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

Submitted by Dawn on Mon, 03/02/2015 - 23:19

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

Right Bundle Branch Block

Submitted by Dawn on Wed, 12/24/2014 - 21:21

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

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

Submitted by Dawn on Thu, 08/21/2014 - 11:45

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

Atrial Pacing With Right Bundle Branch Block

Submitted by Dawn on Mon, 05/19/2014 - 12:32

No instructor's collection should be without an atrial paced rhythm OR a right bundle branch block.  Here, you get both.  First, the atrial pacing.  This patient had a sinus node problem, but his AV conduction system was functional (if not perfect).  At this time, he is able to conduct impulses from the atria to the ventricles.  What he cannot do is reliably produce the impulse in his atria.   So, this pacemaker is currently pacing the right atrium, producing a paced "P" wave, which is then conducted to the ventricles.  The fifth beat on the strip shows a "native" beat - one produced by the patient.  No P wave is seen, so it is presumed to be a junctional beat.

As for conduction through the ventricles, there is a right bundle branch block.  The left bundle branch is ensuring that the ventricles receive the depolarization "message", and the ventricles are depolarizing and contracting.  However, the right ventricle gets the message a little late, since is arrives from the left ventricle, and not through a functioning right bundle branch.  This produces a terminal wave on each QRS that represents this delayed depolarization of the right ventricle.  In leads oriented to the left side of the heart, like I and V6, it is seen as a wide little S wave.  In V1, which is oriented to the patient's right, we see an R prime (R'), producing the easily-recognizable rSR' pattern of RBBB.

For your more advanced students, this patient has atypical T waves for RBBB.  Normally, the T waves axes should be OPPOSITE that of the terminal portion of the QRS.  So, Lead V1 correctly shows an inverted T wave, since the R' is a positive deflection.  There are inverted T waves in Leads III, aVF (II is biphasic), as well as in V4, V5, and V6.  We expected upright T waves here. Because we do not have clinical information for this patient, we will call them "non-specific" T wave changes, remembering that inverted T waves can be a sign of ischemia.

ALSO:  As noted in Dave Richley's comment below, there is a left axis deviation, with a negative Leads II, aVF and III, and a positive I and aVL.  This  indicates left anterior fascicular block, which is rather common with RBBB, since the right bundle branch and the left anterior fascicle share a blood supply. So, this person as a "bi-fascicular block". 

 

Dawn's picture

Right Bundle Branch Block With Left Posterior Fascicular Block

Submitted by Dawn on Mon, 05/13/2013 - 08:09

This is a good clear example of right bundle branch block with left posterior fascicular block.  The RBBB is diagnosed by the following criteria:  wide QRS (.12 sec), supraventricular rhythm (NSR), an rsR' pattern in V1, and wide little s waves in I and V6.  The LPFB is inferred by the right axis deviation (Lead III QRS is a bit taller than Lead II and Leads I and aVL are negative), and the fact that there is no other obvious cause for right axis shift noted in this patient.  This constitutes a BIFASCICULAR BLOCK.  The ventricles are being depolarized by way of the anterior fascicle.  In addition, there are slight ST elevations in many leads, with an upward coving in the anterior-septal leads (V1, V2, V3).  Depending upon the patient's history and presentation, this could represent a recent M.I. or pending issues. The borderline first-degree AV block may be of concern in this patient, since first-degree AVB is associated with progression of bifascicular block to complete heart block.  Reference:  Ann Card Anaest, 2010 Jan-Apr;13(1):7-15. doi: 10.4103/0971-9784.58828

 

Dawn's picture

Recent Anterior-Septal M.I. With Right Bundle Branch Block

Submitted by Dawn on Thu, 04/18/2013 - 22:17

This is an ECG from a 95 year old man who was recovering from an anterior-septal wall M.I.  Other clinical data for this patient has been lost, except that he suffered a new right bundle branch block during this M.I.  The ECG shows pathological Q waves in V1, V2, and V3, consistent with permanent damage (necrosis) in the anterior septal wall.  The ST segments in those leads are coved upward.  Even though the J points are not elevated, this ST segment shape suggests recent injury.  The classic RBBB pattern is present:  wide QRS, rSR' pattern in V1, and wide little s waves in I and V6.  It is not known why the overall voltage is low in this patient.

Dawn's picture

Normal Sinus Rhythm With Aberrantly-Conducted PACs

Submitted by Dawn on Tue, 04/02/2013 - 22:00

This is a normal 12-Lead ECG with two PACs that are aberrantly conducted in a right bundle branch block pattern. (Sixth and ninth beats). In the PACs, the QRS is slightly wider than the normal beats.  The aberrantly-conducted beats have an rsR' pattern in V1, and a wide little S wave in aVL. No PACs are seen in Lead I to demonstrate the wide S wave.  This represents a right bundle branch block pattern, which is a common form of aberrancy, and is rate-related.  That is, the PAC occurs early in the cycle, catching the right bundle branch is a refractory state and unable to depolarize.  Slower beats are easily acommodated by the right bundle branch.

Dawn's picture

Right Bundle Branch Block With Left Anterior Fascicular Block

Submitted by Dawn on Thu, 02/07/2013 - 23:00

This is a nice, clear right bundle branch block pattern: wide QRS, supraventricular rhythm (NSR), and rSR' pattern in V1. Wide little s waves in Leads I and V6 are also diagnostic. The left axis deviation indicates a left anterior fascicular block, since there is no other apparent reason for the left axis deviation, such as pathological Q waves or LVH. Left anterior fascicular block is a diagnosis of exclusion, also considering that RBBB and LAFB are often seen together (bifascicular block), since the two fascicles have the same blood supply.


Dawn's picture

Third-degree AV Block and Junctional Escape Rhythm With Right Bundle Branch Block and Prolonged QTc Interval

Submitted by Dawn on Sat, 01/26/2013 - 13:48

This ECG is from a 70 year old woman for which we have, unfortunately, no clinical information.  It shows a sinus rhythm with a rate of about 72 bpm (NSR) with AV dissociation caused by third-degree heart block.  The escape rhythm is junctional at a rate of 38 bpm.  There appears to be a right bundle branch block, based on the QRS duration of 132 ms, and a wide S wave in Leads I and V6.  The precordial leads do not show the usual RBBB pattern of rSR' in V1 and V2, and the r wave progression is poor (non-existent).  This is felt to be due to poor lead placement (a good teaching point).  Of interest, the ECG machine has reported a "severe right axis deviation" based on the tall upright R wave in aVR and the deep S in avF.  In RBBB, the first part of the QRS represents left ventricular depolarization, and the terminal wave represents the delayed right ventricle.  In effect, the two ventricles have their own electrical axes, which we can see because the ventricles are not depolarizing simultaneously.  The axis of the LV appears to be normal in this tracing.

In addition to the above, this patient has a very prolonged QT interval.  The QT is longer in bradycardic rhythms, but when corrected to a standard of 60 bpm (QTc), this patient's QT interval is still prolonged at QTc: 552 ms.  Without clinical data, we cannot speculate  as to why this patient's QTc is prolonged, but it can be a very dangerous situation.  Follow the links for more information on QT prolongation and Torsades de Pointes and Long QT Syndrome.

As always, we welcome comments from our members adding insight to this interesting ECG, and also questions you would like to ask our Guru members.

Dawn's picture

Right Bundle Branch Block and Previous Anterior Wall M.I.

Submitted by Dawn on Sat, 12/22/2012 - 13:41

This example of previous anterior wall M.I. with right bundle branch block is from a 95-year-old man.  He survived an anterior-septal M.I. caused by an occlusion of the left anterior descending branch of the LCA. The septum was involved in the damaged area, and the patient was left with a right bundle branch block.  The pathological Q waves in Leads V1 through V3 show the location of permanent damage, or necrosis.

In this case, the usual rSR' pattern of right bundle branch block is replaced by qR, indicating loss of the initial r wave due to the M.I.

Review of RBBB criteria:  wide QRS, rSR' pattern in V1, and Rs with a slurred s wave in I and V6.  These criteria must be present in a SUPRAVENTRICULAR rhythm to diagnose RBBB.

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