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Cardiac Arrhythmias II: Tachyarrhythmias. Supraventricular Tachycardias (Supraventricular - a rhythm process in which the ventricles are activated from

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Text of Cardiac Arrhythmias II: Tachyarrhythmias. Supraventricular Tachycardias (Supraventricular - a rhythm...

  • Cardiac Arrhythmias II: Tachyarrhythmias

  • Supraventricular Tachycardias(Supraventricular - a rhythm process in which the ventricles are activated from the atria or AV node/His bundle region)

  • Supraventricular Tachycardia (SVT) Terminology QRS typically narrow (in absence of bundle branch block); thus, also termed narrow QRS tachycardia Usually paroxysmal, i.e, starting and stopping abruptly; in which case, called PSVTParoxysmal Atrial Tachycardia (PAT) - the older term for PSVT - is misleading and should be abandoned

  • AV Junctional Reentrant Tachycardias(typically incorporate AV nodal tissue)

  • UnidirectionalBlockRecovery of Excitability & ReentryBidirectionalConductionMechanism of Reentry

  • AV Nodal Reentrant Tachycardia

  • AV Nodal Reentrant Tachycardia CircuitF = fast AV nodal pathwayS = slow AV nodal pathway(His Bundle)During sinus rhythm, impulses conduct preferentiallyvia the fast pathway

  • Initiation of AV Nodal Reentrant Tachycardia PAC = premature atrial complex (beat)PACPAC

  • Sustainment of AV Nodal Reentrant TachycardiaRate 150-250beats per minP waves generatedretrogradely(AV node atria) andfall within orat tail of QRS

  • PPPPSustained AV Nodal Reentrant TachycardiaNote fixed, short RP interval mimicking r deflection of QRS V1

  • Orthodromic AV Reentrant TachycardiaAPAnterogadeconduction via normal pathwayRetrograde conductionvia accessorypathway (AP)

  • Initiation of Orthodromic AV ReentrantTachycardiaAVNVentriclesAtriaAPPAC = premature atrial complex (beat)PAC

  • Sustainment of Orthodromic AV Reciprocating TachycardiaAtriaAPAVNVentriclesRetrograde Ps fall in the ST segmentwith fixed, short RPRate 150-250beats per min

  • Accessory Pathway with Ventricular Preexcitation(Wolff-Parkinson-White Syndrome) Fusion activation of the ventriclesAPPR < .12 sQRS .12 sSinusbeatHybrid QRS shape

  • Varying Degrees of Ventricular Preexcitation

  • Intermittent Accessory Pathway ConductionNormalConductionV PreexV PreexNote all-or-none nature of AP conduction

  • Orthodromic AV Reentrant TachycardiaNSR with V PreexSVT:V Preex goneNote retrograde P wavesin the ST segment

  • Concealed Accessory PathwayNo Delta wave during NSR(but AP capable of retrogradeconduction)Sinusbeat

  • Summary of AV Junctional Reentrant TachycardiasReentrant circuit incorporates AV nodal tissueP waves generated retrogradely over a fast pathwayShort, fixed RP interval

  • Clinical Significance of AV Junctional Reentrant TachycardiasRarely life-threateningHowever, may produce serious symptoms (dizziness or syncope [fainting])Can be very disruptive to quality of lifeInvolvement of an accessory pathway can carry extra risks

  • Atrial Tachyarrhythmias

  • Sinus Tachycardia (100 to 180+ beats/min) P waves oriented normally PR usually shorter than at rest

  • Causes of Sinus TachycardiaHypovolemia ( blood loss, dehydration)FeverRespiratory distressHeart failureHyperthyroidismCertain drugs (e.g., bronchodilators)Physiologic states (exercise, excitement, etc)

  • V5PPPPPTiming of Expected PPremature Atrial Complex (PAC)Non-Compensatory Pause

  • Premature Atrial Complex (PAC): Alternative TerminologyPremature atrial contraction Atrial extrasystoleAtrial premature beatAtrial ectopic beat Atrial premature depolarization

  • PACs: Bigeminal PatternPPPPPP Note deformation of T wave by the PAC Regularly Irregular Rhythm

  • PACs with Conduction Delay/BlockPhysiologic AV BlockPhysiologicAV Delay Recovered AV ConductionPPPPPP

  • PAC with Aberrant Conduction(Physiologic Delay in the His Purkinje System)V1PPPPRBBB

  • V1PACs with Aberrant Conduction(Physiologic RBBB and LBBB)RBBBLBBBNormalconduction

  • PACs with Physiologic LBBB and His-Purkinje System BlockV1Non-conductedPAC

  • Non-Conducted PAC PPPPV5V1Note deformation of T wave by the PAC

  • Bigeminal/Blocked PACs Mimicking Sinus BradycardiaV1Only the 4th bigeminal PAC conducts

  • Clinical Significance PACsCommon in the general populationMay be associated with heart diseaseCan be a precursor to atrial tachyarrhythmias

  • RP intervals can be variable RP often > PR (Example slower than more common rate mof 150-250 beats per min)

    Atrial TachycardiaV1 Differs fromAV nodal or AV reentrantSVT

  • Clinical Significance of Atrial TachycardiaSimilar to sequela of AV junctional reentrant tachycardiasMust be differentiated from them diagnostically

  • Atrial Flutter (Typical, Counterclockwise)Reentrant mechanism

  • IIV1 Atrial Flutter4:12:1Classicinverted sawtoothflutter wavesat 300 min-1 (best seen inII, III and AVF)Note variableventricularresponse

  • Atrial Flutter2:1Conduction(common)2:1 & 3:2Conduction1:1Conduction(rare but dangerous)V. rate 140-160beats/min

  • Atrial FibrillationFocal firingormultiplewaveletsChaotic, rapidatrial rate at400-600beats per min

  • V5Atrial Fibrillation Rapid, undulating baseline (best seen in V1) Most impulses block in AV node Erratic conductionV1

  • Atrial Fibrillation: Characteristic Irregularly Irregular Ventricular ResponseII

  • Atrial Fibrillation with Rapid Ventricular ResponseIIIrregularity may be subtle

  • Atrial Fibrillation: Autonomic Modulation of Ventricular Response BaselineImmediately after exercise

  • Clinical Significance of Atrial Flutter and FibrillationCauses Usually occur in setting of heart disease; but sometimes see lone atrial fibrillationHyperthyroidism (atrial fibrillation)May acutely precipitate myocardial ischemia or heart failureChronic uncontolled rates may induce cardiomyopathy and heart failureBoth can predispose to thromboembolic stroke, etc

  • Varying Degrees of Ventricular Preexcitation

  • Atrial Fibrillation with Rapid Conduction Via Accessory Pathway

  • Atrial Fibrillation with Third Degree AV BlockV1V5Regular ventricular rate reflects dissociated slow junctional escape rhythm

  • Regular Narrow QRS Tachycardias

  • Differential Diagnosis of Regular Narrow QRS (Supraventricular) Tachycardia Reentrant SVT incorporating AV nodal tissueAV nodal reentrant tachycardiaOrthodromic AV reentrant tachycardiaSVT mechanism confined to the atriaSinus tachycardiaAtrial flutterOther regular atrial tachycardiasShort-RP favors AV node-dependent reentrant SVT

  • Determining AV Nodal Participation in SVT by Transiently Depressing AV Nodal Conduction Vagotonic ManeuversCarotid sinus massageValsalva maneuver (bearing down)Facial ice pack (diving reflex; for kids)Adenosine (6-12 mg I.V.)If SVT breaks, a reentrant mechanism involving the AV node is likelyIf atrial rate unchanged, but ventricular rate slows (#Ps > #QRSs), SVT is atrial in origin

  • SVT Responses to AV Nodal Depressant ManeuversSVT terminationAV nodal reentrant tachycardiaOrthodromic AV reentrant tachycardiaNo SVT termination (despite maximal attempts)Sinus tachycardiaAtrial flutter or fibrillationMost atrial tachycardias (a minority are adenosine-sensitive)

  • Carotid Sinus MassageStimulation of carotid sinus triggers baroreceptorreflex and increased vagaltone, affectingSA and AV nodes

  • Termination of SVT by Vagotonic Maneuver (Carotid Sinus Massage)

  • SVTCarotid Sinus Massage

  • SVTAdenosine 6 mgPPPP

  • Ventricular Tachyarrhythmias

  • Premature Ventricular Complex (PVC): Alternative TerminologyPremature ventricular contraction Ventricular extrasystoleVentricular premature beatVentricular ectopic beat Ventricular premature depolarization

  • Premature Ventricular Complex (PVC)Compensatory Pause

  • PVCs: Bigeminal PatternRegularly Irregular Rhythm

  • Ectopic ventricular activation Normal ventricular activationFusionbeat Accelerated Idioventricular Rhythm (> Ventricular Escape Rate, but < 100 bpm)Sinus acceleration

  • SANodeVentricular FocusATRIA AND VENTRICLESACT INDEPENDENTLYAV Dissociation

  • V1Ventricular Tachycardia (VT) Rates range from 100-250 beats/min Non-sustained or sustained P waves often dissociated (as seen here)

  • Ladder Diagram of AV Dissociation During Ventricular Tachycardia Slower atrial rate Faster ventricular rate Impulses invade the AV node retrogradely and anterogradely,creating physiologic interference and block. Under the right conditions, some anterograde impulses may slip through.This phenomenon is not equivalent to third degree AV block

  • Ladder Diagram of AV Dissociation During Third Degree AV BlockFaster atrial rateSlower ventricular (escape) rhythmNote that impulses block anterogradely and retrogradelywithin the AV conduction system

  • Monomorphic VT

  • V1Polymorphic VT

  • Causes of PVCs and VTPVCs are fairly common in normals but are also seen in the setting of heart diseaseMonomorphic VT often implies heart disease, but can sometimes be seen in structurally normal heartsPolymorphic VT can result from myoardial ischemia or conditions that prolong ventricular repolarizationElectrolyte derangements, hypoxemia and drug toxicity can cause PVCs and VT

  • MI Scar-Related Sustained Monomorphic VT Circuit

  • Torsade de Pointes(Polymorphic VT Associated with Prolonged Repolarization)

  • Clinical Significance of PVCs and VTCan be a tip-off to underlying cardiac, respiratory or metabolic disorder VT may (but need not invariably) lead to hemodynamic collapse or more life-threatening ventricular tachyarrhythmias, increasing the risk of cardiac arrest

  • Ventricular Flutter VT > 250 beats/min, without clear isoelectric line Note sine wave-like appearance

  • Ventricular Fibrillation (VF) Totally chaotic rapid ventricular rhythm Often precipitated by VT Fatal unless promptly terminated (DC shock)

  • Sustained VT: Degeneration to VF

  • Atrial Fibrillation with Rapid Conduction Via Accessory Pathway: Degeneration to VF

  • Diagnosing Regular Wide QRS Tachycardia

  • Regular Wide QRS Tachycardia: VT or SVT with Aberrant Conduction?V1

  • Sustained Aberrant ConductionV1

  • Clinical Clues to Basis for Regular Wide QRS TachycardiaREMEMBER: VT does not invariably cause hemodynamic collapse; patients may be conscious and stable History of heart disease, especially prior myocardial infarction, suggests VTOccurrence in a young patient with no known heart disease suggests SVT12-lead EKG (if patient stable) should be obtained

  • Regular Wide QRS Tachycardia: VT or SVT with Aberrant Conduction?

  • More R-Waves Than P-Waves Implies VT!II

  • Artifact Mimicking Ventricular TachycardiaArtifact precedesVTQRS complexes march throughthe pseudo-tachyarrhythmia