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ECG Basics: Atrial Fibrillation With Complete AV Block

Tue, 05/19/2015 - 11:41 -- Dawn

This patient has an underlying atrial fibrillation with complete heart block and an idioventricular escape rhythm.  She was treated successfully with a permanent implanted pacemaker.

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The simple 5-beat rhythm strip in this case is a surprisingly effective rhythm strip for teaching a number of important principles:

  • We are told that this patient has “underlying AFib” (Atrial Fibrillation) — and now has in addition Complete AV Block. We do not have the benefit of prior tracings — nor do we have more than this 7-second rhythm strip on which to base our opinion.
  • The ECG diagnosis of AFib is based on the presence of an irregularly irregular rhythm without P waves in any of the 12 leads. Irregular undulations (ie, “fib waves”) may or may not be present in the baseline. Skeptic that I am — I do not have sufficient information to confirm the baseline diagnosis of “underlying AFib” because: i) We only have 1 unlabeled lead to look at (and P waves are sometimes present in some leads but not in others); and ii) We don’t have any baseline rhythm strip showing an irregularly irregular rhythm without P waves.
  • Clearly — it looks as if there are “fib waves” in this tracing. That said — distinction of artifact from “fib waves” is sometimes difficult without additional information …
  • The rate of the rhythm in this strip is indeed extremely slow. AFib most often presents with a rapid irregularly irregular rhythm. Presentation with a slow ventricular response may be the result of: i) overuse of rate-slowing medication; ii) recent ischemia/infarction; iii) hypothyroidism; iv) sleep apnea; v) other profound vagal stimulation; or vi) SSS ( = Sick Sinus Syndrome). Presumably the diagnosis is SSS in this example (since a permanent pacemaker was implanted) — but it is important to realize that the diagnosis of SSS can only be made after ruling out entities i)-thru-v) as potential causes of the slow ventricular response to AFib.
  • Slow AFib may be the consequence of superposition of complete AV Block on a patient with underlying AFib. This rhythm used to be seen much more often in days when Digoxin was more commonly used — but it may also occur as a result of recent ischemia/infarction — use of rate—slowing medication — Sick Sinus Syndrome — and/or some combination of these entities. That said - DID YOU NOTICE that the 3rd R-R interval in this rhythm strip is approximately 0.10 second longer than the other 3 R-R intervals? Given that we only have 5 beats on the entire tracing (and 1 of the 4 R-R intervals is different from the others!) — I would want to see MORE monitoring before concluding that this rhythm strip truly represents AFib WITH complete AV Block vs simply reflecting a very slow ventricular response to a patient with AFib.
BOTTOM LINE: Assume potentially reversible causes of the slow ventricular response have been ruled out in this case — a permanent pacemaker will likely be indicated for this patient regardless. But the point to emphasize (from a learning standpoint regarding interpretation of cardiac arrhythmias) — is that there just is not sufficient evidence from this single 5-beat tracing alone to make a definitive diagnosis of slow AFib AND complete AV Block ...
NOTE: Click HERE — for an ECG Video Review on the Basics of AV Block.

Ken Grauer, MD   [email protected] 

Submitted by Dawn on

this strip, like all "ECG BASICS" strips, is presented for the benefit of beginners and their instructors (those first learning rate and rhythm monitoring).  It is taken from a patient who was known to have atrial fibrillation who developed advanced AV block, and was felt to have an idioventricular escape rhythm. The treatment was an implanted pacemaker.  I do not remember the long-term results for this patient, because I do believe there was a lot of co-existing disease, and the patient was elderly. In the "ECG Basics" group of strips on this site, we are thinking of those who are learning to be Monitor Techs, and beginning Paramedics and Nurses. With additional education and experience, we know they will want to add knowledge of multi-lead assessment and the value of comparing previous and serial ECGs. 


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