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Right bundle branch block

Acute M.I. With Right Bundle Branch Block and Atrial Pacing

Wed, 01/24/2018 - 22:08 -- Dawn

This ECG was taken from a 78-year-old man who was experiencing chest pressure in the morning, after having left shoulder pain since the night before. He has a history of hypertension and hypercholesterolemia, and has an implanted pacemaker.

What does the ECG show?  The ECG shows an atrial paced rhythm, with two premature beats, beats number 5 and 12.  These are probably PVCs.  The patient has a functioning AV conduction system, so the paced atrial beats are conducting through the AV node and producing QRS complexes.  In the interventricular conduction system, the impulse encounters right bundle branch block. This causes each QRS to have an “extra” wave attached at the end, representing slightly delayed depolarization of the right ventricle.  Instead of an “rS” pattern in V1, for example, we see “rSR’ “.  The slight delay causes the QRS to be widened, as we are measuring the two ventricles separately, rather than synchronously.

There is definite ST segment elevation in V2 and V3, and the shape of the ST segment is straight, having lost it’s normal “concave upward” appearance.  In an ECG taken three minutes later, the STE extends to V4.

Do the pacemaker or the right bundle branch block prevent us from diagnosing an ST-elevation M.I.?  The answer to that is a resounding “NO!” Pacemakers can sometimes make it difficult to assess ST elevation because ventricular pacing causes ST segment changes.  Pacing the right ventricle causes a depolarization delay in the left ventricle as the impulse travels “cell to cell” across the LV.  This means an RV-paced beat will resemble a PVC from the RV.  When LV depolarization is altered, repolarization will also be altered, causing ST elevation in leads with negative QRS complexes, and ST depression is leads with upright QRSs. These are called discordant ST changes. These changes are proportionate to the height or depth of the QRS, with very minimal or no ST changes in leads with short or biphasic QRS complexes.  We don’t have to worry about that in this situation – the pacemaker is not pacing the ventricles.

Right Bundle Branch Block With Machine Interpretation Error

Tue, 09/19/2017 - 14:33 -- Dawn

Today’s ECG is from a 74-year-old man for whom we have no clinical information.  It shows a “classic” right bundle branch block.  It also shows an example of the ECG machine getting some of the interpretation wrong.  An early mistake in the interpretative algorithm caused a cascade of inaccuracies.


     *   Supraventricular rhythm

     *   QRS .12 seconds (120 ms) in width

     *   rSR’ pattern in V1

     *   Small, wide S wave in Leads I and V6

In right bundle branch block, the initial part of each QRS complex represents the depolarization of the septum and left ventricle.  The right ventricle depolarizes late, and is represented by a terminal wave at the end of each QRS.  In V1, that terminal wave is the R’ and in I and V6 it is the small S wave. 

MACHINE MISTAKES  The first mistake the machine made was in measuring the QRS width. The machine says the QRS is .096 seconds (96 ms).  It is actually about .16 - .18 seconds.  Look at the second QRS in V1, and you will see that it extends almost the full width of a wide block (.20 sec).  It is apparent that the machine measured only the left ventricular portion of the QRS complex. Because of this error, the right bundle branch block was not noted. 

The mistake in measuring the QRS complex resulted in the machine misinterpreting the terminal wave as the ST segment.  This resulted in notations in capital letters warning of ST elevation and presence of myocardial ischemia.  The j points are actually at the baseline in all leads, indicating NO ST elevation. 

ST and T WAVE CHARACTERISTICS OF RBBB  Typically, in RBBB, the T wave will be opposite in direction from the terminal (RV) deflection.  So, when there is an R’, there will be T wave inversion.  The j point of the ST segment will not be altered, as the ST segment reflects what is happening in the LEFT VENTRICLE, which is depolarizing normally.  That means that an acute ST elevation M.I. will look the same in RBBB as it does without BBB. 

Ask The Expert

Tue, 09/19/2017 - 12:57 -- Dawn

Today’s expert is Dr. Jerry W. Jones, MD, FACEP, FAAEM

Jerry W. Jones, MD FACEP FAAEM is a diplomate of the American Board of Emergency Medicine who has practiced internal medicine and emergency medicine for 35 years. Dr. Jerry JonesDr. Jones has been on the teaching faculties of the University of Oklahoma and The University of Texas Medical Branch in Galveston. He is a published author who has also been featured in the New York Times and the Annals of Emergency Medicine for his work in the developing field of telemedicine. He is also a Fellow of the American College of Emergency Physicians and a Fellow of the American Academy of Emergency Medicine and, in addition, a member of the European Society of Emergency Medicine. 

 Dr. Jones is the CEO of Medicus of Houston and the principal instructor for the Advanced ECG Interpretation Boot Camp and the Advanced Dysrhythmia Boot Camp. 

Question:   What is the cause of an apparent right bundle branch block pattern in a paced rhythm?

Answer:  Is There a Pacemaker Wire Problem… or Not?

 During one of my orientations as a young internal medicine house officer, the cardiologist lectured to us on the essentials of how to check pacemakers. Since none of us had any ECG interpretation background our comprehension was less than sterling. But I remember him stressing the point that a properly paced pacemaker lead would result in a left bundle branch block pattern on the ECG. A right bundle branch block pattern in V1, on the other hand, meant that the pacemaker wire had inadvertently wandered into the left ventricle – a highly undesirable situation. 

“Not to worry,” he said. “Such things rarely happen and you will probably retire before seeing such a thing!” That evening I saw my first pacemaker 12-lead ECG with a right bundle branch block pattern in V1. Fate wasted no time with me.

I ordered a 3-view chest x-ray and as far as I could see, the wire looked like it was in the right ventricle where it was supposed to be. I called the cardiologist on-call who happened to be in the hospital at the time and he dropped by the ward. Back then, we didn’t have ultrasound or echo available. But he, too, was convinced the pacemaker wire was in the right ventricle. It really was and so I still hadn’t seen a RBBB pattern due to a pacer wire in the left ventricle. I still haven’t, but I have seen a number of pacemaker ECGs with a RBBB pattern in V1.

How do we know if such a finding represents a real left ventricular pacer wire or a pseudo-malplacement?

First, just be aware that a wire that really IS in the left ventricle is going to present with a RBBB pattern in V1. It will NOT ever present with a LBBB pattern. However, a wire that has been correctly placed in the RIGHT ventricle can – from time to time – present with a RBBB pattern in V1. In my years as an attending in the emergency department, I saw this seven or eight times.

Second, the axis of the pseudo-malplacement tends to demonstrate a significant left axis deviation, between -30 ° and    -90 °. Since the right ventricle is activated first, the vector finishes by pointing up and to the left. If the wire were actually located in the left ventricle, the mean frontal axis would be to the right of +90 °

Third, when we look in the precordial leads, we know that Leads V1 and V2 overlie the right ventricle and leads V5 and V6 overlie the left ventricle. Leads V3 and V4 are in between. If the pacemaker wire is in the right ventricle, whatever is causing it to have an RBBB pattern in V1 will disappear before V3. A pacemaker wire in the right ventricle will show a LBBB pattern (QS) by Lead V3. If the wire is truly in the left ventricle, the RBBB pattern will extend to V3 and usually beyond. So a quick check is this: if you see a RBBB pattern in V1 in a pacemaker patient, look at V3. If the RBBB pattern is in V3 also, the wire is truly in the left ventricle. If V3 has a predominately negative QRS (QS), the wire is safely in the right ventricle where it is supposed to be. 

A fourth check is to look for an S wave in Lead I. Remember: one of the most characteristic features of RBBB is that slurred S wave in Lead I (as well as the other left-sided leads). If the ECG shows an RBBB pattern in V1 and an S wave is present in Lead I, then that is most likely a real RBBB pattern and the wire has somehow made its way into the left ventricle.

Pseudo Malplacement of Pacemaker Wire

Anterior Wall M.I. With Bifascicular Block

Sat, 03/25/2017 - 15:13 -- Dawn

This ECG is taken from an 82-year-old man who called 911 because of chest pain.  He has an unspecified “cardiac” history, but we do not know the specifics. 

WHAT IS THE RHYTHM?  The heart rate is 69 bpm, and there are P waves before every QRS complex. The underlying rhythm is regular, with one premature beat that is wide without a P wave.  The PR interval is slightly prolonged at .25 seconds.  The rhythm is normal sinus rhythm with first-degree AV block and one PVC. 

WHY THE WIDE QRS?   The QRS complex is wide at .14 seconds. The QRS in V 1 has a wide R wave after a small Q wave.  This in consistent with right bundle branch block pattern, with loss of the normal initial small r wave (pathological Q waves).  The diagnosis of RBBB is further corroborated by the wide little S waves in Leads I and V6.  The QRS frontal plane axis is -66 degrees per the machine, and clearly “abnormal left” because the QRS in Lead II is negative, while the QRS in Leads I and aVL are positive.  This is left anterior fascicular block, also called left anterior hemiblock.  The combination of RBBB and LAFB is a common one, as the two branches have the same blood supply.  It is also called bi-fascicular block. 

WHAT ABOUT THE ST SEGMENTS?  The ST segments in leads V2 through V6 are elevated, and their shape is very straight, as opposed to the normal shape of coved upward (smile). Even though the amount of ST elevation at the J points appears subtle, the shape of the segments, the fact that they appear in related leads, and the fact that the patient is an elderly male with chest pain all point to the diagnosis of ANTERIOR WALL ST elevation M.I. (STEMI).  Additional ST changes include a straight shape in Leads I and aVL and ST depression in V1 and aVR.  

PATIENT OUTCOME  The patient was transported to a cardiac center, where he received angioplasty in the cath lab.  The left coronary artery was found to be occluded, and was repaired and stented.  He recovered without complications and was sent home in a few days.

Bifascicular Block and Sinus Bradycardia

Fri, 11/18/2016 - 20:30 -- Dawn

Today’s ECG is from a 75 year old man who has been experiencing syncope. 

Examination of the ECG shows a sinus bradycardia at just under 40 bpm.  There is a first-degree AV block, with a PR interval of about .28 seconds (280 ms).  There is a right bundle branch block.  The ECG criteria for right bundle branch block are:  supraventricular rhythm, wide QRS (120 ms in this case), rSR’ pattern in V1, and  a small, wide S wave in Leads I and V6.  There is actually a “terminal delay”, or extra wave at the end of each QRS complex, reflecting late repolarization of the right ventricle. 

This ECG also shows a left anterior fascicular block, also called left anterior hemiblock.  The left bundle branch usually has two main branches, the anterior-superior and the posterior-inferior.  ECG criteria for left anterior fascicular block are: left axis deviation with a small r wave in Lead III and a small q waves with tall R waves in Leads I and aVL.  There is also a prolonged R wave peak time (> 45 ms) in aVL. There is usually a slightly prolonged QRS, but in this case, there is widening of the QRS due to the RBBB.   Because the right bundle branch is blocked, and one fascicle of the left bundle is blocked, the patient is said to have a “bifascicular block”.  Only one fascicle remains available for conduction from the atria to the ventricles.

We have no information about what caused the conduction block in these two fascicles, but should the third fascicle fail, the patient will be in a complete AV block.  An AV block at the level of the bundle branches will result in an idioventricular escape rhythm – wide QRS complexes with very slow rates – which is a low-output rhythm.  

This patient has also had syncope, which was determined to be related to his bradycardia.  He had an AV sequential pacemaker implanted and did well.

Bigeminal Rhythm With Aberrant Conduction

Wed, 02/24/2016 - 20:09 -- Dawn

This ECG is a good example of sinus rhythm with aberrantly-conducted PACs.  The tracing was donated to the ECG Guru several years ago by Dr. Ahmed from Sanjiban Hospital in India.  We have no patient data for this tracing. 

The underlying rhythm here is normal sinus rhythm. Most of the parameters – rate, PR interval, and QRS duration – are normal.  The QTc interval, which is the QT interval corrected to a rate of 60 bpm, is prolonged at 568 ms.  We do not know the patient’s clinical condition or medications, so we cannot guess at the reason.  However, a prolonged QTc is associated with an increased risk of Torsades de pointes, a type of polymorphic ventricular tachycardia. 

The first three beats appear the same (Leads I, II, and III).  However, the first R-to-R interval is shorter than the second one.  This could be due to rate variation, a concealed sinus block, or a premature atrial contraction (PAC).   The P wave of the “early” beat, marked #1, looks slightly different from the other P waves in Lead II, but, because of the slow rate, there is no way to be sure without a longer rhythm strip.  After the possible PAC, the rhythm becomes coupled, probably atrial bigeminy, where every other beat is a PAC.  There are several mechanisms that cause grouped beating, but atrial ectopic bigeminy is the most common. Normally, PACs have different-looking P waves compared to the sinus beats.  In this ECG, the P waves are often buried in the preceding T waves, and are hard to evaluate. 

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.

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

Mon, 03/02/2015 - 23:19 -- Dawn

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.

Right Bundle Branch Block

Wed, 12/24/2014 - 21:21 -- Dawn

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.

Extensive Anterior-lateral M.I. With Right Bundle Branch Block

Sun, 11/16/2014 - 13:10 -- Dawn

This ECG depicts an extensive and ultimately, fatal, injury.  There is marked ST segment elevation in Leads V2 through V6 (anterior wall).  There is also ST elevation in Leads I and aVL (high lateral wall).  The ST elevation in aVR is indicative of a very proximal lesion in the left coronary artery, which supplies the anterior wall, including the anterior portion of the septum, the high lateral wall, and, in this case, the low lateral wall.  The inferior leads, II, III, and aVF, show reciprocal ST depression.

This is an old ECG - the computer readings of the rate and intervals is lost, as is the grid.  But the rate here appears to be about 80 bpm and the QRS is widened.  There is a right bundle branch block ECG pattern, which is not surprising given the extensive septal damage.  Normally, the criteria for RBBB on the ECG includes an rSR' pattern in V1 (seen here) and a small, wide s wave in Leads I and V6.  This s wave is not seen here, presumably due to the effects of the ST elevation in those leads.

What matters clinically in a patient like this is not whether there is RBBB or another type of interventricular conduction delay. This patient needs immediate restoration of blood flow through the LCA and intensive medical/nursing care.  As mentioned before, this patient did not survive, in spite of being brought to a hospital.  We do not know the exact mechanism of death or treatment course in this case.

If you are teaching students to use multiple leads in assessing rhythm, this is a great example of how one or two leads can be very misleading.  I have used this ECG's V4 in an excercise illustrating this concept.  Shown V4, many people would call this "AIVR" or "V Tach".  Seen in context with the other leads, it is obvious that we are looking at ST elevation that is as high as the R wave.  Two leads are better than one, and twelve are better than two.



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