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Right Bundle Branch Block and More

The Patient:    These tracings are taken from a 75-year-old man who became weak while playing golf on a very hot day.  He was pale and diaphoretic.  He was hypotensive, but we do not know his BP reading. He denies chest pain or discomfort. The patient reported a history of lung cancer and hypertension. We have no other history, and unfortunately, no follow-up information.

ECG Number 1:           The first ECG shows the standard 12 leads.  The rhythm is sinus with frequent appearances of PAC couplets.  The sinus rate varies slightly from about 76 bpm to 68 bpm, tending to slow a bit after the premature atrial contractions.  There is a right bundle branch block, and the QRS duration is about .12 seconds (120 ms). The PR interval is slightly log at 223 ms.  We do not know what medications the patient is on, and we do not have an older ECG for comparison.

There are some interesting, if subtle, changes worth mentioning.  The QRS complexes in most leads are fragmented.  That is, they have notching in the terminal S or R waves that is not due to the bundle branch block. This can be a sign of scarring, and can also be considered an equivalent to a pathological Q wave.  Speaking of pathological Q waves, they are seen in the inferior leads, II, III, and aVF.  There are also prominent, though not large Q waves in V4 through V6, leads which normally do not have them. All this points to scarring and possibly long-term coronary artery disease, with possible old M.I.  In addition, the ST segments are not entirely normal.  There is ST depression in the inferior and low lateral leads, a little ST elevation in aVL.  Also, the SHAPES of the ST segments tend to be straight throughout the ECG, instead of the usual curved (concave up) appearance.

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Bifascicular Block

This ECG is from a 77 year old woman who was brought to the Emergency Department by EMS. She was found to be suffering from sepsis.

ECG Interpretation      The ECG shows the expected sinus tachycardia at 123 beats per minute.  There is significant baseline artifact, of the type usually seen with muscle tension.  The artifact makes it difficult to assess P waves and PR intervals.


What we do see is RIGHT BUNDLE BRANCH BLOCK and LEFT ANTERIOR HEMIBLOCK, also called LEFT ANTERIOR FASCICULAR BLOCK.  Together, these are called BIFASCICULAR BLOCK.  Most people have three main fascicles in the interventricular conduction system:  the right bundle branch and the two branches of the left bundle branch, the anterior-superior fascicle and the posterior-inferior fascicle.  In bifascicular block, two of the three are blocked.

The ECG criteria for right bundle branch block are:

     *     wide QRS (> .12 seconds)


     *     rSR’ pattern in V1 .  (the initial R wave may be hard to see, but the QRS will be predominantly upright.

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Right Bundle Branch Block With Probable Previous M.I.

This ECG was obtained from an 87-year-old man with chest discomfort.  We have no other clinical information.

ECG Interpretation   The rhythm is regular and fast, with P waves, at 95 beats per minute. So, it is normal sinus rhythm, but the rate is probably not “normal” for this patient.  The P waves are small, and difficult to see.  We suggest Lead I to best view the P waves in this example. This is a good opportunity to teach the value of evaluating rhythm strips in more than one simultaneous lead, as subtle features may not show up well in all leads.  There is a first-degree AV block, with a PR interval of 232 ms.

We see the right bundle branch block (RBBB) pattern: rSR’ in the right precordial leads (with a tiny q wave in V1, which is not typical of  RBBB).  The QRS is wide at 148 ms (.148 seconds).  The R prime (R’) represents the right ventricle depolarizing slightly after the left ventricle.  This terminal delay widens the QRS without affecting the depolarization or contraction of the left ventricle.  This delay can be seen in every lead, but is especially easy to see in Leads I and V6, where there is a wide little s wave.  It is normal for the T waves to be in a direction opposite that of the terminal wave (inverted in Leads V1 and III, for example.)

There is left axis deviation.  The causes of LAD are many.  It is not unusual for people with RBBB to also have a left anterior hemiblock (LAH), also called left anterior fascicular block.  The left anterior fascicle has the same blood supply as the right bundle branch.   LAH causes a frontal plane axis shift – instead of Lead II having the tallest QRS of the limb leads, Leads I and aVL will be the tallest upright QRS complexes of the six limb leads.  Lead II will be very small, or flat, or negative. However, the probability of pathological Q waves in the inferior leads offers a more likely explanation for the leftward axis shift.  The M.I. that would have caused these Q waves is old, as there are no acute ST changes.  It would, of course, help to know this patient’s history.

Right bundle branch block can make evaluating for ST segment elevation a bit tricky.  Occasionally, the terminal delay – especially in Leads III and aVF – can be mistaken for ST elevation.  The J points in this ECG all appear to be at the baseline, with no overt STEMI.


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

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.

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Right Bundle Branch Block With Machine Interpretation Error

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. 

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Inferior Wall M.I. and Right Bundle Branch Block

These ECGs were taken from a 76 year-old-man who was complaining of chest pressure for 20 minutes.  He had a remote history of coronary artery bypass graft surgery.

This case has several good teaching points, including:

Significant artifact.  The limb leads show artifact which is severe enough to hamper our assessment of the j point location. Every effort should be made to eliminate artifact.  Some measures that might help are:

        *  clean and slightly "rough up" the skin where the electrode will be placed.  A rough wash cloth or gauze pad will work.

        *  shave hair if necessary.

        *  avoid areas of movement if possible.  Precordial electrodes must be placed in specific spots, but limb leads may be placed anywhere on the limb or on the trunk if it is impossible to avoid movement on the limbs.

       *   use fresh electrodes that have been protected from drying out.

Subtle STEMI changes.   This patient has an inferior wall M.I., which was confirmed as a complete occlusion of the right coronary artery in the cath lab.  The ST elevation in Leads II, III, and aVF is subtle, and more difficult to measure because of the artifact.  However, the SHAPE of the ST segments is a giveaway - they are very straight.  A convex-upward shape is normal (see Lead I).  Also, Lead aVL shows typical ST DEPRESSION, as a reciprocal view of the STE in Lead III.  More ST depressions can be seen in Leads V1 through V3, and they end abruptly there.  These localized ST depressions represent a reciprocal view of the posterior (also called lateral) wall, and represent an "extension" of the inferior wall M.I. up the back of the heart.  A V4 Right lead was obtained and shows no measurable ST elevation, but the shape is straight to slightly "frowning", indicating that the right ventricle may soon have STE.  Repeat ECGs should be obtained to watch for more definite ST elevations.

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Bifascicular Block and Sinus Bradycardia

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.

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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.

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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.

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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.


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