bundle branch block

BUNDLE BRANCH BLOCK

Prepared by: DR. Ahmed Omer

Bashehri

OBJECTIVESAnatomy & Physiology of Conductive

system.Blood Supply of Conductive System.Patho-physiology of Conduction

Disturbances & Their Clinical Significance: BBBs Fascicular Blocks Bi & Tri Fascicular Blocks Pacemaker PatternsSVT with AberrancyDiagnosis of AMI on top of LBBB

Anatomy & Physiology of Conductive system

Normally, cardiac stimulation starts in the SA node from which the stimulus spreads first through the RA & then into LA & so the SA node functions as the normal pacemaker of the heart.

The electrical stimulus then spreads to specialized conduction tissues in the AV junction which includes the AV node & bundle of His, & then into the Lt. & Rt. bundle branches which transmit the stimulus to the ventricular muscle cells.

The upper part of the AV junction is the AV node & the lower part is called the bundle of His which divides into 2 main branches: the RBB & LBB which in turn subdivided into LAF & LPF.


( cont`d )The electrical stimulus spreads simultaneously down the Lt. & Rt. BBs into the ventricular myocardium by way specialized conducting cells called Purkinje fibers .


( cont`d )

Normal conduction speed through the bundles is about 0.1 seconds & this is the reason the

normal width of QRS complex is equal or less than 2.5 small squares .


( cont`d )The 1st part of the ventricles to be stimulated is

the Lt. side of ventricular septum & on the normal ECG, this septal depolarization produces a small septal r wave in lead V1 & a small septal q wave in lead V6. Soon after, the depolarization spreads to the main mass of the Lt. & Rt. ventricles by way of LBB & RBB. Since the LV is normally electrically predominant, producing deep S waves in the Rt. chest leads & tall R waves in the Lt. chest leads.

Blood Supply of Conductive System

In most individuals the RCA is the most frequent blood supply to the SAN 60 % & AVN 90 % while the LCX supplies the remaining percentage, SAN 40 % AVN 10 %

The Bundle of His is supplied from the AV branch of RCA with small contribution from septal perforators of LAD

After division of His bundle, the septal perforators of LAD supply the Rt. bundle with collaterals from the RCA & LCX

The LAF is supplied from LAD while the proximal portion of LPF receives dual blood supply from nodal artery, generally a branch of RCA, & from LAD.

The distal portion of the LPF is supplied from 2 sources: the anterior & posterior septal perforating arteries.

N.B: LAF IS VERY SENSITIVE TO ISCHEMIA

Blood Supply of Conductive System ( cont`d )

Patho-physiology of Conduction

Disturbances & Their Clinical Significance

Clearly, RBBB should not affect the septal & LV depolarization so the change in the QRS complex produced is a result of delayed right ventricular depolarization ( 3rd phase )

With RBBB, lead V1 typically shows an r SR` complex with a broad R` wave & lead V6 shows a qRS complex with a broad S wave.

Right Bundle Branch Block

First Phase will be normal

Second Phase- Normal

Third Phase- ?

After the left ventricle has completely depolarized, the right ventricle continues to depolarize


1 .r wave in V1 q wave in V6

2 .S wave in V1 R wave in V6

3 .R’ wave in V1 S wave in V6

1. 2. 3.

RBBB also produces 2ry changes ( TWIs in the Rt. chest leads ) which are characteristic finding with RBBB because they reflect just the delay in ventricular stimulation.



Clinical Significance: Normal variant PE ASD with Lt. to Rt. shunt Chronic pulmonary disease with PHT Valvular lesions as PS Related to chronic degenerative changes CAD

Right Bundle Branch Block Criteria

V1 or V2 = rSR’ - “M” or rabbit ear shape

V5 or V6 = qRSLarge R waves

Right chest leads: T wave inversion (“secondary changes” since they reflect a delay in depolarization not an actual change in depolarization)

Complete RBBB: QRS > 0.12 sec.

Incomplete RBBB: QRS = 0.10 to 0.12 sec.Don`t forget the causes of tall R wave in

V1……..DDx?

By itself RBBB not require any specific treatment but in acute anterior MI with new RBBB indicate the increased risk of CHB especially when associated with hemiblocks.

Conversely to RBBB, LBBB affects the early septal depolarization so the normal pattern is blocked. Thus the 1st major ECG change produced by LBBB is a loss of the normal septal r wave in lead V1 & the normal septal q wave in lead V6. As a result, lead V1 typically shows a wide entirely negative QRS ( QS ) complex & lead V6 shows a tall wide, entirely positive ( R ) wave. Just as 2ry TWIs occur with RBBB they also occur with LBBB.



Left Bundle Branch Block

Loss of septal R in V1 and septal Q in V6.

Wide QRS

Negative in V1

Positive in V6


1 .r wave in V1 R wave in V6

2 .S wave in V1 R wave in V6

Left Bundle Branch Block Criteria

Wide QRS complexV1 = QS ( or rS ) and may have a “ W ” shape to it.V6 = R or notched R showing a “M” shape or rabbit earsSecondary T wave inversionSecondary if in lead with tall R wavesPrimary if in right precordial leads

Unlike RBBB, LBBB is usually a sign of organic heart disease & so it may be the first clue to 4 previously undiagnosed but clinically important abnormalities:

Advanced CAD VHD HHD Cardiomyopathy Related to degenerative changes



N.B.: Most patients with LBBB have underlying LVH

RBBB versus LBBB

?

?

Fascicular BlocksRecognition of fascicular blocks on the ECG is

intimately related to the subject of axis deviation & surprisingly does not markedly widen the QRS complex. Specifically, LAFB results in marked LAD; LPFB produces marked RAD.

LAFBS wave in lead aVF equals or exceed R wave in

lead I.Lead a VL usually shows qR complex with rS

complexes in inferior leads.LPFBUsually rS complex in lead I & a qR complex in

inferior leads.Its diagnosis is by exclusion.

Left Anterior Fascicular Block (LAFB)

I II III

Initial QRS forces directed rightward (negative in Lead I) and inferiorly (positive

in Leads II and III

rS rSqR

Subsequent predominant forces directed leftward (positive in I) and superiorly (negative in II and III)

Left Posterior Fascicular Block (LPFB)

rS qR qR

I

II III

Initial QRS forces directed leftward (positive in Lead I) and superiorly

(negative in Leads II and IIISubsequent predominant forces directed rightward (negative in I) and inferiorly (positive in II and III)

Left Posterior Fascicular Block

Bi & Tri Fascicular BlocksBifasicular block indicates blockage of any two

of the three fascicles e.g. RBBB with LAFB produces RBBB pattern with marked LAD; RBBB with LPFB produces RBBB pattern with RAD.

Bifascicular blocks are potentiall significant……why?

Therefore the acute development of new bifascicular block during acute anterior MI is an important warning signal of possible impending CHB.

Bifascicular Block

SVT with AberrancyIn some cases, a supraventricular

tachycardia can present as a wide complex tachcyardia. The brugada criteria were established to distinguish SVT with aberrancy from VT.

Steps 1-3 can be helpful in distinguishing VT from an SVT with aberrancy.

Step 4 is included as a reference, as in some cases determining a right bundle from left bundle pattern may be helpful in localizing location of the VT (RVOT vs. LV origin).

Brugada Criteria1) Lack of RS complex in the precordial leads

2) When RS complex is present, whether the longest interval in any precordial lead from the beginning of the R wave to the deepest part of the S wave is greater than 100 ms

3) Presence of AV dissociation

4) Both leads V1 and V6 fulfill criteria for classic VTa) Look for RBBB morphology in V1: - Monophasic R wave in V1 - Notched R wave - QR complex in V1

Brugada Criteria (Cont`d )b) RBBB morphology in V6 - R to S ratio < 1 (R wave smaller than the S wave) - QS pattern c) LBBB pattern in V1 or V2 - Broad R wave (>0.04s) - Notched downslope in S wave - Onset of R wave to the nadir of the S wave > 0.06 s

d) LBBB pattern in V6 - Presence of any Q wave, QR, or QS favors VT

Aberrancy with an SVT has two major mechanisms: BBB & WPW preexcitation

Electrocardiographic Differentiation of VT vs. SVT

with AberrancyClinical history – if the patient has had an MI

in the past?…it is VT until proven otherwiseAV dissociationQRS morphologyQRS axisFusion beatCapture beat

Atrial Fibrillation with Preexcitation

A-V Dissociation, Fusion, and Capture Beats in VT

Fisch C. Electrocardiography of Arrhythmias. 1990;134.

ECTOPY FUSION CAPTURE

V1 E F C

Sgarbossa Criteria

AMI on top of LBBB (Sgarbossa Criteria )

LBBB is always pathological and can be a sign of myocardial infarction. The criteria (Sgarbossa) that can be used in case of a LBBB and suspicion of infarction are:

ST elevation > 1mm in leads with a positive QRS complex (concordance in ST deviation) (score 5)

ST depression > 1 mm in V1-V3 (concordance in ST deviation) (score 3)

ST elevation > 5 mm in leads with a negative QRS complex (inappropriate discordance in ST deviation) (score 2)

Sgarbossa CriteriaThis criterion is sensitive, but not specific for

ischemia in LBBB. It is however associated with a worse prognosis, when present in LBBB during ischemia

At a score-sum of 3, these criteria have a specificity of 90% for detecting a myocardial infarction

During right ventricular pacing the ECG also shows left bundle brach block and the above rules also apply for the diagnosis of myocardial infarction during pacing, however they are less specific

LBBB with AMI

Let`s Practice Some ECGs

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bundle branch block

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