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.

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. 

This is a good example of sinus rhythm with left bundle branch block.  There is some irregularity due to a PAC at the beginning.  The QRS is wide at 144 ms (.14 seconds).  There is also first-degree AV block, with a prolonged PR interval of 228 ms.  The criteria for diagnosis of left BBB are:  wide QRS, supraventricular rhythm, and a negatively-deflected QRS in V1 with a positive QRS in Leads I and V6.  

Left bundle branch block can be associated with many forms of heart disease, including CHF.  It can be permanent, transient, intermittent, or rate-related.  The wide QRS of LBBB significantly decreases cardiac output, causing poor perfusion symptoms in some people.

This ECG is a good one for your students who are just transitioning from reading rhythm strips to reading 12-lead ECGs.  It shows the value of multi-lead assessment of rhythms. You will notice that P waves are difficult to see in some leads.  Armed with the knowledge that the four channels on this ECG are run simultaneously, you can show the students how finding P waves in one lead will allow you to find them in the leads that are above and below that lead. 

Similarly, it can be difficult to see the QRS width in some leads.  The leads in the same vertical column can help you see the QRS's true width, even if part of the QRS is "flat" in the isoelectric baseline.

This is a good example of atrial fibrillation with left bundle branch block.  You get two ECGs with this one, because the patient presented to EMS with a fast heart rate, and the rate was slowed with the drug diltiazem.  We do not have any other patient information, unfortunately.

In the first strip, we see a wide-complex tachycardia.  In an emergency situation, with an unstable patient, this rhythm could safely be treated using an emergency ventricular tachycardia (VT) protocol.  In fact, all WCTs should be considered to be VT until proven otherwise.  In most emergency settings, the unstable VT patient would be electrically cardioverted, which will often convert atrial fibrillation as well.  The stable patient with this rhythm would be treated with an antiarrhythmic drug, such as amiodarone.  This may convert or slow down atrial fib.  So, in the initial stages of treatment, differentiating between VT and A Fib is not the first priority.  Assessing the patient's hemodynamic stability and addressing the rate if necessary are the priorities.  

So, how do we know this is NOT VT?  It can be difficult, but in this case, the rhythm, even though fast, is very irregular.   VT is not always perfectly regular, but this irregularly-irregular rhythm points to atrial fibrillation. Also, the pattern of the QRS morphology fits with LBBB.  The criteria for LBBB are:  1) supraventricular rhythm, 2) wide QRS, 3) negative QRS in V1 with positive QRS in Leads I and V6.  If we assume the rhythm is atrial fibrillation, we meet the first criteria.  The other two are self-evident.

After the medication is administered, 10 minutes later, we see the rate slow down.  There is no change in the irregularly-irregular rhythm, and the LBBB pattern remains.  All that has changed is the rate and, hopefully, the patient's symptoms.  This confirms that the original rhythm was not VT.  

Remember, atrial fib lowers cardiac output because there is no P wave - no "atrial kick".  Also, the fast rate associated with new-onset atrial fib often compromises ventricular filling and cardiac output.   LBBB also has a deleterious effect on cardiac output.  Wide QRS complexes indicate that the ventricles are not contracting efficiently and synchronously.  The left ventricle is depolarizing by way of a slow wave of depolarization, rather than all the cells getting the message to depolarize at the same time.  Having these two conditions at the same time can have a very negative effect on cardiac output, leading to CHF.  The first step in treatment often involves simply slowing the rate to normal, which allows for better ventricular filling and decreases the workload on the heart.  Then, the fibrillation and bundle branch block can be addressed.