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MODULE 1Rhythm Basics

Module 1: Rhythm BasicsOverview The Conduction System––––Impulse FormationImpulse ConductionProperties of Cardiac Function5 Phases of Action Potential Rhythm Disorders––MechanismsArrhythmia Recognition Causes of Rhythm Disorders

Module 1: Rhythm BasicsObjectives Identify the components that make up theelectrical pathway known as the conductionsystem State the 5 phases of action potential Describe the mechanisms causing rhythmdisorders Identify rhythm disorders on an EKG

THE CONDUCTION SYSTEM

Heart Beat AnatomySINUS NODESinus Node(SA Node) The Heart’s ‘Natural Pacemaker’- 60-100 BPM at rest

Heart Beat AnatomyAV NODESinus Node(SA Node)AtrioventricularNode (AV Node) Receives impulse fromSA Node Delivers impulse to the HisPurkinje System 40-60 BPM if SA Node fails todeliver an impulse

Heart Beat AnatomyBUNDLE OF HISSinus Node(SA Node)AtrioventricularNode (AV Node)Bundle of His Begins conduction tothe Ventricles AV Junctional Tissue:40-60 BPM

Heart Beat AnatomyTHE PURKINJE NETWORKSinus Node(SA Node)AtrioventricularNode (AV Node)Bundle of HisBundle BranchesPurkinje Fibers Bundle Branches Purkinje Fibers Moves the impulse throughthe ventricles for contraction Provides ‘Escape Rhythm’:20-40 BPM

Normal Sinus Rhythm*AnimationClick heart toview animation

Impulse Formation In SA Node

Atrial Depolarization

Delay At AV Node

Conduction Through Bundle Branches

Conduction Through Purkinje Fibers

Ventricular Depolarization

Plateau Phase of Repolarization

Final Rapid (Phase 3) Repolarization

Normal EKG Activation

Reading EKGsIntervals and TimingNormal Rangesin Milliseconds: PRPR IntervalInterval 120120 –– 200200 msmsQRSQRS ComplexComplex 6060 –– 100100 msmsQTQT IntervalInterval 360360 –– 440440 msms

Question?Where does the SA Node get its energy?

AutomaticityCardiac Cells haveAUTOMATICITY!

AutomaticityCardiac Cells Spontaneously depolarize Generally present in: Upper (SA Node)- 60-100 BPM Middle (AV Junction)- 40-60 BPM Lower (Purkinje Network)- 20–40 BPM

AutomaticityOnce a pacemaker cell initiates an impulse,its neighboring cells follow suit – like dominos!

Question?What Triggers the First Cell?

Action Potential of a Cardiac Cell5 Phases

Action Potential of a Cardiac Cell5 Phases Phase 0–– RapidRapid oror upstrokeupstrokedepolarizationdepolarization withwith anan influxinfluxofof sodiumsodium ionsions intointo thethe cellcell

Action Potential of a Cardiac Cell5 Phases Phase 0–– RapidRapid upstrokeupstrokedepolarizationdepolarization withwith anan influxinfluxofof sodiumsodium ionsions intointo thethe cellcell Phase 1–– EarlyEarly rapidrapid repolarizationrepolarizationwithwith transienttransient outwardoutwardmovementmovement ofof potassiumpotassium ionsions

Action Potential of a Cardiac Cell5 Phases Phase 0–– RapidRapid upstrokeupstrokedepolarizationdepolarization withwith anan influxinfluxofof sodiumsodium ionsions intointo thethe cellcell Phase 1–– EarlyEarly rapidrapid repolarizationrepolarizationwithwith transienttransient onwardonwardmovementmovement ofof potassiumpotassium ionsions Phase 2–– PlateauPlateau Phase:Phase: ContinuedContinuedInfluxInflux ofof SodiumSodium && slowslowInfluxInflux ofof CalciumCalcium

Action Potential of a Cardiac Cell5 Phases Phase 0–– RapidRapid upstrokeupstrokedepolarizationdepolarization withwith anan influxinfluxofof sodiumsodium ionsions intointo thethe cellcell Phase 1–– EarlyEarly rapidrapid repolarizationrepolarizationwithwith transienttransient onwardonwardmovementmovement ofof potassiumpotassium ionsions Phase 2–– PlateauPlateau Phase:Phase: ContinuedContinuedInfluxInflux ofof SodiumSodium && slowslowInfluxInflux ofof CalciumCalcium Phase 3–– Repolarization:Repolarization:PotassiumPotassium outflowoutflow

Action Potential of a Cardiac Cell5 Phases Phase 0–– RapidRapid upstrokeupstrokedepolarizationdepolarization withwith anan influxinfluxofof sodiumsodium ionsions intointo thethe cellcell Phase 1–– EarlyEarly rapidrapid repolarizationrepolarizationwithwith transienttransient onwardonwardmovementmovement ofof potassiumpotassium ionsions Phase 2–– PlateauPlateau Phase:Phase: ContinuedContinuedInfluxInflux ofof SodiumSodium && slowslowInfluxInflux ofof CalciumCalcium Phase 3–– Repolarization:Repolarization:PotassiumPotassium outflowoutflow Phase 4–– RestingResting PhasePhase

Action Potential of a Cardiac CellRefractory Periods ERP - EffectiveRefractory Period–Phases 0, 1, 2 and earlyPhase 3–A depolarization cannotbe initiated by animpulse of any strength

Action Potential of a Cardiac CellRefractory Periods RRP - RelativeRefractory Period–Late Phase 3 and earlyPhase 4–A strong impulse cancause depolarization,possibly with aberrancy

Action Potential of a Cardiac CellEffective & Relative Refractory Periods

Question?Now that we understand impulse formationand normal heart function, let’s think What can possibly go wrong?

RHYTHM DISORDERS

Rhythm Disorders2 Categories of Rhythm DisordersDisorders ofImpulse FormationImpulse Conduction

Rhythm DisordersUnderlying MechanismsImpulse FormationImpulse Conduction AbnormalAbnormal AutomaticityAutomaticity

Mechanisms of Rhythm DisordersAbnormal AutomaticityAbnormally Slow Bradycardia Failure due to diseaseExcessively Rapid Tachycardia Due to sympathetic nervous system

Mechanisms of Rhythm DisordersImpulse Formation AbnormalAbnormal AutomaticityAutomaticity TriggeredTriggered ActivityActivityImpulse Conduction

Mechanisms of Rhythm DisordersTriggered Activity Afterpotentials occurring inPhase 3 (early) or 4 (late) ofaction potential Can trigger arrhythmias

Mechanisms of Rhythm DisordersTriggered ActivityEarly AfterdepolarizationLate Afterdepolarization Potential Causes: - Low potassium blood levels- Slow heart rate- Drug toxicity (ex. Quinidinecausing Torsades de Pointes)Potential Causes:– Premature beats– Increased calcium bloodlevels– Increased adrenalinelevels– Digitalis toxicity

Mechanisms of Rhythm DisordersUnderlying MechanismsImpulse Formation AbnormalAbnormal AutomaticityAutomaticity TriggeredTriggered ActivityActivityImpulse Conduction SlowSlow oror BlockedBlockedConductionConduction

Mechanisms of Rhythm Disorders*AnimationSlowed or Blocked Conduction ImpulseImpulse generatedgenerated normallynormally ImpulseImpulse slowedslowed oror blockedblocked asas itit makesmakes itsits waywaythroughthrough thethe conductionconduction systemsystem

Mechanisms of Rhythm DisordersUnderlying MechanismsImpulse Formation AbnormalAbnormal AutomaticityAutomaticity TriggeredTriggered ActivityActivityImpulse Conduction SlowSlow oror BlockedBlockedConductionConduction Reentry

Mechanisms of Rhythm DisordersConditions of ReentryReentry

Mechanisms of Rhythm DisordersReentrySubstrate Trigger Reentry

Mechanisms of Rhythm DisordersReentry

ReentryIdentifying Reentry Pace the heart at a rate faster than theknown intrinsic tachycardia rate Stop the pacing If the intrinsic rate resumes tachycardic,then reentry is identified

RHYTHM DISORDERSBradyarrhythmias

Bradyarrhythmia ClassificationsClassification Based on DisorderImpulse FormationDisordersBradycardiasImpulse ConductionDisorders

Bradyarrhythmia ClassificationsClassification Based on DisorderImpulse FormationDisordersImpulse ConductionDisorders SinusSinus ArrestArrest

Sinus Arrest*Animation Failure of sinus node discharge Absence of atrial depolarization Periods of asystole

Bradyarrhythmia ClassificationsClassification Based on DisorderImpulse FormationDisordersImpulse ConductionDisorders SinusSinus ArrestArrest SinusSinus BradycardiaBradycardia

Sinus Bradycardia Sinus Node emits energy very slowly

Bradyarrhythmia ClassificationsClassification Based on DisorderImpulse FormationDisordersImpulse ConductionDisorders SinusSinus ArrestArrest SinusSinus BradycardiaBradycardia Brady/TachyBrady/Tachy SyndromeSyndrome

Brady/Tachy Syndrome Intermittent episodes of slow andfast rates from the SA node or atria Brady 60 BPM Tachy 100 BPM

Bradyarrhythmia ClassificationsClassification Based on DisorderImpulse FormationDisorders SinusSinus ArrestArrest SinusSinus BradycardiaBradycardia Brady/TachyBrady/Tachy SyndromeSyndromeImpulse ConductionDisorders ExitExit BlockBlock

Exit Block Transient block of impulses from the SA node Identified by P-P interval relationship

Bradyarrhythmia ClassificationsClassification Based on DisorderImpulse FormationDisorders SinusSinus ArrestArrest SinusSinus BradycardiaBradycardia Brady/TachyBrady/Tachy SyndromeSyndromeImpulse ConductionDisorders ExitExit BlockBlock 11stst DegreeDegree AVAV BlockBlock

First-Degree AV Block PR interval 200 ms Delayed conduction through the AV Node- Example shows PR Interval 320 ms

Bradyarrhythmia ClassificationsClassification Based on DisorderImpulse FormationDisorders SinusSinus ArrestArrest SinusSinus BradycardiaBradycardia Brady/TachyBrady/Tachy SyndromeSyndromeImpulse ConductionDisorders ExitExit BlockBlock 11stst DegreeDegree AVAV BlockBlocknd Degree 22ndDegree AVAV BlockBlock

Second-Degree AV Block - Mobitz I*AnimationKnown as Wenckebach Block Progressive prolongation of the PR interval untilthere is failure to conduct and a ventricular beatis dropped

Second-Degree AV Block – Mobitz II Regularly dropped ventricular beats– Ex: 2:1 block (2 P-waves to 1 QRS complex)– Atrial rate 75 BPM– Ventricular rate 42 BPM

Bradyarrhythmia ClassificationsClassification Based on DisorderImpulse FormationDisorders SinusSinus ArrestArrest SinusSinus BradycardiaBradycardia Brady/TachyBrady/Tachy SyndromeSyndromeImpulse ConductionDisorders ExitExit BlockBlock 11stst DegreeDegree AVAV BlockBlocknd Degree 22ndDegree AVAV BlockBlockrd Degree 33rdDegree AVAV BlockBlock

Third-Degree AV Block*Animation No impulse conduction from the atria to theventricles– Ventricular rate 37 BPM– Atrial rate 130 BPM– PR interval variable

Bradyarrhythmia ClassificationsClassification Based on DisorderImpulse FormationDisorders SinusSinus ArrestArrest SinusSinus BradycardiaBradycardia Brady/TachyBrady/Tachy SyndromeSyndromeImpulse ConductionDisorders ExitExit BlockBlock 11stst DegreeDegree AVAV BlockBlocknd Degree 22ndDegree AVAV BlockBlockrd Degree 33rdDegree AVAV BlockBlock Bi/TrifascicularBi/Trifascicular BlockBlock

Bifascicular Block A complete or incomplete block in at least twoconduction system pathways below the AV Node Marked by a widened QRS

Bifascicular BlockRightRight bundlebundlebranchbranch blockblockandand leftleft anterioranteriorhemiblockhemiblockRightRight bundlebundlebranchbranch blockblock andandleftleft te leftleftbundlebundle branchbranchblockblock

Trifascicular Block Complete block in the right bundle branch, andComplete or incomplete block in both divisions of theleft bundle branch Identified by EP Study

Bradyarrhythmia ClassificationsSummaryImpulse ConductionDisordersImpulse FormationDisorders SinusSinus ArrestArrestSinusSinus BradycardiaBradycardiaBrady/TachyBrady/Tachy SyndromeSyndrome ExitExit BlockBlock11stst DegreeDegree AVAV BlockBlocknd Degree22ndDegree AVAV BlockBlock--MobitzMobitz II (Wenckebach(Wenckebach Block)Block)-Mobitz-Mobitz IIIIrd Degree 33rdDegree AVAV BlockBlock Bi/TrifascicularBi/Trifascicular BlockBlock

RHYTHM DISORDERSTachyarrhythmias

Terms Describing Tachycardias Paroxysmal– Ectopic focus, sudden onset, abrupt cessation Sustained––Duration of 30 secondsRequires intervention to terminate Non-Sustained– At least 6 beats or 30 seconds– Spontaneously terminates Recurrent––Occurs periodicallyPeriods of no tachycardia are longer thanperiods of tachycardia

Terms Describing Tachycardias Incessant– Long periods of tachy, short periods of NSR Monomorphic– Single focus– Complexes are similar with equal intervals Polymorphic– Multiple foci– Complexes appear different with varied intervals SVT (Supraventricular Tachycardia)– Originating from above the ventricles

Tachyarrhythmia ClassificationsClassification Based on DisorderImpulse FormationDisordersTachycardiasImpulse ConductionDisorders