Prepared by:
DR. Ahmed Omer Bashehri
Anatomy & 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 Patterns
 SVT with Aberrancy
 Diagnosis 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.
Anatomy & Physiology of
Conductive system ( cont`d )
The electrical stimulus spreads simultaneously down
the Lt. & Rt. BBs into the ventricular myocardium by
way specialized conducting cells called Purkinje
Anatomy & Physiology of
Conductive system ( 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.
Anatomy & Physiology of
Conductive system ( 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
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 &
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.
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
Right Bundle Branch Block
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
Patho-physiology of
Conduction Disturbances &
Their Clinical Significance
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
Right Bundle Branch Block Criteria
V1 or V2 = rSR’ - “M” or rabbit ear shape
V5 or V6 = qRS
Large 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?
Right Bundle Branch Block
Patho-physiology of
Conduction Disturbances &
Their Clinical Significance
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
Left Bundle Branch Block
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 complex
V1 = QS ( or rS ) and may have a “ W ” shape to it.
V6 = R or notched R showing a “M” shape or
rabbit ears
Secondary T wave inversion
Secondary if in lead with tall R waves
Primary if in right precordial leads
Patho-physiology of
Conduction Disturbances &
Their Clinical Significance
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
 Cardiomyopathy
 Related to degenerative changes
N.B.: Most patients with LBBB have underlying LVH
Left Bundle Branch Block
RBBB versus LBBB
Fascicular Blocks
Recognition 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.
S 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.
Usually rS complex in lead I & a qR complex in
inferior leads.
Its diagnosis is by exclusion.
Left Anterior Fascicular Block (LAFB)
Initial QRS forces directed rightward (negative in
Lead I) and inferiorly (positive in Leads II and III
Subsequent predominant forces directed leftward
(positive in I) and superiorly (negative in II and III)
Left Posterior Fascicular Block (LPFB)
Initial QRS forces directed leftward (positive in
Lead I) and superiorly (negative in Leads II and III
Subsequent predominant forces directed rightward
(negative in I) and inferiorly (positive in II and III)
Left Posterior Fascicular Block
Bi & Tri Fascicular Blocks
Bifasicular 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 Aberrancy
In 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 Criteria
1) 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 VT
a) 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 Aberrancy
Clinical history – if the patient has had an MI in the
past?…it is VT until proven otherwise
 AV dissociation
 QRS morphology
 QRS axis
 Fusion beat
 Capture beat
Atrial Fibrillation with Preexcitation
A-V Dissociation, Fusion, and
Capture Beats in VT
Fisch C. Electrocardiography of Arrhythmias. 1990;134.
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 Criteria
This 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
Let`s Practice Some ECGs
Let`s Practice Some ECGs
Let`s Practice Some ECGs
Let`s Practice Some ECGs
‫أجمل التهاني وأسمى التبريكات المكللة بأجمل باقات الورد‬
‫المعبقة بنسمات الفل والياسمين والمعطرة بشذى النرجس‬
‫والرياحين تحملها طيور الحب والنورس نقدمها إلى زميلينا‬
‫والدكتورة ‪ /‬رؤى ياسين‬
‫الدكتور ‪ /‬فيصل الصبري‬
‫بمناسبة الخطوبة وعقبال ما نفرح بزواجكم إنشاء هللا‬

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