Concealed Conduction: Atrial Flutter
Report:
Sinus rhythm
Left atrial abnormality (LAA)
Second degree 2:1 AV block
Atrial flutter 300/min
Third degree AV block
Idioventricular escape rhythm 41/min
Inferoposterolateral MI, age uncertain, probably old
Comment:
The flutter maintains a state of refractoriness in the AV node beyond what the much slower sinus rhythm would - and abolishes AV conduction altogether. The completeness of the block associated with flutter is assessed by (i) observing the F-QRS relationship during the flutter and (ii) seeing the last idioventricular beat escape in the rhythm strip at the same cycle length as the others, regardless of the flutter stopping 0.36" earlier.
The (concealed) conduction of the flutter to the AV node is only manifest by its effect on AV nodal conduction: it is not visible per se. That is why it is called concealed.
A similar example is provided by Marriott14.
Fig 21. One block blocked by another in a 70 year old man on digoxin and quinidine.
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