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.

Paramedic Erik Testerman has generously donated several excellent teaching ECGs to the Guru, and we will be featuring all of them soon.  This week, we show you the ECGs from a 59-year-old man with a blood glucose of 30 mg/dl.  He had no complaints .  After a bolus of Dextrose 10%, his blood glucose was 105 mg/dl.  He gave a past medical history of diabetes mellitus, hypertension, and left bundle branch block. Vitals were reported as normal and stable, except for the slow heart rate.

The first ECG, taken in the field, show a second-degree AV Block.  The conduction ratio is 2:1.  That is, there are two P waves for every QRS complex.  With this ratio, it is sometimes difficult to determine whether the patient has Type I (usually AV nodal) or Type II (Infranodal) AVB.  In order to diagnose Type I AVB (Wenckebach), we need to see TWO P waves in a row conducted, to see the prolongation of the PR interval.  It is not correct, however, to call ALL 2:1 AV blocks "Type II".  Often, simply taking a longer rhythm strip will expose a period of 3:2 conduction, showing progressive prolongation of the PRI.

This ECG, however, gives us some clues that it is probably TYPE II.  The patient has a left bundle branch block.  Type II AVBs are infranodal - that is, they affect the structures below the AV node:  the His Bundle and the Bundle Branches.  Type II AVBs represent INTERMITTENT TRI-FASCICULAR BLOCK, and that is common in the presence of RBBB  and LBBB (a bi-fascicular block).  This ECG probably represents an existing LBBB with an intermittent RBBB - When the right bundle is blocked, the patient has a tri-fascicular block, and no conduction to the ventricles.

Another clue that this is Type II is that the NON-CONDUCTED P waves fall CLEAR of the preceding T waves, meaning that they had ample opportunity to conduct, not being in the absolute refractory period.

Fortunately, the rhythm strip, taken one minute later, uncovers the diagnosis!  The sixth and seventh QRS complexes are conducted with a 3:2 ratio, showing PR intervals that stay the same, proving the rhythm is Type II. 

For this patient, the heart block and resulting bradycardia don't seem to be causing symptoms.  But infranodal blocks can easily progress to complete heart block and should be treated with implanted pacemakers.  The EMS crew in this case had transcutaneous pacer pads on the patient as a precaution, but he remained well-perfused and with a good BP the whole time. 

This ECG offers a good example of the left bundle branch block pattern.   * The QRS is wide at 144 ms.  * There is a supraventricular rhythm - in this case, normal sinus rhythm with beat number two a PAC, and a slightly prolonged PR interval.  * The QRS is negative in V1 and positive in V6 and also Lead I.  This satisfies the ECG criteria for left bundle branch block.

The main lesson this tracing offers for beginner or refresher students is the value of multi-lead assessment. Using only one or two leads, you may miss important information needed to correctly interpret the ECG.   In order to meet the LBBB criteria, we must show that there exists a supraventricular rhythm (not ventricular). One easy way to prove the rhythm is supraventricular is the presence of P waves.  In this ECG, P waves are very small, and are invisible in some leads, such as Lead I, aVL, Lead III, and aVF.  P waves can be seen well in Lead II and in the chest leads.  Some helpful hints, if viewing on a computer, enlarge the image to better see the P waves.  Look at the ECG machine's interpretation.  If a numerical PR interval is given, and a P wave axis, then the computer is finding P waves.   If you don't see them in one lead, try others.

For your more advanced students, ST elevation is common in wide-QRS rhythms, occuring in leads that have a negative QRS complex.  Conversely, ST depression will be seen in leads with wide, upright QRS complexes.  This makes the ECG with LBBB very confusing to read.  Evaluation of the ST segments should be deferred to experts.  Most EMS field protocols allow for a STEMI Alert to be called in LBBB only if the LBBB is known to be new-onset and the patient has obvious cardiac symptoms.  You can find many more examples of LBBB on this site, even LBBB with acute MI.   

 This wide complex tachycardia has an initial rate of 129/min. It is difficult to discern if P waves are present, although the ECG machine does give us a PR interval. The ECG meets most of the criteria for left bundle branch block: wide QRS, negative QRS in V1, positive QRS in Lead I and V6.The axis is leftward, which is common in LBBB.  However, it is difficult to say for certain that this is a supraventricular rhythm. Later, however, the patient's rate slowed (see top strip), revealing P waves. When the rate slowed, the left bundle branch block pattern remained. That helps confirm the original interpretation of left bundle branch block. Interestingly, the BBB is not rate-related, in that it is still present at the slower rate.

Of course, it would be helpful to have a complete 12-Lead ECG after the rate slowed, and it would also be good to see the onset and/or offset of the fast rhythm, which would help to determine if this is a sinus tachycardia or a paroxysmal supraventricular tachycardia (PSVT).  We do not have clinical data to help us determine if a sinus tachycardia with a rate of around 130 / min. would be appropriate or expected in this patient.

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