Conduction Conduction AbnormalitiesAbnormalities

Michael Grushko, MDMichael Grushko, MD

Arrhythmia and ElectrophysiologyArrhythmia and Electrophysiology

Montefiore Medical CenterMontefiore Medical Center

Albert Einstein College of MedicineAlbert Einstein College of Medicine

Overview of Conduction Overview of Conduction AbnormalitiesAbnormalities

Sino Atrial Exit BlockSino Atrial Exit Block AV BlocksAV Blocks Bundle Branch BlockBundle Branch Block Fascicular BlockFascicular Block Indications For Permanent Pacemaker Indications For Permanent Pacemaker

ImplantationImplantation

Sino Atrial Exit BlockSino Atrial Exit Block• Implies that there is delay or failure of a normally Implies that there is delay or failure of a normally

generated sinus impulse to exit the nodal region.generated sinus impulse to exit the nodal region.

• First degree SA blockFirst degree SA block

• Second degree SA blockSecond degree SA block

1.Type 1 (Mobitz 1)1.Type 1 (Mobitz 1)2.Type 2 (Mobitz 2)2.Type 2 (Mobitz 2)

• Third degree SA blockThird degree SA block

First Degree Sino AtrialFirst Degree Sino Atrial Exit Block Exit Block

Implies that the conduction time Implies that the conduction time where each impulse leaving the node where each impulse leaving the node is prolongedis prolonged

This problem cannot be observed on This problem cannot be observed on surface EKGsurface EKG

Electro physiology study needed to Electro physiology study needed to measure the sino atrial conduction measure the sino atrial conduction time (SACT) time (SACT)

Second Degree Sino Second Degree Sino Atrial Atrial

Exit BlockExit Block Type I (SA Wenckebach) Type I (SA Wenckebach)

1. PP intervals gradually shorten until a pause 1. PP intervals gradually shorten until a pause occurs (i.e. the blocked sinus impulse fails to occurs (i.e. the blocked sinus impulse fails to reach the atria) reach the atria)

2. The pause duration is 2. The pause duration is less thanless than the two the two preceding PP intervals preceding PP intervals

3. The PP interval following the pause is 3. The PP interval following the pause is greater greater thanthan the PP interval just before the pause the PP interval just before the pause

Second DegreeSecond DegreeType II SA BlockType II SA Block

PP intervals fairly constant (unless PP intervals fairly constant (unless sinus arrhythmia present) until sinus arrhythmia present) until conduction failure occurs. conduction failure occurs.

The pause is approximately The pause is approximately twicetwice the basic PP interval the basic PP interval

Third Degree Or Complete Sino Third Degree Or Complete Sino Atrial Exit BlockAtrial Exit Block

Cannot be distinguished from a Cannot be distinguished from a prolonged sinus pause or arrestprolonged sinus pause or arrest

Can be identified from direct Can be identified from direct recording of sinus node pacemaker recording of sinus node pacemaker activity during an EP studyactivity during an EP study

AV BlockAV Block

AV Blocks: AV Blocks: Divided into incomplete and complete blockDivided into incomplete and complete block

Incomplete AV block includesIncomplete AV block includes

a. first-degree AV blocka. first-degree AV block

b. second degree AV blockb. second degree AV block

c. advanced AV blockc. advanced AV block

Complete AV block, also known as third degree AV Complete AV block, also known as third degree AV blockblock

Location of the BlockLocation of the Block

Proximal to, in, or distal to the His bundle Proximal to, in, or distal to the His bundle in thein theatrium or AV node atrium or AV node

All degrees of AV block may be All degrees of AV block may be intermittent or persistentintermittent or persistent

First Degree AV BlockFirst Degree AV Block PR interval is PR interval is

prolonged >0.20 prolonged >0.20 s (200 ms)s (200 ms)

no R-R interval no R-R interval changechange

Majority with site Majority with site of block in AV of block in AV nodenode

Etiologies:

•Normal

•Athletes

•High vagal tone

•Myocarditis/endocarditis

•Congenital heart disease

-ASD, PDA

•drugs

PR intervalPR interval

PR= PA + AH + HVPR= PA + AH + HV

P

AH

V

Second-Degree AV BlockSecond-Degree AV Block

There is intermittent failure of the There is intermittent failure of the supraventricular impulse to be conducted supraventricular impulse to be conducted to the ventriclesto the ventricles

Some of the P waves are not followed by a Some of the P waves are not followed by a QRS complex. The conduction ratio QRS complex. The conduction ratio (P/QRS ratio) may be set at 2:1, 3:1, 3:2, (P/QRS ratio) may be set at 2:1, 3:1, 3:2, 4:3, and so forth.4:3, and so forth.

Types Of Second-Degree AV BlockTypes Of Second-Degree AV Block

Type I also is called Wenckebach Type I also is called Wenckebach phenomenon or Mobitz type I (more phenomenon or Mobitz type I (more common and much more likely to occur at common and much more likely to occur at the AV nodal level)the AV nodal level)

Type II is also called Mobitz type II Type II is also called Mobitz type II

Type I Second-Degree AV Type I Second-Degree AV Block: Wenckebach Block: Wenckebach

PhenomenonPhenomenonECG findings ECG findings

1. Progressive lengthening of the PR 1. Progressive lengthening of the PR interval until a P wave is interval until a P wave is blockedblocked

2. P-P intervals remain constant2. P-P intervals remain constant

3. Progressive shortening of the RR 3. Progressive shortening of the RR interval until a P wave is blockedinterval until a P wave is blocked

4. RR interval containing the blocked P 4. RR interval containing the blocked P wave is shorter than the sum of two PP wave is shorter than the sum of two PP intervalsintervals

Second-Degree AV Block: Mobitz Second-Degree AV Block: Mobitz Type IIType II

ECG findings ECG findings 1. Intermittent blocked P waves1. Intermittent blocked P waves

2. PR intervals may be normal or prolonged, 2. PR intervals may be normal or prolonged, but they remain but they remain constantconstant

3. When the AV conduction ratio is 2:1, it is 3. When the AV conduction ratio is 2:1, it is often impossible to determine whether the often impossible to determine whether the second-degree AV block is type I or IIsecond-degree AV block is type I or II

4. A long rhythm strip may help4. A long rhythm strip may help

2:1 AVB2:1 AVB

2:1 AV block can possibly be from 2:1 AV block can possibly be from either second degree type I AV nodal either second degree type I AV nodal block (Wenckebach) or second block (Wenckebach) or second degree type II AV nodal block. This degree type II AV nodal block. This distinction is crucial since the distinction is crucial since the former is usually benign while the former is usually benign while the later usually requires implantation of later usually requires implantation of a permanent pacemaker.a permanent pacemaker.

2:1 AV Block2:1 AV Block

FeatureFeature Mobitz IMobitz I Mobitz IIMobitz II

QRS durationQRS duration NarrowNarrow WideWide

Maneuvers that Maneuvers that increase HR and AV increase HR and AV

conductionconduction

Block ImprovesBlock Improves Block worsensBlock worsens

That reduce HR and That reduce HR and AV conductionAV conduction

Block worsensBlock worsens Block improvesBlock improves

Develops during Develops during acute MIacute MI

Inferior MIInferior MI Anterior MIAnterior MI

OtherOther Mobitz I on another Mobitz I on another part of ECGpart of ECG

Hx of syncopeHx of syncope

2:1 AVB Dx Intervention2:1 AVB Dx Intervention Carotid sinus massage or adenosine: Carotid sinus massage or adenosine: This slows the sinus rate This slows the sinus rate

allowing the AV node more time to recover, thus reducing the allowing the AV node more time to recover, thus reducing the block from 2:1 to 3:2 and unmasking any progressing prolonging block from 2:1 to 3:2 and unmasking any progressing prolonging PR intervals that would indicate second degree type I AV nodal PR intervals that would indicate second degree type I AV nodal block.block.

Atropine administration: Atropine administration: This enhances AV nodal conduction This enhances AV nodal conduction and could eliminate second degree type I AV nodal block since it and could eliminate second degree type I AV nodal block since it is due to slowed AV nodal conduction) vs worsening AV block if is due to slowed AV nodal conduction) vs worsening AV block if etiology is infrahisianetiology is infrahisian

Exercise ECG testing Exercise ECG testing (enhances AV nodal conduction and could (enhances AV nodal conduction and could eliminate second degree type I AV nodal block since it is due to eliminate second degree type I AV nodal block since it is due to slowed AV nodal conduction)slowed AV nodal conduction)

High-Grade or Advanced High-Grade or Advanced AV BlockAV Block

When the AV conduction ratio is 3:1 or When the AV conduction ratio is 3:1 or higher,the rhythm is called advanced AV higher,the rhythm is called advanced AV blockedblocked

A comparison of the PR intervals of the A comparison of the PR intervals of the occasional captured complexes may occasional captured complexes may provide a clue provide a clue

If the PR interval varies and its duration is If the PR interval varies and its duration is inversely related to the interval between inversely related to the interval between the P wave and its preceding R wave (RP), the P wave and its preceding R wave (RP), type I block is likely type I block is likely

A constant PR interval in all captured A constant PR interval in all captured complexes suggests type II block complexes suggests type II block

Complete (Third-Degree) Complete (Third-Degree) AV BlockAV Block

There is complete failure of the There is complete failure of the supraventricular impulses to reach the supraventricular impulses to reach the ventriclesventricles

The atrial and ventricular activities are The atrial and ventricular activities are independent of each otherindependent of each other

ECG FindingsECG Findings

In patients with sinus rhythm and In patients with sinus rhythm and complete AV block, the PP and RR complete AV block, the PP and RR intervals are regular, but the P waves intervals are regular, but the P waves bear no constant relation to the QRS bear no constant relation to the QRS complexescomplexes

ie: A-V ie: A-V dissociation dissociation

Bundle Branch BlocksBundle Branch Blocks

BBBBBB

Bundle Branch BlockBundle Branch Block

• Left Bundle Branch BlockLeft Bundle Branch Block1. Complete LBBB1. Complete LBBB2. Incomplete LBBB2. Incomplete LBBB

• Rigt Bundle Branch BlockRigt Bundle Branch Block1. Complete RBBB1. Complete RBBB2. Incomplete RBBB2. Incomplete RBBB

Right Bundle Branch Right Bundle Branch BlockBlock

The diagnostic criteria includeThe diagnostic criteria include

1. QRS duration is >/- 120 ms1. QRS duration is >/- 120 ms

2. An rsr’,rsR’ or rSR’ pattern in lead 2. An rsr’,rsR’ or rSR’ pattern in lead V1 or V2 and occasionally a wide V1 or V2 and occasionally a wide and notched R wave.and notched R wave.

3. Reciprocal changes in V5,V6, I and 3. Reciprocal changes in V5,V6, I and AVL AVL

Causes of RBBBCauses of RBBB

1. After repair of the VSD 1. After repair of the VSD

2. After right ventriculotomy2. After right ventriculotomy

3. Right ventricular hypertrophy3. Right ventricular hypertrophy

4. Increase incidence of RBBB among 4. Increase incidence of RBBB among population at high altitudepopulation at high altitude

5. Ebstein’s anomaly5. Ebstein’s anomaly

6. Large ASD (secundum type) or AV cushion 6. Large ASD (secundum type) or AV cushion defectdefect

7. Brugada Syndrome7. Brugada Syndrome

8. Acute PE, chronic pulm disease8. Acute PE, chronic pulm disease

RBBB in the General RBBB in the General PopulationPopulation

The incidence increased with ageThe incidence increased with age

1.Below age 30 the incidence is 1.3 1.Below age 30 the incidence is 1.3 per 1000per 1000

2.Between 30 and 44 it ranges from 2.Between 30 and 44 it ranges from 2.0 to 2.9 per 10002.0 to 2.9 per 1000

Incomplete RBBBIncomplete RBBB

Criteria for incomplete RBBB are the Criteria for incomplete RBBB are the same as for complete RBBB except same as for complete RBBB except that the QRS duration is < 120 msthat the QRS duration is < 120 ms

Causes of Incomplete Causes of Incomplete RBBBRBBB

1. Atrial septal defect (RAD in secundum or 1. Atrial septal defect (RAD in secundum or sinus venosus type, LAD with ostium sinus venosus type, LAD with ostium primum type) primum type)

2. Ebstein’s anomaly2. Ebstein’s anomaly

3. Right ventricular dysplasia3. Right ventricular dysplasia

4. Congenital absence or atrophy of the 4. Congenital absence or atrophy of the bundle branchbundle branch

5. After CABG and in transplanted hearts5. After CABG and in transplanted hearts

6. Brugada Syndrome6. Brugada Syndrome

Left Bundle Branch BlockLeft Bundle Branch BlockElectrocardiographic Electrocardiographic

CriteriaCriteria1. The QRS duration is >/= 120 ms1. The QRS duration is >/= 120 ms

2. Leads V5,V6 and AVL show broad and 2. Leads V5,V6 and AVL show broad and notched or slurred R wavesnotched or slurred R waves

3. With the possible exception of lead AVL, 3. With the possible exception of lead AVL, the Q wave is absent in left-sided leadsthe Q wave is absent in left-sided leads

4. Reciprocal changes in V1 and V24. Reciprocal changes in V1 and V2

5. Left axis deviation may be present5. Left axis deviation may be present

Causes Of LBBBCauses Of LBBB

Hypertrophy, dilatation or fibrosis of the Hypertrophy, dilatation or fibrosis of the left ventricular myocardium left ventricular myocardium

Ischemic heart disease Ischemic heart disease

CardiomyopathiesCardiomyopathies

Advanced valvular heart diseaseAdvanced valvular heart disease Toxic, inflammatory changes Toxic, inflammatory changes

Hyperkalemia Hyperkalemia Digitalis toxicityDigitalis toxicity Degenerative disease of the conducting Degenerative disease of the conducting

system (Lenegre disease) system (Lenegre disease)

Prevalence Of LBBBPrevalence Of LBBB

At age 50 is 0.4%, and at age 80 it is 6.7%At age 50 is 0.4%, and at age 80 it is 6.7% In most subjects with LBBB, regional wall In most subjects with LBBB, regional wall

motion abnormalities (akinetic or motion abnormalities (akinetic or dyskinetic segments in the septum, dyskinetic segments in the septum, anterior wall or at the apex) are present anterior wall or at the apex) are present even in the absence of CAD or even in the absence of CAD or cardiomyopathycardiomyopathy

Incomplete Left Bundle Incomplete Left Bundle Branch BlockBranch Block

Criteria for incomplete LBBB includeCriteria for incomplete LBBB include

1. QRS duration > 100 ms but < 120 1. QRS duration > 100 ms but < 120 msms

2. Absence of a Q wave in leads V5,V6 2. Absence of a Q wave in leads V5,V6 and I and I

Fascicular BlocksFascicular Blocks

The left bundle branch divides into The left bundle branch divides into two fasciclestwo fascicles

1. Superior and anterior1. Superior and anterior

2. Inferior and posterior2. Inferior and posterior

Types Of Fascicular Types Of Fascicular BlockBlock

Left anterior fascicular blockLeft anterior fascicular block Left posterior fascicular blockLeft posterior fascicular block Bifascicular BlockBifascicular Block Trifascicular BlockTrifascicular Block

AxisAxis

Axis?Axis?

Left Anterior Fascicular Left Anterior Fascicular Block Block

Left axis deviation , usually -45 to -90 degrees Left axis deviation , usually -45 to -90 degrees

QRS duration usually <0.12s unless coexisting QRS duration usually <0.12s unless coexisting RBBB RBBB

Poor R wave progression in leads V1-V3 and Poor R wave progression in leads V1-V3 and deeper S waves in leads V5 and V6deeper S waves in leads V5 and V6

There is rS pattern in II, IIIThere is rS pattern in II, III

qR pattern in lead I and AVLqR pattern in lead I and AVL

R/o other causes of left axis deviationR/o other causes of left axis deviation

Causes of Left Anterior Causes of Left Anterior Fascicular BlockFascicular Block

1. Acute Myocardial Infarction1. Acute Myocardial Infarction

2. Hypertensive heart disease2. Hypertensive heart disease

3. Degenerative disease of the 3. Degenerative disease of the conducting systemconducting system

4. Myocardial fibrosis4. Myocardial fibrosis

Left Posterior Fascicular Left Posterior Fascicular BlockBlock

Diagnostic Criteria includeDiagnostic Criteria include

1. QRS duration <120 ms1. QRS duration <120 ms

2. 2. Right axis deviation (100 degree)Right axis deviation (100 degree)

3. qR pattern in inferior leads (II,III,AVF) 3. qR pattern in inferior leads (II,III,AVF) small q wavesmall q wave

4. rS patter in lead lead I and AVL4. rS patter in lead lead I and AVL

5. R/o other causes of right axis deviation5. R/o other causes of right axis deviation

LAD

RAD

Bifascicular Bundle Bifascicular Bundle Branch BlockBranch Block

RBBB with either left anterior or left RBBB with either left anterior or left posterior fascicular blockposterior fascicular block

Diagnostic criteriaDiagnostic criteria

1. Prolongation of the QRS duration to 0.12 1. Prolongation of the QRS duration to 0.12 second or longersecond or longer

2. rSR’ pattern in lead V12. rSR’ pattern in lead V1

3. Wide, slurred S wave in leads I, V5 and 3. Wide, slurred S wave in leads I, V5 and V6V6

4. Left axis or right axis deviation 4. Left axis or right axis deviation

Causes of Bifascicular Causes of Bifascicular BlockBlock

1. Coronary artery disease1. Coronary artery disease2. Degenerative disease of the conducting 2. Degenerative disease of the conducting

systemsystem3. Aortic stenosis3. Aortic stenosis4. Hypertensive heart disease 4. Hypertensive heart disease 5. Myocardial fibrosis5. Myocardial fibrosis6. Infiltrative process6. Infiltrative process7. Tetralogy of Fallot7. Tetralogy of Fallot8. After cardiac transplantation8. After cardiac transplantation

Trifascicular BlockTrifascicular Block

The combination of RBBB, LAFB and The combination of RBBB, LAFB and long PR interval long PR interval

Implies that conduction is delayed in Implies that conduction is delayed in the third fascicle the third fascicle

ExamplesExamples

SR with blocked APC’sSR with blocked APC’s

Complete Heart Block

Second Degree Type I AVB ie Wenkebach

Coronary AnatomyCoronary Anatomy

Coronary CirculationCoronary Circulation Sinus NodeSinus Node

-RCA 60%, LCX 40%-RCA 60%, LCX 40% AV NodeAV Node

-RCA 80%, LCX 10%, both 10%-RCA 80%, LCX 10%, both 10% Bundle of HisBundle of His

-AV nodal branch of RCA (small amount-AV nodal branch of RCA (small amountfrom septal perforators of LADfrom septal perforators of LAD

RBB- mainly septal perforators of LADRBB- mainly septal perforators of LAD LBB- LAF from the septal perforators of LAD LBB- LAF from the septal perforators of LAD

(very susceptible)(very susceptible) LPF- proximally from AVNodal/RCA and SP LPF- proximally from AVNodal/RCA and SP

of LAD, distally has dual blood supply from of LAD, distally has dual blood supply from the ant and post septal perforators. the ant and post septal perforators.

Sick Sinus Syndrome- Prolonged Sinus Node Recovery Time

Wenkebach with GAP phenomenon

Where is the likely level of block?

Indications For Indications For Implantation of Implantation of

Permanent Pacing in Permanent Pacing in Acquired AV BlockAcquired AV Block Class IClass I

1.Third-degree AV block associated with1.Third-degree AV block associated witha.Bradycardia with symptoms (C)a.Bradycardia with symptoms (C)b.Arrhythmias and other medical conditions that b.Arrhythmias and other medical conditions that

require drugs that result in symptomatic require drugs that result in symptomatic bradycardia(C)bradycardia(C)

c.Asystole>/-3.0 seconds or any escape c.Asystole>/-3.0 seconds or any escape rate<40bpm awake, symptom free Pt (B,C)rate<40bpm awake, symptom free Pt (B,C)

d.After catheter ablation of the AV junction (B,C) d.After catheter ablation of the AV junction (B,C) e.Neuromuscular diseases with AV block (Myotonic e.Neuromuscular diseases with AV block (Myotonic

muscular dystrophy)muscular dystrophy)2.Second-degree AV block with symptomatic 2.Second-degree AV block with symptomatic

bradycardiabradycardia

Class IIaClass IIa

Asymptomatic third-degree AV block Asymptomatic third-degree AV block with average awake ventricular rates of with average awake ventricular rates of 40 bpm or faster (B,C)40 bpm or faster (B,C)

Asymptomatic type II second-degree AV Asymptomatic type II second-degree AV block block (B)(B)

First-degree AV block with symptoms First-degree AV block with symptoms suggestive of pacemaker syndrome and suggestive of pacemaker syndrome and documented alleviation of symptoms documented alleviation of symptoms with temporary AV pacing with temporary AV pacing (B)(B)

Class IIbClass IIb

Marked first-degree AV block (>0.30 Marked first-degree AV block (>0.30 second) in patients with LV dysfunction second) in patients with LV dysfunction and symptoms of congestive heart and symptoms of congestive heart failure in whom a shorter AV interval failure in whom a shorter AV interval results in hemodynamic improvement, results in hemodynamic improvement, presumably by decreasing left atrial presumably by decreasing left atrial filling pressure filling pressure (C)(C)

Class IIIClass III

Asymptomatic first-degree AV block Asymptomatic first-degree AV block (B)(B)

Asymptomatic type I second-degree Asymptomatic type I second-degree AV block at the supra-His (AV node) AV block at the supra-His (AV node) level or not known to be intra- or level or not known to be intra- or infra-Hisian infra-Hisian (B, C)(B, C)

AV block expected to resolve and AV block expected to resolve and unlikely to recur (eg,drug toxicity, unlikely to recur (eg,drug toxicity, Lyme disease) Lyme disease) (B)(B)

Indications for Permanent Indications for Permanent Pacing in Chronic Bifascicular Pacing in Chronic Bifascicular

and Trifascicular Blockand Trifascicular Block1.Class I1.Class I Intermittent third-degree AV block. Intermittent third-degree AV block. (B)(B) Type II second-degree AV block. Type II second-degree AV block. (B)(B)2.Class IIa2.Class IIa Syncope not proved to be due to AV block when Syncope not proved to be due to AV block when

other likely causes have been excluded, other likely causes have been excluded, specifically ventricular tachycardia (VT). specifically ventricular tachycardia (VT). (B)(B)

3.Class III3.Class III Fascicular block without AV block or symptoms. Fascicular block without AV block or symptoms.

(B)(B) Fascicular block with first-degree AV block Fascicular block with first-degree AV block

without symptoms. without symptoms. (B)(B)

Indications for Permanent Indications for Permanent Pacing After The Acute Phase Pacing After The Acute Phase

Of Myocardial InfarctionOf Myocardial Infarction Class IClass I Persistent second-degree AV block with Persistent second-degree AV block with

bilateral bundle branch block or third-degree bilateral bundle branch block or third-degree AV block within or below the His-Purkinje AV block within or below the His-Purkinje system after AMI. system after AMI. (B)(B)

Transient advanced (second- or third-degree) Transient advanced (second- or third-degree) infranodal AV block with bundle branch infranodal AV block with bundle branch block. block. (B)(B)

Persistent and symptomatic second- or third-Persistent and symptomatic second- or third-degree AV block. degree AV block. (C)(C)

Indications Of Permanent Indications Of Permanent Pacing After the Acute Phase Pacing After the Acute Phase

Of Myocardial Infarction Of Myocardial Infarction (Continuation)(Continuation)

Class IIb Class IIb Persistent second- or third-degree AV block at the Persistent second- or third-degree AV block at the

AV node level. AV node level. (B)(B) Class III Class III

Transient AV block in the absence of intraventricular Transient AV block in the absence of intraventricular conduction defects. conduction defects. (B)(B)

Transient AV block in the presence of isolated left Transient AV block in the presence of isolated left anterior fascicular block. anterior fascicular block. (B)(B)

Acquired left anterior fascicular block in the absence Acquired left anterior fascicular block in the absence of AV block. of AV block. (B)(B)

Persistent first-degree AV block in the presence of Persistent first-degree AV block in the presence of bundle branch blockbundle branch block that is old or age that is old or age indeterminate. indeterminate. (B)(B)