VEBs: Concealed Retrograde Conduction
Report:
Sinus rhythm
Left atrial abnormality
VEBs, uniform; couplets[!xe "VEBs:concealed conduction:couplets" \b \i!][!xe "VEBs:couplets" \b \i!]
Concealed retrograde conduction
Comment:
Despite a slight sinus arrhythmia it is possible to map out uninterrupted sinus P waves throughout the recordings. All the VEB couplets (except the second one in the top strip) are followed by prolonged PR intervals and corresponding shortening of the next R-R cycle.
The second couplet in the top strip blocks two P waves and replaces two sinus beats; all the others block one P wave and delay the conduction of the second one, replacing only one sinus beat. The long PR interval is due to concealed retrograde conduction of the second VEB in each couplet to the AV node. It is called concealed because its only manifestation is its effect on the subsequent beat - there is no manifest ECG evidence of the second VEB penetrating the AV node.
Since P wave generation continues uninterrupted, the P wave following the delayed one comes on time and is conducted with shorter PR interval; this leads to crowding of the two sinus QRS complexes following concealed conduction. The effect of concealed conduction may extend beyond the first PR interval, as in this case.
The commonest clinical example of concealed conduction as described above is an interpolated VEB; it just so happens that single VEBs present in this example are not interpolated, and have fully compensatory pauses.
Similar VEB couplets in trigeminy are shown below. Two P’s are blocked by each couplet.
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