This document provides an overview of various conduction disturbances, including sinoatrial exit block, AV blocks, bundle branch blocks, and fascicular blocks. It describes the electrocardiographic findings and clinical implications of first-, second-, and third-degree forms of each type of block. Causes such as ischemia, cardiomyopathy, and inherited conduction system diseases are discussed. The prevalence of different blocks increases with age. Bundle branch blocks may occur after surgery involving the right ventricle. Permanent pacemaker implantation is indicated for advanced forms of block.

1. Conduction DisturbancesConduction Disturbances
Waseem Jaffrani,MDWaseem Jaffrani,MD
Department of CardiologyDepartment of Cardiology
Tulane University School ofTulane University School of
MedicineMedicine

2. Overview of the PresentationOverview of the Presentation
 Sino Atrial Exit BlockSino Atrial Exit Block
 AV BlocksAV Blocks
 Bundle Branch BlockBundle Branch Block
 Fascicular BlockFascicular Block
 Indications For PermanentIndications For Permanent
Pacemaker ImplantationPacemaker Implantation

3. Sino Atrial Exit BlockSino Atrial Exit Block
• Implies that there is delay or failure of aImplies that there is delay or failure of a
normally generated sinus impulse to exitnormally generated sinus impulse to exit
the nodal region.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

4. First Degree Sino AtrialFirst Degree Sino Atrial
Exit BlockExit Block
 Implies that the conduction timeImplies that the conduction time
where each impulse leaving the nodewhere each impulse leaving the node
is prolongedis prolonged
 This problem cannot be observed onThis problem cannot be observed on
surface EKGsurface EKG
 Electro physiology study needed toElectro physiology study needed to
measure the sino atrial conductionmeasure the sino atrial conduction
timetime

5. Second Degree Sino AtrialSecond Degree Sino Atrial
Exit BlockExit Block
 Type I (SA Wenckebach)Type I (SA Wenckebach)
1.PP intervals gradually shorten until a pause1.PP intervals gradually shorten until a pause
occurs (i.e., the blocked sinus impulse fails tooccurs (i.e., the blocked sinus impulse fails to
reach the atria)reach the atria)
2.The pause duration is2.The pause duration is less thanless than the twothe two
preceding PP intervalspreceding PP intervals
3.The PP interval following the pause is3.The PP interval following the pause is greatergreater
thanthan the PP interval just before the pausethe PP interval just before the pause

7. Second DegreeSecond Degree
Type II SA BlockType II SA Block
 PP intervals fairly constant (unlessPP intervals fairly constant (unless
sinus arrhythmia present) untilsinus arrhythmia present) until
conduction failure occurs.conduction failure occurs.
 The pause is approximatelyThe pause is approximately twicetwice thethe
basic PP intervalbasic PP interval

9. Third Degree Or Complete SinoThird Degree Or Complete Sino
Atrial Exit BlockAtrial Exit Block
 Cannot be distinguished from aCannot be distinguished from a
prolonged sinus pause or arrestprolonged sinus pause or arrest
 Can be identified from directCan be identified from direct
recording of sinus node pacemakerrecording of sinus node pacemaker
activity during an EP studyactivity during an EP study

10. AV Blocks:AV Blocks:
Divided in to incomplete andDivided in to incomplete and
complete blockcomplete 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 thirdComplete AV block,also known as third
degree AV blockdegree AV block

11. Location of the BlockLocation of the Block
 Proximal to, in, or distal to the His bundleProximal to, in, or distal to the His bundle
in thein the
atrium or AV nodeatrium or AV node
 All degrees of AV block may beAll degrees of AV block may be
intermittent or persistentintermittent or persistent

12. First Degree AV BlockFirst Degree AV Block
PR interval is prolonged 0.21-PR interval is prolonged 0.21-
0.40 seconds, but no R-R0.40 seconds, but no R-R
interval changeinterval change

14. Second-Degree AV BlockSecond-Degree AV Block
 There is intermittent failure of theThere is intermittent failure of the
supraventricular impulse to be conductedsupraventricular impulse to be conducted
to the ventriclesto the ventricles
 Some of the P waves are not followed by aSome of the P waves are not followed by a
QRS complex.The conduction ratio (P/QRSQRS complex.The conduction ratio (P/QRS
ratio) may be set at 2:1,3:1,3:2,4:3,andratio) may be set at 2:1,3:1,3:2,4:3,and
so forthso forth

15. Types Of Second-Degree AVTypes Of Second-Degree AV
Block:I and IIBlock:I and II
 Type I also is called WenckebachType I also is called Wenckebach
phenomenon or Mobitz type I andphenomenon or Mobitz type I and
represents the more common typerepresents the more common type
 Type II is also called Mobitz type IIType II is also called Mobitz type II

16. Type I Second-Degree AVType I Second-Degree AV
Block: WenckebachBlock: Wenckebach
PhenomenonPhenomenon
 ECG findingsECG findings
1.Progressive lengthening of the PR1.Progressive lengthening of the PR
interval until a P wave is blockedinterval until a P wave is blocked
2.Progressive shortening of the RR2.Progressive shortening of the RR
interval until a P wave is blockedinterval until a P wave is blocked
3.RR interval containing the blocked3.RR interval containing the blocked
P wave is shorter than the sum ofP wave is shorter than the sum of
two PP intervalstwo PP intervals

18. Type II Second-Degree AVType II Second-Degree AV
Block:Block:
Mobitz Type IIMobitz Type II
 ECG findingsECG findings
1.Intermittent blocked P waves1.Intermittent blocked P waves
2.PR intervals may be normal or2.PR intervals may be normal or
prolonged,but they remain constantprolonged,but they remain constant
3.When the AV conduction ratio is 2:1,it is3.When the AV conduction ratio is 2:1,it is
often impossible to determine whether theoften 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

20. High-Grade or Advanced AVHigh-Grade or Advanced AV
BlockBlock
 When the AV conduction ratio is 3:1 orWhen the AV conduction ratio is 3:1 or
higher,the rhythm is called advanced AVhigher,the rhythm is called advanced AV
blockedblocked
 A comparison of the PR intervals of theA comparison of the PR intervals of the
occasional captured complexes mayoccasional captured complexes may
provide a clueprovide a clue
 If the PR interval varies and its duration isIf the PR interval varies and its duration is
inversely related to the interval betweeninversely 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 likelytype I block is likely
 A constant PR interval in all capturedA constant PR interval in all captured
complexes suggests type II blockcomplexes suggests type II block

21. Complete (Third-Degree) AV BlockComplete (Third-Degree) AV Block
 There is complete failure of theThere is complete failure of the
supraventricular impulses to reach thesupraventricular impulses to reach the
ventriclesventricles
 The atrial and ventricular activities areThe atrial and ventricular activities are
independent of each otherindependent of each other

22. ECG FindingsECG Findings
 In patients with sinus rhythm andIn patients with sinus rhythm and
complete AV block, the PP and RRcomplete AV block, the PP and RR
intervals are regular, but the Pintervals are regular, but the P
waves bear no constant relation towaves bear no constant relation to
the QRS complexesthe QRS complexes

24. Bundle Branch BlockBundle Branch Block
• Left Bundle Branch BlockLeft Bundle Branch Block
1.Complete LBBB1.Complete LBBB
2.Incomplete LBBB2.Incomplete LBBB
• Rigt Bundle Branch BlockRigt Bundle Branch Block
1.Complete RBBB1.Complete RBBB
2.Incomplete RBBB2.Incomplete RBBB

25. Left Bundle Branch BlockLeft Bundle Branch Block
Electrocardiographic CriteriaElectrocardiographic Criteria
1.The QRS duration is >/- 120 ms1.The QRS duration is >/- 120 ms
2.Leads V5,V6 and AVL show broad and2.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

27. Causes Of LBBBCauses Of LBBB
 Hypertrophy, dilatation or fibrosis of theHypertrophy, dilatation or fibrosis of the
left ventricular myocardiumleft ventricular myocardium
 Ischemic heart diseaseIschemic heart disease
 CardiomyopathiesCardiomyopathies
 Advanced valvular heart diseaseAdvanced valvular heart disease
Toxic, inflammatory changesToxic, inflammatory changes
HyperkalemiaHyperkalemia
Digitalis toxicityDigitalis toxicity
Degenerative disease of the conductingDegenerative disease of the conducting
system (Lenegre disease)system (Lenegre disease)

28. Prevalence Of LBBBPrevalence Of LBBB
At age 50 is 0.4%, and at age 80 itAt age 50 is 0.4%, and at age 80 it
is 6.7%is 6.7%
In most subjects with LBBB,regional wallIn most subjects with LBBB,regional wall
motion abnormalities (akinetic ormotion abnormalities (akinetic or
dyskinetic segments in the septum,dyskinetic segments in the septum,
anterior wall or at the apex) are presentanterior wall or at the apex) are present
even in the absence of CAD oreven in the absence of CAD or
cardiomyopathycardiomyopathy

29. Incomplete Left Bundle BranchIncomplete Left Bundle Branch
BlockBlock
 Criteria for incomplete LBBB includeCriteria for incomplete LBBB include
1.QRS duration > 100 ms but < 1201.QRS duration > 100 ms but < 120
msms
2.Absence of a Q wave in leads V5,V62.Absence of a Q wave in leads V5,V6
and Iand I

30. Right Bundle Branch BlockRight Bundle Branch Block
 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 lead2.An rsr’,rsR’ or rSR’ pattern in lead
V1 or V2 and occasionally a wide andV1 or V2 and occasionally a wide and
notched R wave.notched R wave.
3.Reciprocal changes in V5,V6,I and3.Reciprocal changes in V5,V6,I and
AVLAVL

32. Causes of RBBBCauses of RBBB
1.After repair of the VSD1.After repair of the VSD
2.After right ventriculotomy2.After right ventriculotomy
3.Right ventricular hypertrophy3.Right ventricular hypertrophy
4.Increase incidence of RBBB among4.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 cushion6.Large ASD (secundum type) or AV cushion
defectdefect
7.Brugada Syndrome7.Brugada Syndrome

33. RBBB in the General PopulationRBBB in the General Population
 The incidence increased with ageThe incidence increased with age
1.Below age 30 the incidence is 1.31.Below age 30 the incidence is 1.3
per 1000per 1000
2.Between 30 and 44 it ranges from2.Between 30 and 44 it ranges from
2.0 to 2.9 per 10002.0 to 2.9 per 1000

34. Incomplete RBBBIncomplete RBBB
 Criteria for incomplete RBBB are theCriteria for incomplete RBBB are the
same as for complete RBBB exceptsame as for complete RBBB except
that the QRS duration is < 120 msthat the QRS duration is < 120 ms

35. Causes of Incomplete RBBBCauses of Incomplete RBBB
1.Atrial septal defect (RAD in secundum or1.Atrial septal defect (RAD in secundum or
sinus venosus type, LAD with ostiumsinus 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 the4.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

36. Fascicular BlocksFascicular Blocks
 The left bundle branch divides intoThe left bundle branch divides into
two fasciclestwo fascicles
1.Superior and anterior1.Superior and anterior
2.Inferior and posterior2.Inferior and posterior

37. Types Of Fascicular BlockTypes Of Fascicular Block
 Left anterior fascicular blockLeft anterior fascicular block
 Left posterior fascicular blockLeft posterior fascicular block
 Bifascicular BlockBifascicular Block
 Trifascicular BlockTrifascicular Block

38. Left Anterior Fascicular BlockLeft Anterior Fascicular Block
 Left axis deviation , usually -45 to -90 degreesLeft axis deviation , usually -45 to -90 degrees
 QRS duration usually <0.12s unless coexistingQRS duration usually <0.12s unless coexisting
RBBBRBBB
 Poor R wave progression in leads V1-V3 andPoor 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 with R wave in lead II > leadThere is RS pattern with R wave in lead II > lead
IIIIII
 S wave in lead III > lead IIS wave in lead III > lead II
 QR pattern in lead I and AVL,with small Q waveQR pattern in lead I and AVL,with small Q wave
 No other causes of left axis deviationNo other causes of left axis deviation

39. Causes of Left AnteriorCauses of Left Anterior
Fascicular BlockFascicular Block
1.Acute Myocardial Infarction1.Acute Myocardial Infarction
2.Hypertensive heart disease2.Hypertensive heart disease
3.Degenerative disease of the3.Degenerative disease of the
conducting systemconducting system
4.Myocardial fibrosis4.Myocardial fibrosis

40. Left Posterior Fascicular BlockLeft Posterior Fascicular Block
 Diagnostic Criteria includeDiagnostic Criteria include
1.QRS duration 100- <120 ms1.QRS duration 100- <120 ms
2.No ST segment or T wave changes2.No ST segment or T wave changes
3.Right axis deviation (100 degree)3.Right axis deviation (100 degree)
4.QR pattern in inferior leads (II,III,AVF)4.QR pattern in inferior leads (II,III,AVF)
small q wavesmall q wave
5.RS patter in lead lead I and AVL(small R5.RS patter in lead lead I and AVL(small R
with deep S)with deep S)
6.No other causes of right axis deviation6.No other causes of right axis deviation

41. Bifascicular Bundle BranchBifascicular Bundle Branch
BlockBlock
RBBB with either left anterior or leftRBBB with either left anterior or left
posterior fascicular blockposterior fascicular block
 Diagnostic criteriaDiagnostic criteria
1.Prolongation of the QRS duration to 0.121.Prolongation of the QRS duration to 0.12
second or longersecond or longer
2.RSR’ pattern in lead V1,with the R’ being2.RSR’ pattern in lead V1,with the R’ being
broad and slurredbroad and slurred
3.Wide,slurred S wave in leads I,V5 and V63.Wide,slurred S wave in leads I,V5 and V6
4.Left axis or right axis deviation4.Left axis or right axis deviation

42. Causes of Bifascicular BlockCauses of Bifascicular Block
1.Coronary artery disease1.Coronary artery disease
2.Degenerative disease of the conducting2.Degenerative disease of the conducting
systemsystem
3.Aortic stenosis3.Aortic stenosis
4.Hypertensive heart disease4.Hypertensive heart disease
5.Myocardial fibrosis5.Myocardial fibrosis
6.Infiltrative process6.Infiltrative process
7.Tetralogy of Fallot7.Tetralogy of Fallot
8.After cardiac transplantation8.After cardiac transplantation

43. Trifascicular BlockTrifascicular Block
 The combination of RBBB, LAFB andThe combination of RBBB, LAFB and
long PR intervallong PR interval
 Implies that conduction is delayed inImplies that conduction is delayed in
the third fasciclethe third fascicle

44. Indications For Implantation ofIndications For Implantation of
Permanent Pacing in Acquired AVPermanent Pacing in Acquired AV
BlockBlock Class IClass I
1.Third-degree AV block associated with1.Third-degree AV block associated with
a.Bradycardia with symptoms (C)a.Bradycardia with symptoms (C)
b.Arrhythmias and other medical conditions thatb.Arrhythmias and other medical conditions that
require drugs that result in symptomaticrequire drugs that result in symptomatic
bradycardia(C)bradycardia(C)
c.Asystole>/-3.0 seconds or any escapec.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 (Myotonice.Neuromuscular diseases with AV block (Myotonic
muscular dystrophy)muscular dystrophy)
2.Second-degree AV block with symptomatic2.Second-degree AV block with symptomatic
bradycardiabradycardia

45. Class IIaClass IIa
 Asymptomatic third-degree AV blockAsymptomatic third-degree AV block
with average awake ventricular rates ofwith average awake ventricular rates of
40 bpm or faster (B,C)40 bpm or faster (B,C)
 Asymptomatic type II second-degree AVAsymptomatic type II second-degree AV
blockblock (B)(B)
 First-degree AV block with symptomsFirst-degree AV block with symptoms
suggestive of pacemaker syndrome andsuggestive of pacemaker syndrome and
documented alleviation of symptomsdocumented alleviation of symptoms
with temporary AV pacingwith temporary AV pacing (B)(B)

46. Class IIbClass IIb
Marked first-degree AV block (>0.30Marked first-degree AV block (>0.30
second) in patients with LV dysfunctionsecond) in patients with LV dysfunction
and symptoms of congestive heartand symptoms of congestive heart
failure in whom a shorter AV intervalfailure in whom a shorter AV interval
results in hemodynamic improvement,results in hemodynamic improvement,
presumably by decreasing left atrialpresumably by decreasing left atrial
filling pressurefilling pressure (C)(C)

47. Class IIIClass III
Asymptomatic first-degree AV blockAsymptomatic first-degree AV block
(B)(B)
Asymptomatic type I second-degreeAsymptomatic 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- orlevel or not known to be intra- or
infra-Hisianinfra-Hisian (B, C)(B, C)
AV block expected to resolve andAV block expected to resolve and
unlikely to recur (eg,drug toxicity,unlikely to recur (eg,drug toxicity,
Lyme disease)Lyme disease) (B)(B)

48. Indications for PermanentIndications for Permanent
Pacing in Chronic BifascicularPacing in Chronic Bifascicular
and Trifascicular Blockand Trifascicular Block
1.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 whenSyncope 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 blockFascicular block with first-degree AV block
without symptoms.without symptoms. (B)(B)

49. Indications for Permanent PacingIndications for Permanent Pacing
After The Acute Phase OfAfter The Acute Phase Of
Myocardial InfarctionMyocardial Infarction
 Class IClass I
 Persistent second-degree AV block with bilateralPersistent second-degree AV block with bilateral
bundle branch block or third-degree AV blockbundle branch block or third-degree AV block
within or below the His-Purkinje system afterwithin or below the His-Purkinje system after
AMI.AMI. (B)(B)
 Transient advanced (second- or third-degree)Transient advanced (second- or third-degree)
infranodal AV block with bundle branch block.infranodal AV block with bundle branch block.
(B)(B)
 Persistent and symptomatic second- or third-Persistent and symptomatic second- or third-
degree AV block.degree AV block. (C)(C)

50. Indications Of Permanent PacingIndications Of Permanent Pacing
After the Acute Phase OfAfter the Acute Phase Of
Myocardial InfarctionMyocardial Infarction
(Continuation)(Continuation)
Class IIbClass IIb
 Persistent second- or third-degree AV block at the AVPersistent second- or third-degree AV block at the AV
node level.node level. (B)(B)
Class IIIClass III
 Transient AV block in the absence of intraventricularTransient AV block in the absence of intraventricular
conduction defects.conduction defects. (B)(B)
 Transient AV block in the presence of isolated leftTransient AV block in the presence of isolated left
anterior fascicular block.anterior fascicular block. (B)(B)
 Acquired left anterior fascicular block in the absenceAcquired left anterior fascicular block in the absence
of AV block.of AV block. (B)(B)
 Persistent first-degree AV block in the presence ofPersistent first-degree AV block in the presence of
bundle branch blockbundle branch block that is old or age indeterminate.that is old or age indeterminate.
(B)(B)