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Left bundle branch block

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Instructors' Collection ECG: Wide Complex Tachycardia

Fri, 10/09/2020 - 14:30 -- Dawn

The Patient   A 64-year-old woman has called 911 because she has chest discomfort radiating to her left arm, palpitations, weakness, and a headache.  She had a valve replacement (we do not know which valve) two weeks ago and has a healing incision over her sternum.  She is found sitting in a chair, pale, cool, and diaphoretic. Her blood pressure is 94/palp.  Her pulse rate is 196 bpm and weak. She is afebrile.

ECG #1   This ECG shows a wide-complex tachycardia at 196 bpm.  The QRS complexes are .132 seconds in duration, per the ECG machine. The rate is too fast to appreciate whether there are P waves present.  We did not see the onset of the tachycardia, but with a rate this fast and regular, it is most likely a reentrant rhythm, rather than sinus tachycardia.  An abrupt onset of the rhythm would point to a diagnosis of a reentrant rhythm, either ventricular tachycardia (VT) or paroxysmal supraventricular tachycardia (PSVT). 

There is an important rule in emergency medical care:  a wide-complex tachycardia should be treated as VT until and unless it is proven to be something else.  The most likely alternate interpretation is PSVT with aberrant conduction, which usually takes the form of left or right bundle branch block. Fortunately, the paramedics on this call have a protocol for treating WCT that includes electrical cardioversion for the unstable patient, and amiodarone for the stable patient.  This protocol serves both possibilities, VT and PSVT, well.  The patient’s perfusion status and BP made her borderline in this determination, but she was alert and oriented, so the paramedics opted for administering the amiodarone while they prepared to electrically cardiovert.

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Wide Complex Tachycardia

Fri, 05/01/2020 - 16:19 -- Dawn

The Patient:   The details of this patient’s complaints and presentation are lost, but we know he was a 66-year-old man who was being treated in the Emergency Department. His rhythm went from sinus tachycardia with non-respiratory sinus arrhythmia to multi-focal atrial tachycardia (MAT) to wide-complex tachycardia. The WCT lasted a few minutes and spontaneously converted to an irregular sinus rhythm.

Wide-complex tachycardia:  Ventricular tachycardia or aberrantly-conducted supraventricular tachycardia?  When confronted with a wide-complex tachycardia, it can be very difficult to determine whether the rhythm is ventricular or supraventricular with aberrant conduction, such as bundle branch block. The patient’s history and presentation may offer clues.  It is very important, if the patient’s hemodynamic status is at all compromised (they are “symptomatic”), the WCT should be treated as VENTRICULAR TACHYCARDIA until proven otherwise.  

There have been many lists made of the ECG features that favor a diagnosis of ventricular tachycardia. Here are two such lists:  Life In The Fast Lane, and National Institute of Health.

The ECG:  This ECG shows a regular, fast, wide-QRS rhythm.  The rate is 233 bpm.  It had a sudden onset and sudden offset (not shown on this ECG), and the rhythm lasted about 3-5 minutes. The patient felt the change in rate, but did not become hypotensive or unstable.  Some features that relate directly to the most commonly-referenced VT vs. SVT charts are:

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Wide QRS Complex With First-degree AV Block

Fri, 06/07/2019 - 14:48 -- Dawn

The Patient:  This ECG was taken from a 73-year-old man with a history of heart failure with preserved ejection fraction, severe left ventricular hypertrophy, Type II diabetes, and stage 4 chronic kidney disease.  He also suffered deep vein thrombosis and is on anticoagulation.  He has a recent diagnosis of IgA myeloma.  He presented with a complaint of nausea and vomiting and was found to have a worsening of acute kidney infection.  There was suspicion of renal and cardiac amyloidosis, but the patient refused biopsy to confirm this.  He was started on chemotherapy for multiple myeloma and will be followed as an outpatient.

The ECG:  The rhythm is sinus at around 60 bpm, although the rate varies a little at the beginning of the strip.  The QRS complex is wide at .12 seconds, or 120 ms., representing interventricular conduction delay (IVCD).  The PR interval is .32 seconds, or 320 ms. This constitutes first-degree AV block.  There is left axis deviation in the frontal plane and poor R wave progression in the horizontal plane.

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Wide QRS Complex With First-degree AV Block

Fri, 06/07/2019 - 13:40 -- Dawn

The Patient:  This ECG was taken from a 73-year-old man with a history of heart failure with preserved ejection fraction, severe left ventricular hypertrophy, Type II diabetes, and stage 4 chronic kidney disease.  He also suffered deep vein thrombosis and is on anticoagulation.  He has a recent diagnosis of IgA myeloma.

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Left Bundle Branch Block

Tue, 01/17/2017 - 18:36 -- Dawn

This ECG was taken from an unknown patient.  It shows sinus tachycardia with left bundle branch block. The ECG criteria for left bundle branch block are: 

* Wide QRS (.12 seconds or greater)

* Negative QRS deflection in V1

* Positive QRS in Leads I and V6 

* Supraventricular rhythm

In addition to these criteria, left bundle branch block will cause repolarization abnormalities.  This is because depolarization is altered through the left ventricle, which causes repolarization to also be altered.  Instead of the electrical impulse traveling down the left bundle branch to depolarize the left ventricle, it depolarizes the right ventricle first, then spreads cell-to-cell across the larger left ventricle. The ST and T wave changes caused by left bundle branch block are normally “discordant”.  That is, the ST segment will be elevated in leads with negative QRS complexes, and depressed in leads with positive QRS complexes.  This elevation and depression of the ST segment may “imitate” the changes caused by acute myocardial infarction.  They may also work to conceal M.I. changes, as we may not recognize  STEMI as we attribute the ST changes to the left bundle branch block itself. 

For more on determining the presence of acute M.I. when the patient has left bundle branch block, check out these links:  ECG Guru, LBBB with AMI; Life in the Fast Lane, Sgarbossa CriteriaEMS 12-Lead, Sgarbossa Criteria;  Dr. Smith's Modified Sgarbossa Criteria. 

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AV Block With Changing PR Intervals

Wed, 09/28/2016 - 21:23 -- Dawn

Just like other subjects we are taught in school, ECG interpretation is usually taught in a very basic, simplistic way.  As we add to our knowledge, we are able to determine the mechanisms of more complex rhythms. 

When I took my first basic ECG rhythm monitoring course, I memorized all the “rules”, and at the end of the course, I thought I could read ANY strip correctly.  Then, in real life, I found that some rhythms can’t be interpreted from one lead, or even from one 12-lead ECG. 

This strip offers advanced readers to challenge themselves, and it offers teachers a chance to show students an “exception to the rules” if it is appropriate for those students.  We all learn the classification of second-degree AV blocks:  Both Type I and Type II show an underlying sinus rhythm with some P waves conducted and some not.  Type I has progressively prolonging PR intervals until a P wave is non-conducted.  The cycle restarts after the dropped QRS.  Type II has PR intervals that are all the same, and may be prolonged or normal. 

In this ECG, you will be able to “march out” a normal sinus rhythm at a rate of 80 bpm.  The P waves are marked with small dots at the bottom.  Two of every three P waves are followed by QRS complexes.  Is it Type I?  No – the PR intervals are not prolonging.  Is it Type II?  The PR intervals are not the same!  What is happening? 

There is also left bundle branch block, which is a sub-Hisian block.  Blocks occurring in the intraventricular conduction system include bundle branch blocks, second-degree AVB Type II,  and third-degree AVB with ventricular escape.  This group of blocks tends to be more threatening than the blocks that occur in the AV node (second-degree type I and third-degree with junctional escape). 

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Left Bundle Branch Block With Left Ventricular Hypertrophy

Tue, 09/20/2016 - 23:14 -- Dawn

This 92-year-old patient was diagnosed with left bundle branch block on ECG, and left ventricular hypertrophy on echocardiogram.  The two conditions are very often seen together, in fact, a majority of LBBB patients have LVH.  Since the two conditions can have similar ECG changes, it is difficult from the ECG alone to determine the presence of LVH when LBBB is present.  If the ECG criteria for LVH are present, it can be assumed that LVH is present, even in the presence of LBBB.  For determining LVH by ECG criteria, the Sokolov-Lyon criteria are commonly used ( S wave in V1 + R wave in V5 or V6 > 35 mm). 

The common criteria for left bundle branch block include:  wide QRS complex, frontal plane axis normal or leftward, negative QRS in V1, and positive QRS in leads I and V6.   LBBB is only found in supraventricular rhythms (not ventricular rhythms).  The ST segment and T wave will be negative in leads with positive QRS complexes, and positive in leads with negative QRSs (discordant).

Left ventricular hypertrophy also widens the QRS, although not often as much as LBBB does.  There will be discordant ST segments and T waves, which is called the "strain" pattern.  It also is easier to diagnose in supraventricular rhythms, because ventricular rhythms usually have large QRS complexes due to the depolarization wave being in one direction across the heart.

For confirmation of LVH, an echocardiogram is recommended.

This ECG also has an interesting rhythm.  The first beat appears normal, the second beat is a PAC.  The third beat appears to arise from a different focus, which would make it an escape beat, but it is very difficult to determine this due to the very tiny P waves.  After a pause, a regular sinus rhythm resumes.  To see the P waves, look at the right chest leads:  V1, V2, V3.  Since left bundle branch block only occurs in SUPRAVENTRICULAR rhythms, it is important to determine the rhythm, and P waves are a definite sign of SV rhythm.  We wish the P waves here were taller.

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Atrial Fib To Cardiac Arrest

Sun, 07/03/2016 - 14:31 -- Dawn

A paramedic crew responded to the office of a local physician. A 61-year-old male presented with a one-week history of chest pain and shortness of breath. He had a previously undiagnosed atrial fibrillation with rapid ventricular response and left bundle branch block, but was alert. Shortly after transport commenced, the patient became unresponsive with Torsades de Pointes, which rapidly degenerated into ventricular fibrillation. The paramedic placed pads and defibrillated within one minute.  After two minutes of compressions, the patient had a fairly regular rhythm with return of spontaneous circulation.  Transport time was short.  On catheterization, the patient was found to have severe coronary artery disease, requiring coronary artery bypass graft surgery (CABG) A balloon pump was inserted in an attempt to strengthen him for surgery.

What is the rhythm?   The 12-lead ECG presented here shows atrial fibrillation at a rate of 138 per minute.  The rhythm is irregularly-irregular with no P waves.  Since the patient had not yet been diagnosed with atrial fib, obviously no therapy had been initiated to control the rate. There is a PVC near the end of the strip.

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Left Bundle Branch Block

Tue, 02/17/2015 - 21:54 -- Dawn

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. 

 

 

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Left Bundle Branch Block and Artifact

Tue, 11/25/2014 - 20:24 -- Dawn

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

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