USMLE题库Cardiology(一)21-30

Cardiology1题库Q21A56-year-oldmancomestothecardiologyclinicbecauseoffatigue,palpitations,andexertionaldyspneaoverthelastseveralweeks.Onphysicalexamination,hisheartrateisirregularandmeasures122beatsperminute,whilehisbloodpressureis110/70mmHg.Thepatientundergoesfurtherwork-up,includingECG,radiographicstudies,andlaboratorystudies.HisECGshowsatrialfibrillationandtrans-esophagealechocardiographyrevealsathrombusinadilatedleftatrium.Intheeventofaninterruptionofbloodflowsecondarytoarterialocclusion,whichofthefollowingorganswouldbeleastvulnerabletoinfarction?A.SpleenB.BrainC.KidneyD.LiverE.HeartA21Correctanswer:DInfarctsinanotherwisenormalliverarerarebecauseithasadualbloodsupply:theportalveinandhepaticartery.Shouldthehepaticarterybecomeoccluded,theportalvenoussupplyandretrogradearterialflowthroughaccessoryvessels(e.g.,fromtheinferiorphrenic,adrenal,intercostalarteries,etc.)istypicallysufficienttosustaintheliverparenchyma.Thenotableexceptioniswhenatransplantedliverundergoeshepaticarterythrombosis.Inthiscase,thelivercandevelopbiliarytreeinfarctionandorganfailurebecausethecollateralbloodsupplyisseveredduringtransplantation.(ChoiceA)Thespleenisrelativelyvulnerabletoinfarctionbecausetheperfusionviathesplenicarteryisend-arterial.Wedge-shaped,capsule-basedsplenicinfarctsoccurandareaknowncomplicationofsicklecellanemia,infectiveendocarditis,andcardiacmuralthrombosis.(ChoiceB)Irreversibledamageappearstooccurinthemostvulnerableofneuronsafterapproximately5minutesofcompleteischemia.(ChoiceC)Thekidney,similartothespleen,hasanend-arterialbloodsupply,andisgenerallyabletotoleratewarmischemiaforatleast30minutes.Longerperiodsofcompleteischemiaresultinimmediatefunctionalloss;laterecoveryofrenalfunctionisincompleteorabsent.(ChoiceE)Themyocardiumcanendurecompletearterialischemiafortwentyorthirtyminuteswithoutsevereconsequences.Brieferperiodsofischemiadonotresultinnecrosis,butrathermyocardialstunning.Coronaryarteryembolismisanuncommoncauseofmyocardialinfarction;nonetheless,itshouldbeconsideredinmyocardial-infarctedpatientswithatrialfibrillation,infectiveendocarditis,leftatrialorventricularthrombus,andinpatientsundergoingcardiaccatheterization.Q22Autopsyofan86-year-oldCaucasianmaleshowslocalizedamyloiddepositioninthecardiacatria.Nootherorgansareinvolved.Theamyloidismostlikelycomposedofwhichofthefollowingpolypeptidefragments?A.CalcitoninB.ProlactinC.AmylinD-(3-amyloidproteinE.ImmuneglobulinlightchainF.NatriureticpeptideA22Correctanswer:FLocalizedamyloidosisconfinedtothecardiacatria(isolatedatrialamyloidosis,orIAA)isduetodepositionofabnormallyfolded〇-pleatedsheetconformation)atrialnatriureticpeptide-derivedproteins.TheincidenceofIAAincreaseswithage,reaching90%intheninthdecade.Thisisaformofsenilecardiacamyloidosiswhichmayincreasetheriskofatrialfibrillation.(ChoiceA)Depositionofabnormallyfoldedcalcitonin-derivedpeptidesisresponsibleforlocalizedamyloidosisofthethyroidglandinpatientswithmedullarycarcinomaofthethyroid.(ChoiceB)Depositionofabnormallyfoldedprolactin-derivedproteinsmayberesponsibleforlocalizedamyloidosisofthepituitarygland.(ChoiceC)Isletamyloidprotein(amylin)isusuallyfoundinpatientswithlocalizedpancreaticamyloidosis.Itisdetectedinthepancreaticisletsofmorethan90%ofpatientswithtype2diabetes.(ChoiceD)(3-amyloidproteinisthe4000DaltonpeptidefoundinthecoreofthecerebralplaquesofAlzheimerdisease,β-amyloidproteinisalsofoundinlocalizedamyloiddepositsinthewallsofcerebralbloodvesselsofAlzheimerpatientsaswellasinpatientswithcerebralamyloidangiopathy(CAA).(ChoiceE)Depositionofimmuneglobulinlightchains，especiallyλ-lightchainsandtheirfragments,isresponsibleforprimarysystemic(notlocalized)amyloidosis.PrimarysystemicamyloidosisarisesinassociationwithmonoclonalB-cellproliferations(e.gmultiplemyeloma)andcausessystemicamyloiddepositioninvolvingtheheart,aswellastheskin,tongue,gastrointestinaltract,kidney,andperipheralnerves.Immunoglobulinlightchainsofeithertheλortheκvariety(BenceJonesproteins)mayalsobefoundintheserumandurine.Q23A21-year-oldCaucasianmalepresentstotheemergencydepartmentfollowinganepisodeofsyncope.Thesyncopalepisodewasnotprovokedbyanyactivityorcircumstance,norwasitprecededbylightheadedness.Thepatienthasnosignificantpastmedicalhistoryandheisnottakinganymedications.AnECGobtainedintheERrevealsQT-intervalprolongationbutisotherwiseunremarkable.Assumingthisisaninheritedcondition,therelevantmutationmostlikelyaffectswhichofthefollowingstructures?A.CardiaccellcytoskeletonproteinsB.CardiaccellsarcomereproteinsC.MitochondrialenzymesofoxidativephosphorylationD.Calcium-bindingsarcoplasmicreticulumproteinE.MembranepotassiumchannelproteinsA23Correctanswer:EThispatient’ssudden-onsetsyncopalepisodesuggestsasuddencardiacarrhythmia.QTprolongationinanotherwisehealthyyoungindividualisusuallycongenital.ThemutationmostlikelytocauseQT-intervalprolongationcanbedeterminedbasedonanunderstandingofcardiacelectrophysiology.OnanECGtracing,theQTintervalbeginsatthestartoftheQRScomplexandendsattheendoftheTwave.Thus,theQT-intervalreflectsthecardiacmyocyteactionpotentialdurati