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Bundle branch block

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Dawn's picture

Left Bundle Branch Block

Thu, 08/12/2021 - 15:08 -- Dawn

This ECG is taken from an elderly man with heart failure. 

The ECG   The first feature that might capture your attention is the wider-than-normal QRS complex, which is 160 ms (.16 seconds).  The rate is 58 bpm. We do not know the patient’s medications or baseline rate.  There are P waves present, and so the rhythm is SINUS BRADYCARDIA. The P waves are broad , > 110 ms in Lead II (red lines in close up) and bifid, with greater than 40 ms between the two peaks in Lead II (blue lines).  In V1, the P waves are biphasic, with the terminal negative portion greater than 40 ms duration (red lines). This meets the ECG criteria for LEFT ATRIAL ENLARGEMENT, or preferably, LEFT ATRIAL ABNORMALITY. ( ECG criteria are not highly accurate for detecting atrial enlargement, and abnormal findings should be confirmed by anatomic measurement. (

The QRS complexes, as mentioned, are wide. Because there is sinus rhythm, we know the delay in conduction is due to interventricular conduction delay, and not to ventricular rhythm.  This ECG meets the criteria for LEFT BUNDLE BRANCH BLOCK. 

·        Supraventricular rhythm 

·        Wide QRS (>.12 seconds)

Dawn's picture

Right Bundle Branch Block

Wed, 09/23/2015 - 22:14 -- Dawn

This ECG is from a 59-year-old man who was a patient in the Emergency Department with mild chest pain.  He had a history of coronary artery disease.  We have no other information about his medical history, medications, or outcome.

The ECG shows normal sinus rhythm and right bundle branch block.  The ECG criteria for right bundle branch block are: 1)  QRS wide at 120 ms or more (.12 sec. or more).                     2) Supraventricular rhythm.     3) Terminal waves indicating that the right ventricle is depolarizing late.  Because the right bundle branch is blocked, the left ventricle depolarizes first.  The QRS begins in a normal fashion.  The depolarization wave cannot access the right ventricle via the bundle branch, so it travels cell-to-cell across the right ventricle, causing a conduction delay.  This delay in depolarizing the right ventricle is seen on the ECG as a separate, terminal wave on the QRS.  In V1, it is seen as an R' wave, making the QRS have an rSR' pattern in most cases.  In Leads I and V6, there will be a wide, slurred S wave, causing an Rs pattern.  The frontal plane axis can be difficult to determine, as the first part of the QRS is from the left ventricle and the second part is from the right ventricle.

The causes of right bundle branch block are many.  The website, Life In the Fastlane has a good quick reference. 

This patient has a slightly prolonged QTc interval at 469 ms, for which we do not know the reason, lacking clinical information.  The QT interval measures the total time it takes to depolarize and repolarize the myocardium, and it is measured from the beginning of the QRS to the end of the T wave.  The QT interval lengthens naturally in slow rates, and shortens with faster rates.  The QTc has been mathematically corrected to a rate of 60/min.   A good rule of thumb is the QT interval should be less than half the RR interval of the preceding beat. A long QT interval (>500 ms) has been associated with increased risk of torsades de pointes.

Dawn's picture

Left Bundle Branch Block

Tue, 02/17/2015 - 21:54 -- Dawn

This ECG shows a “classic” left bundle branch block pattern. 

The ECG criteria for left bundle branch block are:

·        Wide QRS (.12 seconds or greater)

·        Supraventricular rhythm (ventricular rhythms do not travel via the LBB)

·        The QRS in V1 is negative, and the QRS in Leads I and V6 are positive. 

The left bundle branch (LBB) can be blocked permanently, temporarily, intermittently, or in the because of a fast rate.  When the LBB is blocked, conduction proceeds from the AV junction down the right bundle branch, depolarizing the right ventricle.  The impulse travels from the right ventricle across the left ventricle, cell by cell.  Conduction is slower this way, and there is asynchrony of the ventricles. This slow conduction and asynchrony of the two ventricles causes widening of the QRS complex.

NOTE:  It is "normal" for wide-complex rhythms to have ST segment elevation in leads with negative QRS complexes and ST depression in leads with positive QRS complexes.  This can make it a bit difficult to determine the ST changes of acute M.I. 



Dawn's picture

Right Bundle Branch Block

Tue, 11/12/2013 - 14:03 -- Dawn

This ECG shows a normal sinus rhythm at 73/min. and a right bundle branch block.  The diagnostic characteristics of RBBB are:  wide QRS (greater than .12 sec.), supraventricular rhythm (in this case NSR), and an rSR' pattern in V1 with a small, wide S wave in Leads I and V6.  The R' and small s waves represent the right ventricle depolarizing slightly AFTER the left ventricle.  In fact, in RBBB, each lead should look pretty normal at first, with a terminal right ventricular depolarization wave added to each QRS complex.  This is because the left ventricle depolalrizes normally.  In this patient, R waves progress fairly soon in the precordial leads (V1 through V2).  It is not known in this case if it is due to poor electrode placement or patient causes.

Dawn's picture

Right Bundle Branch Block

Sat, 11/03/2012 - 00:06 -- Dawn

This ECG is from a healthy young man in his 20's.  He was born with a ventricular septal defect (VSD) that was surgically repaired when he was a toddler.  He now has a right bundle branch block, which could be a result of the defect, or the surgery.  This is a good ECG for the Instructors' Collection because it clearly shows all the ECG characteristics of right bundle branch block:  wide QRS in a supraventricular rhythm (in this case, NSR), rSR' pattern in V1, wide or "slurred" S waves in Leads I and V6.  There is no rhythm strip below the 12 leads in this ECG, but there is no rhythm disturbance.

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