethedepositionoffattymaterial.Iftheprocessisnotreversed,maturefibrousplaqueswillobstructthearteriallumen. AnginaPectoris Anginapectorisisthemainclinicalconsequenceofdecreasedbloodflowinthecoronaryarteries.Itischaracterizedbychestpainorpressureoftendescribedbypatientsascrushingorsqueezing.Oneofthemostimportantfeaturesofanginaisthatitistypicallybroughtonbyphysicalexertion. TheNewYorkHeartAssociation(NYHA)hasdevelopedafunctionalclassificationsystemthatiscommonlyusedbyphysicianstoassesstheseverityofanginarangingfromClassIangina,whichisbroughtononlywithunusuallystrenuousactivity,toClassIV,anginaexperiencedwhileoneisatrest. Thereareseveraltypesofanginalsyndromes.Stableanginadescribesapredictablepatternofanginalsymptoms.Unstableanginaismoreworrisomeasitmaypresageamyocardialinfarction.Anginaisclassifiedasunstablewhenthereisachangeineitherthefrequency,duration,orseverityoftheattacks.Symptomsoccurringatrestarealsoconsideredunstableandareparticularlyalarming.Prinzmetal'sanginaisavarianttypeofpain,typicallyoccurringatnight,whichissuspectedtooccurasaresultoftransientcoronaryspasm. Symptomlesscoronaryheartdiseasedoesoccur,especiallyindiabeticpatients.Withoutthewarningsymptomsofangina,thefirstpresentationofcoronaryheartdiseasemaybeapotentiallydeadlyheartattack. DiagnosisofAnginaPectoris Patienthistoryalonecanleadquicklytoadiagnosisofanginapectoris,andnoninvasivetestingoptionscanconfirmthediagnosis,preferablybymeansofastresstest.Arestingelectrocardiogrammaybetakenbutislikelytobenormalintheabsenceofpainandinpatientswithnoprevioushistoryofmyocardialinfarction.Stresselectrocardiography,recordedwhilethepatientperformssomesortofphysicalexercise,helpsdetectandevaluatetheseverityofmyocardialischemia.Adetaileddiscussiononthewidevariabilityinthesensitivityandspecificityofexercisestresstestingisavailableinthe"ACC/AHAGuidelinesForExerciseTesting," theAmericanCollegeofCardiology/AmericanHeartAssociationtaskforcereportonexercisestresstesting[1]. ThestandardexercisestresstestisconsideredlowyieldincertainpatientsincludingthosewithexistingEKGabnormalitiessuchasleftbundlebranchblocksorleftventricularhypertrophy.Anuclearstresstestisanexcellentalternativetothestandardstresstest.Thallium,aradioactivesubstance,isinjectedintothebloodstreamduringpeakexerciseandagammacameraisusedtovisualizetheheartanditsbloodsupply.Pharmacologicstresstestsutilizingdobutamine,adenosine,anddypyridamoleareotheralternativesandaresuitedforpatientswhoareunabletoexerciseorwhohavedeepvenousthrombosis. Cardiaccatheterizationisthegoldstandardtestforthediagnosisofcoronaryarterydiseaseandisusedtodeterminewhethermedicalorsurgicaltherapyismoreappropriateandtoplanrevascularizationsurgery[2].Whenthepatient'shistorysuggestscongestiveheartfailureorwhenarevascularizationprocedureisbeingcontemplated,anechocardiogramisappropriate[2]. MedicalManagement Mostcasesofchronicstableanginainpatientswhoareconsideredtobeatlowriskformyocardialinfarct(ie,single-vesseldiseasenotaffectingtheleftmainstemartery)canbemanagedwithoutsurgicalintervention.Drugtherapycanreduceischemicpain,minimizethefrequencyandseverityofischemicepisodes,preventseriouscomplications(myocardialinfarction),andimprovethequalityoflife.Foragoodoverviewofthemedicalmanagementofchronicstableangina,seeanarticlepublishedintheAmericanFamilyPhysicianinJanuary2000[2].Importantitemsinthedrugtherapyarsenalare: Nitrates, Beta-adrenergicblockers, Calciumchannelblockers, Aspirin,and Lipid-loweringagents. Themanagementofunstableanginaoranginaatrest(ClassIV)initiallyinvolvestreatmentwithbedrest,intravenousheparin,andaspirin.Whenthepatientisstable,cardiaccatheterizationisperformedtoassessthedegreeofstenosisandplanrevascularizationprocedures. PercutaneousCoronaryInterventions PercutaneousCoronaryinterventions(PCI)areinvasiveproceduresduringwhichasmallballoon-tippedcatheterisinsertedintoeitherafemoralorbrachialarteryandthreadeduptotheobstructinglesioninthecoronaryartery.Whentheballoonisinflated,theplaqueisflattenedagainsttheendothelialwall,thearteryisdilated,andbloodflowtothemyocardiumisincreased.Smallwirestentscanbeinsertedatthesitetomaintaindilationandpreventrestenosis[3]. CoronaryArteryBypassSurgery Moreseriouscasesofcoronaryarterydiseaserequirecoronaryarterybypassgraftsurgery(CABG),aproceduredesignedtorestorebloodflowtothemyocardium.Performedsincethelate1960s,thisisnowoneofthemostcommonoperationsintheUnitedStates—upto500,000aredoneyearly. IndicationsforCoronaryArteryBypassGraftSurgery The1999GuidelinesforCABGSurgerydevelopedbytheAmericanCollegeofCardiologyandtheAmericanHeartAssociationlistthefollowing6conditionsasindicationsforCABGinpatientswithstableangina[4]: 1.Significantleftmaincoronaryarterystenosis. 2.Leftmainequivalent:significant(70percent)stenosisoftheproximalleftanteriordescending(LAD)andproximalleftcircumflexarteries. 3.Three-vesseldisease. 4.Two-vesseldiseasewithsignificantproximalLADstenosisandeitherejectionfraction<0.50ordemonstrableischemiaonnoninvasivetesting. 5.One-or2-vesselstenosiswithoutsignificantproximalLADstenosis,butwithalargeareaofviablemyocardiumandhigh-riskcriteriaonnoninvasivetesting. 6.Disablinganginadespitemaximalnoninvasivetherapy,whensurgerycanbeperformedwithacceptablerisk. Duringtheprocedure,thecloggedcoronaryarteryis"bypassed"bygraftingavessel(usuallythepatient'sownsaphenousveinorinternalmammaryartery)aroundthelesion.Thesurgerytraditionallyrequiresthattheheartbestoppedwhilethepatientisconnectedtoaheart-lungmachine,whichoxygenatesandcirculatesthebloodinplaceofthepumpingheart.Innovationsinsurgicaltechniqueallowforminimallyinvasivebypasssurgeryandavoidtheuseoftheheart-lungpump. ThechiefanatomicalindicationsforCABGarethepresenceoftriple-vesseldisease,severeleftmainstemarterystenosis,orleftmainequivalentdisease(ie,70percentorgreaterstenosisofleftanteriordescendingandproximalleftcircumflexartery)—particularlyifleftventricularfunctionisimpaired.Overall,scientificstudieshaveshownthatCABGimproveslong-termsurvivalinthesehigh-riskpatients,whilealsorelievingtheirsymptomsofangina[4]. ThebenefitsofCABGarenotuncontested,however.Forexample,theBypassAngioplastyRevascularizationInvestigation(BARI)wasalarge,randomizedcontrolledtrialwhichlookedatmortalityinpatientswithmultivesseldiseasewhoweretreatedwitheitherCABGorthelessinvasivePCI.Nostatisticaldifferenceinsurvivalrateswasfoundateither5or10yearswithasingleexception.DiabeticpatientshadastatisticallysignificantlowermortalitywithCABGat10years[5].Inthe1990s,largermeta-analysescomparingshorttermoutcomes(1-3years)ofPCIversusCABGalsofoundnosignificantdifferenceinratesofdeath[6].ItisimportanttonotethatBARIisoftencriticizedforitsinclusioncriteria.Sixtypercentofpatientsinthetrialhadmoderate2-vesseldisease.SuchpatientswouldnotbeexpectedtobenefitfromCABGtothesameextentasthosewithmoresevereanatomicaldisease. What,then,canwesayaboutthebenefitsofinvasivetherapiessuchasPCIandCABG?Invasivetherapyisgenerallynotrecommendedforlow-riskpatientswithsingle-vesseldiseaseunlesstheysuffersignificantlyfromanginaorhavefailedmedicaltherapy. Low-riskpatientswithsingle-vesseldiseasewhoarenotachievingdesiredanginalreliefwithmedicaltherapywilllikelyimprovebothsymptomsandqualityoflifewithPCI.CABGhasnotbeenshowntoimprovesurvivalinlow-riskpatientswithsingle-vesseldiseaseexceptthosewithleftmainorleftmainequivalentdisease[3].Second,thosepatientsathighriskforcomplications(duetheanatomicseverityoftheirdisease)whoundergoCABG,willseeareductionintheirriskofdeath[3].Also,inthesehigh-riskpatients,CABGdeliversamoreimmediateimprovementinqualityoflifewhencomparedtoPCIandrequiresfewerrepeatprocedures[3]. Formoderateriskpatients(ie,2-vesseldisease),eitherinvasiveproceduremaybeused.Decidingbetweentheprocedurescanbedifficultandshouldbebasedonpatientpreferenceandriskfactoranalysis.However,anewmeta-analysisstudy(whichincludestheBARItrial)preparedbyphysiciansatTufts-NewEnglandMedicalCentersuggeststhatCABGisassociatedwithbothdecreasedriskofmortalityandgreatersymptomimprovementat5yearswhencomparedtoPCI.Theresearchersfounda1.9percentabsolutesurvivaladvantagefavoringCABGat5years.PatientsundergoingPCIweremorelikelytorequirerepeatproceduresandhavemoresevereanginalsymptomscomparedtothosewhounderwentbypasssurgery[7]. Clearly,preventionofatheroscleroticcoronaryarterydiseaseshouldbeatoppriority,giventherisingincidenceofthisdiseaseasthepopulationages.Bothmedicalandsurgicalapproachestothemanagementofcoronaryarterydiseaseneedtobesupportedbylifestylechanges. ReadMore Chronicdisease/Cardiovasculardisease, Ethics/Practice, Evidence-basedpractice/Effectiveness References GibbonsRJ,BaladyGJ,BeasleyJW,etal. ACC/AHAguidelinesforexercisetesting.AreportoftheAmericanCollegeOfCardiology/AmericanHeartAssociationTaskForceonPracticeGuidelines(CommitteeOnExerciseTesting). JAmCollCardiol. 1997;30(1):260-311. ViewArticle PubMed GoogleScholar ZangerDR,SolomonAJ,GershBJ. Contemporarymanagementofangina:partII.Medicalmanagementofchronicstableangina. AmFamPhysician. 2000;61(1):129-138. PubMed GoogleScholar RihalCS,RacoDL,GershBJ,YusefS. Indicationsforcoronaryarterybypasssurgeryandpercutaneouscoronaryinterventioninchronicstableangina:reviewoftheevidenceandmethodologicalconsiderations. Circulation. 2003;108(20):2439-2445. ViewArticle PubMed GoogleScholar EagleKA,GuytonRA,DavidoffR,etal. ACC/AHAguidelinesforcoronaryarterybypassgraftsurgery:executivesummaryandrecommendations:areportoftheAmericanCollegeofCardiology/AmericanHeartAssociationTaskForceonPracticeGuidelines(CommitteetoRevisethe1991GuidelinesforCoronaryArteryBypassGraftSurgery). Circulation. 1999;100(13):1464-1480. ViewArticle PubMed GoogleScholar TheBypassAngioplastyRevascularizationInvestigationInvestigators.Comparisonofcoronarybypasssurgerywithangioplastyinpatientswithmultivesseldisease. NewEngJMed.1996;335:217-225. ViewArticle GoogleScholar PocockSJ,HendersonRA,RickardsAF,etal. Meta-analysisofrandomizedtrialscomparingcoronaryangioplastywithbypasssurgery. Lancet. 1995;346(8984):1184-1189. ViewArticle GoogleScholar HoffmanSN,TenBrookJA,WolfMP,PaukerSG,SalemDN,WongJB. Ameta-analysisofrandomizedcontrolledtrialscomparingcoronaryarterybypassgraftwithpercutaneoustransluminalcoronaryangioplasty:onetoeightyearoutcomes. JAmCollCardiol. 2003;41(8):1293-1304. ViewArticle PubMed GoogleScholar AuthorInformation JenniferReenan,MDisaseniorresearchassociateintheAMAEthicsStandardsGroup. GotArt? Shareyourvisualsinourgallery. Submit EthicsEssayContest Winningessayistisawardeda$5000prize. 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