BBB widens the QRS (120ms or more). This widening is due to the fact that the ventricles are forced to contract sequentially, thus requiring more time. Other conditions widen the QRS; a common one would be ventricular rhythms either paced or spontaneous. A differentiating factor between BBB and ventricular rhythms would be the presence of an underlying supraventricular rhythm. Therefore, when a QRS of 120ms or more is produced by a supraventricular rhythm, think BBB. This rule applies in all leads.
The “classic” pattern for RBBB in V1 is an RSR.
Example 1 underlying rhythm sinus QRS width 160ms Example 2 underlying rhythm sinus QRS width 120ms
Have the participants review these four examples of V1 in the course guide and determine if the BBB is LBBB or RBBB.
Right Bundle Branch Block
Dr. Muhammad Imran Janjua
HO- MU 1
Normal Ventricular Conduction
• Normal Conduction
– fibers of LBB begin conduction
– impulse travels across inter ventricular
septum from left to right
• towards + electrode creates small r wave
– travels across ventricles causing
depolarization of both simultaneously
• LV contributes most to complex
– impulse travels away from + electrode
creates primarily negative complex
Right bundle branch block (RBBB) results from a defect in the heart's
electrical conduction system. There is a delay in or failure of transmission
of electrical impulses down the right bundle of the heart. As a result, the
right ventricle depolarizes by means of cell-to-cell conduction. These
impulses spread more slowly than usual from the inter ventricular septum
to the right ventricle. This delay in conduction results in the characteristic
ECG pattern which is a wide and notched QRS. Although conduction
down the right bundle is delayed, conduction down the left bundle is
normal. As result, the inter ventricular septum and left ventricle
depolarize in the normal fashion
Causes Of RBBB
1.After repair of the VSD
2.After right ventriculotomy
3.Right ventricular hypertrophy
4.Increase incidence of RBBB among population at high
6.Large ASD (secundum type) or AV cushion defect
Causes of Incomplete RBBB
1.Atrial septal defect (RAD in secundum or sinus
venosus type, LAD with ostium primum type)
3.Right ventricular dysplasia
4.Congenital absence or atrophy of the bundle
5.After CABG and in transplanted hearts
RBBB: Examination Findings
• Right bundle branch block is associated with a
persistently split second heart sound with normal
respiratory variation in the splitting interval.
RBBB: Lab Evaluation
• If there is a history of blunt trauma or any
symptoms to suggest polymyositis then troponin,
creatine kinase (CK) and an echocardiogram
should be obtained.
Anatomic locations of RBBB
1. Proximal, or central, RBBB: block is located
just distal to the bundle of His
2. Interruption between the proximal and distal
aspects of the right bundle branch
3. Distal RBBB
• The diagnostic criteria include:
• 1.QRS duration is >/- 120 ms
• 2.An rsr’,rsR’ or rSR’ pattern in lead V1 or V2
and occasionally a wide and notched R wave.
• 3.Reciprocal changes in V5,V6,I and AVL
• Fundamental Criteria
– Wide QRS
• > 100 ms (or, 0.10 sec)
– Supraventricular rhythm
• Criteria for incomplete RBBB are the same as for
complete RBBB except that the QRS duration is
< 120 ms
• RBBB in V1
– no change in initial impulse
• small r wave
– impulse depolarizes LV by
itself since RBBB
– RV depolarized by impulse
• it now contributes to complex
– travels toward + electrode
creating positive deflection
• In general treatment for right bundle branch block
is not necessary.
• These patients need not limit their activity.
• If the RBBB progresses to heart block, further
electrophysiologic testing may be necessary.
• Those patients who develop right bundle branch
block after surgery should undergo EKG testing
each year to evaluate for interval changes.
• Particular care should be taken to observe for the
development of sinus bradycardia,
supraventricular or ventricular ectopy.