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Impulse Conduction MODULEMODULE 11 RhythmRhythm BasicsBasics ModuleModule 1:1: RhythmRhythm BBaasicssics OverviewOverview •• TheThe ConductionConduction SystemSystem –– ImpulseImpulse FormationFormation –– ImpulseImpulse ConductionConduction –– PropertiesProperties ofof CardiacCardiac FunctionFunction –– 55 PhasesPhases ofof ActionAction PotentialPotential •• RhythmRhythm DisordersDisorders –– MechanisMechanismsms –– ArrhythmArrhythmiaia RecognitionRecognition •• CausesCauses ofof RhythmRhythm DisordersDisorders ModuleModule 1:1: RhythmRhythm BBaasicssics ObjectivesObjectives •• IdentifyIdentify thethe componentscomponents thatthat makemake upup thethe electricalelectrical pathwaypathway knownknown asas thethe conductionconduction systemsystem •• StateState thethe 55 phasesphases ofof actionaction potentialpotential •• DescribeDescribe thethe mechanismsmechanisms causingcausing rhythmrhythm disordersdisorders •• IdIdentifyentify rhythmrhythm ddiisorderssorders onon anan EKGEKG THETHE CONDUCTIONCONDUCTION SYSTEMSYSTEM HeartHeart BeBeatat AnatomyAnatomy SINUS NODE • The Heart’s ‘Natural Pacemaker’ Sinus Node (SA Node) - 60-100 BPM at rest HeartHeart BeBeatat AnatomyAnatomy AV NODE • Receives impulse from Sinus Node SA Node (SA Node) • Delivers impulse to the His- Purkinje System Atrioventricular Node (AV Node) • 40-60 BPM if SA Node fails to deliver an impulse HeartHeart BeBeatat AnatomyAnatomy BUNDLE OF HIS •Begins conduction to Sinus Node the Ventricles (SA Node) • AV Junctional Tissue: 40-60 BPM Atrioventricular Node (AV Node) Bundle of His HeartHeart BeBeatat AnatomyAnatomy THE PURKINJE NETWORK • Bundle Branches Sinus Node (SA Node) • Purkinje Fibers • Moves the impulse through the ventricles for contraction Atrioventricular Node (AV Node) • Provides ‘Escape Rhythm’: 20-40 BPM Bundle of His Bundle Branches Purkinje Fibers NormalNormal SinusSinus RhythmRhythm *Animation Click heart to view animation ImpulseImpulse FormationFormation InIn SASA NodeNode AtrialAtrial DepolarizationDepolarization DelayDelay AtAt AVAV NodeNode ConductConductiionon ThroughThrough BundleBundle BranchesBranches ConductConductiionon ThroughThrough PurkinjePurkinje FiberFiberss VentricularVentricular DepDepoolarizationlarization PlateauPlateau PhasePhase ofof RepolarizationRepolarization FinalFinal RapidRapid (Phase(Phase 3)3) RepolarizationRepolarization NormalNormal EKGEKG ActivationActivation ReadingReading EKGsEKGs IntervalsIntervals andand TimingTiming NormalNormal RRaannggeses inin MiMillisecolliseconds:nds: •• PRPR IntervalInterval 120120 –– 220000 mmss •• QRSQRS ComplexComplex 6060 –– 110000 msms •• QTQT IntervalInterval 363600 –– 444040 mmss QuesQuestion?tion? WherWheree doesdoes thethe SASA NodeNode getget itsits energy?energy? AutomaticAutomaticiityty CardiacCardiac CCeellslls havehave AUTOMAUTOMATICIATICITTY!Y! AutomaticAutomaticiityty CaCardiacrdiac CellsCells •• SpontaneouslySpontaneously depolarizedepolarize •• GenerallyGenerally presentpresent inin:: •• UpperUpper (SA(SA Node)Node) -- 660-0-101000 BPMBPM •• MiddleMiddle (AV(AV JJuunction)nction) -- 440-0-6060 BPMBPM •• LowerLower (Pur(Purkinjekinje Network)Network) -- 220–0–4040 BPMBPM AutomaticAutomaticiityty OnceOnce aa papacemakercemaker cellcell initiainitiatestes anan impulse,impulse, itsits neighbneighboringoring cellscells followfollow suitsuit –– llikeike dominos!dominos! QuesQuestion?tion? WhatWhat TriggersTriggers thethe FirstFirst Cell?Cell? ActionAction PotentialPotential ofof aa CardiacCardiac CellCell 55 PhasesPhases ActionAction PotentialPotential ofof aa CardiacCardiac CellCell 55 PhasesPhases •• PhasePhase 00 –R–Raappiidd oorr uuppssttrrookkee depodepolarizatlarizatiioonn witwithh anan infinflluxux ofof sodiumsodium ionsions intointo thethe cellcell ActionAction PotentialPotential ofof aa CardiacCardiac CellCell 55 PhasesPhases •• PhasePhase 00 –R–Raappiidd uuppssttrrookkee depodepolarizatlarizatiioonn witwithh anan infinflluxux ofof sodiumsodium ionsions intointo thethe cellcell •• PhasePhase 11 –– EEarlyarly rapidrapid repolarizationrepolarization wwiithth transtransiientent outwoutwardard movemmovemeentnt ofof potassiumpotassium ionsions ActionAction PotentialPotential ofof aa CardiacCardiac CellCell 55 PhasesPhases •• PhasePhase 00 –R–Raappiidd uuppssttrrookkee depodepolarizatlarizatiioonn witwithh anan infinflluxux ofof sodiumsodium ionsions intointo thethe cellcell •• PhasePhase 11 –– EEarlyarly rapidrapid repolarizationrepolarization withwith transienttransient onwardonward movemmovemeentnt ofof potassiumpotassium ionsions •• PhasePhase 22 –– PPlateaulateau Phase:Phase: ContinuedContinued InfluxInflux ofof SodiumSodium && slowslow InfluxInflux ofof CalciumCalcium ActionAction PotentialPotential ofof aa CardiacCardiac CellCell 55 PhasesPhases •• PhasePhase 00 –R–Raappiidd uuppssttrrookkee depodepolarizatlarizatiioonn witwithh anan infinflluxux ofof sodiumsodium ionsions intointo thethe cellcell •• PhasePhase 11 –– EEarlyarly rapidrapid repolarizationrepolarization withwith transienttransient onwardonward movemmovemeentnt ofof potassiumpotassium ionsions •• PhasePhase 22 –– PPlateaulateau Phase:Phase: ContinuedContinued InfluxInflux ofof SodiumSodium && slowslow InfluxInflux ofof CalciumCalcium •• PhasePhase 33 –– RRepolarizationepolarization:: PPootastasssiiumum outflowoutflow ActionAction PotentialPotential ofof aa CardiacCardiac CellCell 55 PhasesPhases •• PhasePhase 00 –R–Raappiidd uuppssttrrookkee depodepolarizatlarizatiioonn witwithh anan infinflluxux ofof sodiumsodium ionsions intointo thethe cellcell •• PhasePhase 11 –– EEarlyarly rapidrapid repolarizationrepolarization withwith transienttransient onwardonward movemmovemeentnt ofof potassiumpotassium ionsions •• PhasePhase 22 –– PPlateaulateau Phase:Phase: ContinuedContinued InfluxInflux ofof SodiumSodium && slowslow InfluxInflux ofof CalciumCalcium •• PhasePhase 33 –– RRepolarizationepolarization:: PPootastasssiiumum outflowoutflow •• PhasePhase 44 –– RRestingesting PhasePhase ActionAction PotentialPotential ofof aa CardiacCardiac CellCell RefractoryRefractory PeriodsPeriods •• ERPERP -- EEffectffectiveive RefraRefracctorytory PeriodPeriod –Phases–Phases 0,0, 1,1, 22 andand earlyearly PhasePhase 33 –A–A depolarizationdepolarization cannotcannot bebe initiainitiatedted byby anan impulseimpulse ofof anyany strengthstrength ActionAction PotentialPotential ofof aa CardiacCardiac CellCell RefractoryRefractory PeriodsPeriods •• RRPRRP -- RRelelatiativvee RefraRefracctorytory PeriodPeriod ––LLateate PhasePhase 33 andand earlyearly PhasePhase 44 ––AA strongstrong impulseimpulse cancan causecause dedepolapolarization,rization, possiblpossiblyy wiwithth ababerrancyerrancy ActionAction PotentialPotential ofof aa CardiacCardiac CellCell EffectiveEffective && RelativRelativee RefractoryRefractory PeriodsPeriods QuesQuestion?tion? NowNow thatthat wewe understandunderstand impulseimpulse formationformation andand normalnormal heartheart function,function, let’slet’s thinthink…k… WhatWhat cancan possiblypossibly gogo wrongwrong?? RHYTHMRHYTHM DISORDERSDISORDERS RhythmRhythm DisordersDisorders 22 CaCategoritegorieses ofof RhytRhythmhm DisordersDisorders ImpulseImpulse FormationFormation DisordersDisorders ofof ImpulseImpulse ConductioConductionn RhythmRhythm DisordersDisorders UnderlyingUnderlying MechanismsMechanisms ImpulseImpulse FormationFormation •• AbAbnornormmalal AutomaticityAutomaticity ImpulseImpulse ConductioConductionn MechanismsMechanisms ofof RhyRhytthmhm DisordersDisorders AbnormalAbnormal AutomaticiAutomaticityty AbnormallyAbnormally SlowSlow == BradycardiaBradycardia •• FFailureailure duedue toto disdiseaseease ExcessivelyExcessively RapidRapid == TachycardiaTachycardia •• DDueue toto sympatheticsympathetic nervousnervous systemsystem MechanismsMechanisms ofof RhyRhytthmhm DisordersDisorders ImpulseImpulse FormationFormation •• AbAbnornormmalal AutomaticityAutomaticity •• TriggeredTriggered ActivitActivityy ImpulseImpulse ConductioConductionn MechanismsMechanisms ofof RhyRhytthmhm DisordersDisorders TriggeredTriggered ActivityActivity •• AAfterpotentialsfterpotentials occurrioccurringng inin PhasePhase 33 (early)(early) oror 44 (late)(late) ofof actionaction potentialpotential •• CCanan triggertrigger arrhythmiasarrhythmias MechanismsMechanisms ofof RhyRhytthmhm DisordersDisorders TriggeredTriggered ActivityActivity EarlyEarly AfteAfterdepolarizationrdepolarization LateLate AfterAfterddepolariepolarizzationation •• PotentiPotentiaall CaCauses:uses: •• PotentiPotentiaall CaCauses:uses: -- LLooww ppotassiumotassium bloodblood levelslevels –– PrematurePremature beatsbeats -- SSloloww heartheart raratete –– IncreasedIncreased calciumcalcium bloodblood -- DDrugrug toxictoxicityity (ex.(ex.
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