USMLE题库Cardiology(二)21-31

Cardiology2题库Q21Autopsyofa56-year-oldCaucasianmalewhodiedinamotorvehicleaccidentshowsincreasedthicknessoftheleftventricular(LV)wallanddecreasedLVcavitysize.Thestructuralchangesobservedinthispatient'sheartaremostlikelyassociatedwith:A.RecentmyocardialinfarctionB.MitralinsufficiencyC.AtrialseptaldefectD.HemochromatosisE.LongstandinghypertensionF.Wolff-Parkinson-WhitesyndromeG.NormalagingA21Correctanswer:FThechangesinthispatient'sLVareconsistentwithconcentrichypertrophyduetohypertensiveheartdisease.Concentrichypertrophyuniformlythickenstheventricularwallwhiletheouterdimensionsoftheventricleremainalmostunchanged,thusresultinginanarrowedventricularcavitysize.Concentrichypertrophyresultsfromchronicelevationoftheventricularpressureduringsystole(pressureoverload),asistypicallyseeninhypertensionduetotheincreasedLVafterload.(ChoiceA)Theventricularremodelingthatoccursafteranacutemyocardialinfarctioninvolvesexpansion,thinning,andfibroushealingoftheinfarctedzoneofmyocardium.Atthesametime,regionaldysfunctionoftheinfarctcausesvolumeoverloadfortheremainingviablemyocardium.Tocompensateforthelossofcontractilefunctionoftheinfarctedregion,thereishypertrophyoftheremainingmyocardium.Thenetresultisusuallydilatedventricularhypertrophy,withenlargementoftheLVcavity.(ChoiceB)MitralinsufficiencytendstoincreasetheLVend-diastolicvolume,causingLVdilatation.Additionally,becausetheLVneedstopumpoutbothforwardflowthroughtheaorticvalveandregurgitantflowthroughthemitralvalveduringsystole,thereisLVhypertrophyaswell.Thus,thenetstructuralconsequenceofmitralinsufficiencyisdilated/eftventricularhypertrophy.AlthoughtheLVmassisincreased,LVwallthicknessmaybeincreased,unchanged,orevendecreaseddependinguponthedegreeofLVdilatation.(ChoiceC)Anatrialseptaldefectcausesashuntingofbloodflowfromtheleftatriumtotherightatrium.Pulmonarybloodflowmaybeincreasedbytwotofourtimesthenormalvalue.Theresultisavolumeoverloadoftherightventricle,producingright-sideddilatedventricularhypertrophy.(ChoiceD)Hemochromatosiscanresultintheaccumulationofironinthemyocardiumashemosiderin.Adilatedcardiomyopathy,withincreasedLVcavitysize,isusuallytheendresult.Patientspresentwithsignsandsymptomsofcongestiveheartfailure.(ChoiceF)Wolff-Parkinson-Whitesyndromeisanelectrophysiologicalabnormalityofatrioventricularcardiacconduction.Thesepatientshaveaccessorypathways,whichdirectlyconnecttheatriaandventriclesandbypasstheAVnode.Thisresultsinpre-excitationandarrhythmias.Therearenotusuallygrossmorphologicalchangestotheleftventricleinthesepatients.(ChoiceG)AlthoughagingisassociatedwithadecreaseinLVchambersize,thisispredominantlyashorteningintheapex-to-basedimensionaccompaniedbyaleftwardbowingofthelowerinterventricularseptum(sigmoidseptum).Moreover,structuralcardiacchangesduetoagingaregenerallynotprominentbeforetheageof65.Q22A35-year-oldpreviouslyhealthymanisbroughttotheemergencydepartmentafterbeinginvolvedinamotorvehicleaccident.Hehassignificantbluntchestandheadtrauma.Shortlyafterhearrives,hisbloodpressuredropssuddenlyandhebeginsexperiencingrespiratorydistress.Onphysicalexamination,thepatientistachycardicandtachypneic.Hislungsarecleartoauscultationwithvesicularbreathsoundsheardbilaterally.Hehasjugularvenousdistention,andhissystolicbloodpressurefalls15mmHgwithinspiration.Whichofthefollowingisthemostlikelycauseofthispatient'sdeterioration?A.TensionpneumothoraxB..EpiduralhematomaC.HemothoraxD.AorticruptureE.CardiactamponadeA22Correctanswer:EThispatienthaspulsusparadoxus(afallinsystolicbloodpressure10mmHgoninspiration),jugularvenousdistention,andtachycardia.Basedonhishistoryandphysicalexaminationfindings,cardiactamponadeisthemostlikelydiagnosis.Cardiactamponadeshouldbesuspectedinanypatientwhohasthecharacteristictriadofmuffledheartsounds,jugularvenousdistention,andhypotension.Duringinspiration,thepressureinthepleuralspaceandlunginterstitiumdecreases,increasingpulmonaryvascularcapacitance.Thiscausesafallinvenousinflowtotheleftheart,resultingindecreasedleftventricularstrokevolumeandadropinsystolicbloodpressure(normally10mmHg).Theinspiratorydropinsystolicbloodpressureisexacerbatedincardiactamponadeduetoextrinsiccompressionoftheventricles.Thisexternalcompressionactstoequalizeleftandrightventriculardiastolicpressures,allowingtheintraventricularseptumtobulgeintotheleftventricleasaresultoftheinspiratoryincreaseinrightventricularfilling.Thisfurtherreducesleftventricularstrokevolume,leadingtoadropinsystolicbloodpressure10mmHg.Pulsusparadoxuscanalsooccurinotherconditions,includingconstrictivepericarditis,chronicobstructivepulmonarydisease,asthma,andpulmonaryembolism.(ChoiceA)Tensionpneumothoraxcancausehypotension,tachycardia,tachypnea,andjugularvenousdistension.Itcanresultfrombluntorpenetratingchesttraumathatinjuresthevisceralpleuraortracheobronchialtree.However,tensionpneumothoraxwouldcauseabsentbreathsoundsandhyperresonancetopercussionontheaffectedside.(ChoiceB)AnepiduralhematomamayinitiallycausehypertensionandbradycardiaduetoaCushing'sresponsetoincreasedintracranialpressure.Ifanepiduralhematomaprogressestoca