Displaying 1 - 10 of 26
Dawn's picture

Left Bundle Branch Block

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. (https://LITFL.com/left-atrial-enlargement-ecg-library/) ECG criteria are not highly accurate for detecting atrial enlargement, and abnormal findings should be confirmed by anatomic measurement. (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2244611/).

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

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

Second-degree AV Block with 2:1 Conduction and Right Bundle Branch Block

This interesting ECG is a great one for your more advanced students who are ready to discuss the anatomical and physiological differences between the AV blocks, as opposed to just measuring PR intervals.  It shows a sinus rhythm with an atrial rate of 72/minute.  Second-degree AV block causes every other p wave to be blocked, resulting in a pulse rate of 36 beats per minute.  In addition, the ECG shows right bundle branch block, as evidenced by the wide QRS (136 ms), rsR' pattern in V1, and the wide little S wave in Lead I.

When second-degree AVB conducts 2:1, it can sometimes be difficult to determine if the block is Type I (occuring above the Bundle of His), or Type II (occuring at or below the Bundle of His).  This is because two p waves must be conducted in a row to see the tell-tale progressive prolongation of the PR interval seen in Type I (Wenkebach).

Two clues that this block is Type II are:  1) the presence of right bundle branch block.  Type II blocks are sub-Hisian blocks, often in the fascicles, and the right bundle branch block is a fascicle block.  Many Type II AV blocks show signs of right bundle branch block;   2) The non-conducted p waves occur well clear of the refractory periods of the preceding beats.  In Type I blocks, the QRS is eventually dropped because the p wave occurs in the refractory beat of the preceding QRS. Only one beat is missed.  In Type II blocks, p waves that SHOULD have conducted, don't.  Sometimes, more than one p wave in a row will be non-conducted.

Dawn's picture

Left Bundle Branch Block

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

This is an example of right bundle branch block - with a couple of twists.  It has the usual ECG characteristics of right bundle branch block:  widened QRS (154 ms), supraventricular rhythm (sinus bradycardia), and an rSR' pattern in V1.  In addition, wide little S waves are clearly seen in Leads I and V6.  This secures the diagnosis of right bundle branch block (RBBB).  Each QRS complex in every lead starts off with a very normal appearance, or morphology.  Then, as the right ventricle is depolarized late, an additional wave is "added on".  This is the R-Prime (R') in V1 and the S wave in Leads I and V6.

In most examples of RBBB, you will see the T wave point in the OPPOSITE direction of the terminal wave.  So, V1 should have a NEGATIVE T wave.  In this example, V2 and V3 should have also had negative T waves.  The upright T waves could be considered to have the same significance as inverted T waves in a normal ECG.  

Another interesting aspect to this ECG is the unusual morphology of the terminal S wave in most of the leads.  There appears to be a slight notch.  Lead V2 even appears to have ST elevation.  Perhaps some of our Gurus would comment on this.

This is a good ECG to use to show how the terminal R' and S waves can sometimes be confused with ST elevation and depression.  Lead III has a very flat T wave, and one might make the mistake of calling the R' wave "ST elevation".  The R' does not have the sloping shape of a normal ST segment and T wave.  Also, all the channels on the ECG are run simultaneously.  One needs only to look up at Leads I and II to see where the true T waves are - Lead III's T wave is directly under them.

This is a very good teaching ECG.  We look forward to hearing your comments.

Dawn's picture

Left Bundle Branch Block and Artifact

This ECG offers several teaching opportunities.  First, it is an example of left bundle branch block (LBBB).  It was obtained from a 53-year-old man who was undergoing a cardiac cath for chest pain.  Unfortunately, we do not have access to his past medical history or the results of his cath.  The ECG criteria for a diagnosis of LBBB are:  1) wide QRS complex; 2) supraventricular rhythm; 3) negative QRS in V1 and positive QRS in V6 and Lead I.  This ECG shows normal sinus rhythm at a rate of 88 bpm and a wide QRS at 158 ms (.158 seconds).  The QRS in V1 is negatively deflected and in V6 and Lead I it is positive.

In LBBB, as with any condition that significantly widens the QRS, there will be ST-T changes.  The ST segment will deviate in the opposite direction of the QRS.  In other words, there will be ST elevation in leads with negative QRS complexes and ST depression in leads with positive QRS complexes.  LBBB causes significant difficulty for those trying to diagnose acute ST elevation using ECG alone.  Excessive ST elevation in a lead where elevation is expected OR ST elevation in a lead where depression is expected should be considered to be abnormal.  At this point, you may find it useful to review Sgarbossa's Criteria regarding determining the presence of acute M.I. in the presence of LBBB.

LBBB can be a serious functonal problem for the patient, as the slow ventricular conduction that causes the wide QRS results in less-than-optimal cardiac output.  This associates LBBB with congestive heart failure, both as a cause of CHF and a result of CHF.  Many people with LBBB and CHF can be helped by cardiac resynchronization therapy - pacing both ventricles synchronously to narrow the QRS and improve cardiac output.  For an excellent article on cardiac pacing in general and CRT (page 2299), go to the 2013 European Society of Cardiology Guidelines as reported by the European Heart Journal, (2013) 34, 2281–2329 doi:10.1093/eurheartj/eht150

Dawn's picture

Acute Anterior-lateral M.I. With Right Bundle Branch Block and Left Posterior Fascicular Block

This ECG was obtained from a patient who suffered an occlusion of the left main coronary artery.  ST elevation is seen in Leads V1 through V6, as well as I and aVL.  This is an indicator that the circumflex artery is included in this M.I., and the occlusion is above the bifurcation of the LM and the circ.  The patient also has a right bundle branch block and a left posterior fascicular block.  This bi-fascicular block can be a dangerous complication of acute M.I., as two of the three main bundle branches are no longer functional.

The ECG shows typical ST depression, probably reciprocal to the elevation, in the inferior leads.

The right bundle branch block is diagnosed by the following criteria:  1) Wide QRS;  2) Supraventricular rhythm; and 3) rSR' pattern in V1 with Rs with a wide little s wave in Leads I and V6.

The left posterior fascicular block is diagnosed by right axis deviation and by ruling out other causes of right axis deviation.  In RAD, Lead III will have a taller positive ( R ) wave than Lead II, and a negative Lead I.

This type of occlusion is often called the "Widow Maker", and requires very rapid intervention to restore blood flow and prevent complicatons.  If there is good news, it is that there are no pathological Q waves, which would indicate necrosis, and this patient was taken quickly to a full-service cardiac center with interventional cath labs and open heart surgery available.

Dawn's picture

Left Bundle Branch Block

This is a good example of sinus rhythm with left bundle branch block.  There is some irregularity due to a PAC at the beginning.  The QRS is wide at 144 ms (.14 seconds).  There is also first-degree AV block, with a prolonged PR interval of 228 ms.  The criteria for diagnosis of left BBB are:  wide QRS, supraventricular rhythm, and a negatively-deflected QRS in V1 with a positive QRS in Leads I and V6.  

Left bundle branch block can be associated with many forms of heart disease, including CHF.  It can be permanent, transient, intermittent, or rate-related.  The wide QRS of LBBB significantly decreases cardiac output, causing poor perfusion symptoms in some people.

This ECG is a good one for your students who are just transitioning from reading rhythm strips to reading 12-lead ECGs.  It shows the value of multi-lead assessment of rhythms. You will notice that P waves are difficult to see in some leads.  Armed with the knowledge that the four channels on this ECG are run simultaneously, you can show the students how finding P waves in one lead will allow you to find them in the leads that are above and below that lead. 

Similarly, it can be difficult to see the QRS width in some leads.  The leads in the same vertical column can help you see the QRS's true width, even if part of the QRS is "flat" in the isoelectric baseline.

Dawn's picture

Left Bundle Branch Block With Left Atrial Enlargement

This ECG, kindly donated by Dr. Ahmed from India, is from a 70-year-old man shows a sinus rhythm at 80 bpm with left bundle branch block (LBBB), left atrial enlargement (LAE), and a premature ventricular contraction (PVC). The ECG criteria for LBBB is:  1) Wide QRS  - greater than or equal to .12 seconds;  2) Supraventricular rhythm;  3) QRS that is negative in V1 and positive in Leads I and V6. In leads with a positive QRS, we will see some ST depression, and in leads with a negative QRS, some ST elevation.  This is "normal" for the wide QRS rhythm, and does not indicate injury or ischemia, although it does not rule it out, either.  LBBB is an indicator of cardiac disease, but not specific to one etiology.

There is a PVC seen as the 8th beat from the left, and it gives you a chance to show your students a wide-complex beat that is NOT associated with a P wave and is premature, compared to the wide-complex SINUS beats with LBBB.  The PVC, being wide-complex, also has similar ST changes:  the ST segments and T waves are DISCORDANT with the QRS complexes.

The P waves show some signs of enlargement of the left atrium.  The P waves in Lead II are tall and pointed, and the P waves in V1 are biphasic.  Left atrial enlargement in a patient with LBBB would not be surprising, as both are associated with left ventricular dysfunction.  Patients with these ECG patterns should be thoroughly evaluated for congestive heart failure.  Patients with LBBB, low ejection fractions, and heart failure are treated with cardiac resynchronization therapy, using a pacemaker that paces the atria and each ventricle, synchronizing both the A-V coupling interval and the depolarization of the ventricles for optimum cardiac output.

Dawn's picture

Teaching Series: Atrial Fibrillation With Left Bundle Branch Block

This is a good example of atrial fibrillation with left bundle branch block.  You get two ECGs with this one, because the patient presented to EMS with a fast heart rate, and the rate was slowed with the drug diltiazem.  We do not have any other patient information, unfortunately.

In the first strip, we see a wide-complex tachycardia.  In an emergency situation, with an unstable patient, this rhythm could safely be treated using an emergency ventricular tachycardia (VT) protocol.  In fact, all WCTs should be considered to be VT until proven otherwise.  In most emergency settings, the unstable VT patient would be electrically cardioverted, which will often convert atrial fibrillation as well.  The stable patient with this rhythm would be treated with an antiarrhythmic drug, such as amiodarone.  This may convert or slow down atrial fib.  So, in the initial stages of treatment, differentiating between VT and A Fib is not the first priority.  Assessing the patient's hemodynamic stability and addressing the rate if necessary are the priorities.  

So, how do we know this is NOT VT?  It can be difficult, but in this case, the rhythm, even though fast, is very irregular.   VT is not always perfectly regular, but this irregularly-irregular rhythm points to atrial fibrillation. Also, the pattern of the QRS morphology fits with LBBB.  The criteria for LBBB are:  1) supraventricular rhythm, 2) wide QRS, 3) negative QRS in V1 with positive QRS in Leads I and V6.  If we assume the rhythm is atrial fibrillation, we meet the first criteria.  The other two are self-evident.

After the medication is administered, 10 minutes later, we see the rate slow down.  There is no change in the irregularly-irregular rhythm, and the LBBB pattern remains.  All that has changed is the rate and, hopefully, the patient's symptoms.  This confirms that the original rhythm was not VT.  

Remember, atrial fib lowers cardiac output because there is no P wave - no "atrial kick".  Also, the fast rate associated with new-onset atrial fib often compromises ventricular filling and cardiac output.   LBBB also has a deleterious effect on cardiac output.  Wide QRS complexes indicate that the ventricles are not contracting efficiently and synchronously.  The left ventricle is depolarizing by way of a slow wave of depolarization, rather than all the cells getting the message to depolarize at the same time.  Having these two conditions at the same time can have a very negative effect on cardiac output, leading to CHF.  The first step in treatment often involves simply slowing the rate to normal, which allows for better ventricular filling and decreases the workload on the heart.  Then, the fibrillation and bundle branch block can be addressed.


All our content is FREE & COPYRIGHT FREE for non-commercial use

Please be courteous and leave any watermark or author attribution on content you reproduce.