An 85 year old male with coronary artery disease and prior coronary stenting comes into the hospital with syncope. This EKG is obtained. Let’s learn to read it like a cardiologist. First, what do we see with the atrial rhythm? Here we have a zoomed in view of leads V1 and 2. That’s right, given we see no discernible P waves and we see these fibrillation waves, our patient is in atrial fibrillation.

Now, let’s consider the ventricular rhythm. What do you expect to see in a patient with atrial fibrillation? That’s right, normally we would see an irregularly irregular rhythm with QRS complexes coming in at varying RR intervals.  Looking back at the full 12 lead EKG for our patient, however, we see that the QRS complexes are coming at a regular rhythm of at about 40 beats per minute.

Now what does a bradycardic and regular rhythm mean for our patient in atrial fibrillation? That’s right, it implies that the patient is in complete heart block.  In complete heart block, there’s complete dissociation between what’s happening in the atria and the ventricles. Now when this happens, tissues distal to this block take over as the pacemaker for the heart.

These tissues do have an intrinsic pacemaker ability, but it’s slower than 60 beats per minute, meaning that normally they’re suppressed by the faster rate coming from the sinus node. There’s  two general locations from where this escape rhythm can come from. One is the ventricular myocytes. When a rhythm comes from the ventricular myocytes, the QRS tends to be wide with a really slow rate of  20 to 40 beats per minute and a completely abnormal QRS axis.

The second location is a location in the His Purkinje conduction system distal to the block. These rhythms tend to have a slightly  faster rate of about 40 to 60 beats per minute. The QRS is  narrow and tends to have a  normal QRS axis.  Here’s a zoomed in view of our 12 lead EKG again. What do you think? Is this a ventricular escape or a junctional escape?

Let’s go through the different aspects that we defined earlier.  Now, 40 beats per minute could be consistent with both a ventricular escape or a junctional escape. However, we see the QRS complex here is very  narrow, less than 120 milliseconds,  and we see the axis is normal, being upright in 1 and 2. So in summary, that’s right, our patient has atrial fibrillation with complete heart block and a junctional escape.

Let’s review. One, look for lack of P waves to identify atrial fibrillation. In atrial fibrillation, the QRS rhythm tends to be irregularly irregular.  If you see a regular bradycardic rhythm in the setting of atrial fibrillation, consider complete heart block.  Two, in patients with complete heart block, the escape rhythm can come from one of two general locations.

It can come from the  ventricular myocytes. This results in a  slow rate of 20 to 40 beats per minute, a  very wide QRS complex, and  a very abnormal QRS axis. It can also come from a location in the  His Purkinje system, distal to our block. This results in a  narrow QRS complex, a  normal QRS axis and rates that are slightly  faster in the 40 to 60 beats per minute range.

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85M with a history of Afib, CAD s/p PCI presents with syncope

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