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Hemiblock

Left Anterior Fascicular Block (Hemiblock)

Sun, 09/13/2015 - 22:10 -- Dawn

This ECG provides an example of LEFT ANTERIOR FASCICULAR BLOCK (LAFB).  It is from a 71-year-old woman for whom we have no other history.  She also has first-degree AV block and right bundle branch block.  RBBB and LAFB together are called bifascicular block.  It is not uncommon to see this type of bifascicular block, as the right bundle branch and the  anterior fascicle of the left bundle share a blood supply. 

The conduction system below the AV node consists of the Bundle of His, the left bundle branch, and the right bundle branch.  While there is some variation among individuals, most of us have two main fascicles, or branches, of the left bundle.  The ANTERIOR-SUPERIOR fascicle carries the electrical impulse to the anterior wall of the left ventricle, and the POSTERIOR - INFERIOR fascicle carries the impulse to the inferior area of the left ventricle.

Blocks can occur at any level in the conduction system, including left bundle branch block, right bundle branch block, left anterior fascicular block, left posterior block, and bi-fascicular blocks. LAFB can have many causes, including myocardial infarction, cardiomyopathies, fibrosis of the cartilagenous ring, and aortic valve disease.  Left anterior fascicular block is much more common than left posterior fascicular block. Both are also called hemiblocks.

When LAFB is present, the initial septal depolarization forces are still left to right, providing a small initial q wave in Lead I and a small r wave in Lead III.  After septal depolarization is complete, the activation vector moves inferiorly and to the right as the electrical wavefront moves through the left posterior hemifascicle and right bundle branch. The impulse finally makes its way to the left and superiorly via slow conduction through myocardium normally depolarized by the left anterior hemifascicle, which is blocked.  It is because the terminal left ventricular activation moves upward and toward the left that the  inferior leads have negative deflections.

Left Anterior Fascicular Block

Sun, 09/28/2014 - 23:39 -- Dawn

This ECG provides an example of LEFT ANTERIOR FASCICULAR BLOCK (LAFB).  It is from an elderly woman for whom we have no other history.

The conduction system below the AV node consists of the Bundle of His, the left bundle branch, and the right bundle branch.  While there is some variation among individuals, most of us have two main fascicles, or branches, of the left bundle.  The ANTERIOR-SUPERIOR fascicle carries the electrical impulse to the anterior wall of the left ventricle, and the POSTERIOR - INFERIOR fascicle carries the impulse to the inferior area of the left ventricle.

Blocks can occur at any level in the conduction system, including left bundle branch block, right bundle branch block, left anterior fascicular block, left posterior block, and bi-fascicular blocks. LAFB can have many causes, including myocardial infarction, cardiomyopathies, fibrosis of the cartilagenous ring, and aortic valve disease.  Left anterior fascicular block is much more common than left posterior fascicular block. Both are also called hemiblocks.

When LAFB is present, the initial septal depolarization forces are still left to right, providing a small initial q wave in Lead I and a small r wave in Lead III.  After septal depolarization is complete, the activation vector moves inferiorly and to the right as the electrical wavefront moves through the left posterior hemifascicle and right bundle branch. The impulse finally makes its way to the left and superiorly via slow conduction through myocardium normally depolarized by the left anterior hemifascicle, which is blocked.  It is because the terminal left ventricular activation moves upward and toward the left that the  inferior leads have negative deflections.

The diagnostic criteria for LAFB are:  LEFT AXIS DEVIATION (QRS axis between -45 degrees and -90 degrees); qR pattern in Lead I; rS pattern in Lead III; delayed activation time evident in Lead aVL - the time from onset of the QRS to the peak of the R wave is 45 ms or more. (This example barely makes that criteria); QRS duration normal or slightly wide, but not 120 ms or more (unless there is also RBBB).  LAFB also causes poor R wave progression in the precordial leads, with late transition and S wave present in V6.

Before deciding on a diagnosis of LAFB, you must rule out previous or acute INFERIOR WALL M.I.  The pathological Q waves that can occur with necrosis can cause a left axis deviation in the frontal plane.  The presence of a small r wave in Lead III rules out pathological Q wave in that lead.  If any fascicular block (hemiblock or bundle branch block) occurs during the course of an M.I., the patient should be watched carefully for progression of the block.  Be prepared to pace if necessary in that situation. 

Thanks to our Consulting Expert, Dr. Ken Grauer, for his editing assistance.

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

Thu, 08/21/2014 - 11:45 -- Dawn

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.

Atrial Pacing With Right Bundle Branch Block

Mon, 05/19/2014 - 12:32 -- Dawn

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". 

 

Right Bundle Branch Block With Left Posterior Fascicular Block

Mon, 05/13/2013 - 08:09 -- Dawn

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

 

Right Bundle Branch Block With Atypical QRS in V1 and LAFB or Ventricular Rhythm???

Wed, 03/27/2013 - 19:28 -- Dawn

This is quite an interesting ECG, and the ECG Guru would love to hear what you think about it.  What we do know is that it is a wide-complex bradycardia in a patient for whom we have no clinical data, except that she is a 51 year old female.  The rhythm is probably junctional, as no P waves are seen and the rhythm is regular.  The rate of 63 per minute would be consistent with that. Interestingly, no disassociated sinus P waves are seen.  All slow wide-complex rhythms should be evaluated for idioventricular origin, or AIVR.  The QRS in V1 shows an atypical right bundle branch block pattern.  We usually look for rSR', or "bunny ears",  but  this ECG shows an upright R wave with a smaller, slurred r wave before it.  What makes this look like RBBB is the prominent wide little S wave in V6 and in Lead I.  We question the R wave progression, too.  Do you think it is possible that the electrodes for V2 and V3 are switched?  The axis is leftward, causing Lead II to be nearly biphasic - it represents a synthesis of what is seen in Leads I and III.  This is enough left axis shift to diagnose a left anterior fascicular block (with RBBB = bifascicular block). 

This is a great ECG, and we can't wait to hear from all you ECG Gurus out there. Maybe we will need to adjust our diagnosis after we hear from you.

Sinus Bradycardia With First-Degree AV Block and Left Anterior Fascicular Block

Sun, 03/10/2013 - 01:13 -- Dawn

This is a good ECG for demonstrating sinus brady and first-degree AV block. It shows the sinus node in the process of slowing down. For your more advanced students, there is left axis deviation due to left anterior fascicular block (left anterior hemiblock). The ST segments are flat, suggesting coronary artery disease. The fourth (bottom) channel is a good rhythm strip. Just crop the image. Please refer to Dr. Grauer's interesting post on teaching hemiblocks on our Ask The Expert page.

Sinus Tach vs SVT In An Inebriated Patient

Sat, 12/29/2012 - 15:21 -- Dawn

This series of ECGs was obtained from a 60-year-old man who was involved in a one-car accident.  He sustained no injuries, but his blood alcohol level was far above the legal limit for intoxication at over 300 mmol/L.  ECG No. 1 shows the ECG obtained by paramedics in the field, which they incorrectly interpreted to be atrial fibrillation.  No medication was given.  The ER physician obtained ECG No. 2, and considered sinus tachycardia as the diagnosis, but also, because of the fast rate and the fact that the rate had not changed for at least 15 minutes, he considered SVT or atrial flutter with 2:1 conduction.  The ERP administered diltiazem (Cardizem) to the patient, which resulted in ECG No. 3.  The transition to the slower rate was not captured on rhythm strips, but the nurse's notes showed a gradual change over 15 minutes from a rate of 160 to 105/min.  

Usually, on the Instructors' Collection ECGs, we like to give the "answer".  In this case, however, there will undoubtedly be some discussion regarding what went on.  This discussion can be useful if you are teaching intermediate to advanced students.  Questions to consider:  1) Is the fast rhythm an SVT and, if so, which one?  2) Is it sinus tachycardia and, if so, what are the effects of the car accident and the alcohol?  3) Is the left anterior fascicular block relevant? (Criteria are left axis deviation, slightly widened QRS complex at 110 ms, no other obvious reason for the axis deviation). 4) Is the ST elevation in the inferior wall during the tachycardia a sign of acute M.I.?  The patient was lost to followup, so it is not known whether the ST changes were investigated.  Note the flat ST segment and inverted T waves in V1 during the tachycardia that resolve when the rate decreases. 

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Atrial Fib, Bifascicular Block, Pacemaker

Tue, 04/10/2012 - 12:53 -- Dawn

Lots of information in this ECG! The underlying rhythm is atrial fibrillation with a controlled rate. The QRS is .12 seconds in duration, with an rSR' pattern in V1 and a wide s wave in Leads I and V6, indicating right bundle branch block. In addition, the axis is leftward - Leads I and aVL are upright and Leads II, III, and aVF are negative. There is no other obvious reason for the left axis shift, and therefore, the diagnosis by exclusion is left anterior fascicular block. RBBB and LAFB often appear together, as the right bundle branch and the anterior fascicle of the left bundle share the same blood supply from the left coronary artery. ALSO, this patient has a right ventricular pacemaker, and is pacing appropriately when the atrial fib slows. Pacer spikes are not readily seen, but the width of the QRS, the axis of the wide QRS complexes (left), and the timing (after a pause) all support the paced rhythm diagnosis. V5 and V6 actually show a very tiny hint of a spike. The T wave inversions seen in the upright leads are common with RBBB, and are usually considered normal in this setting.

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