Atrial Flutter with Variable Block

 ECG posted to Twitter from @DanielSukmadja

 

 

Atrial Flutter with variable block. What sort of relationship is taking place between Atrium and Ventricles? My hypothesis is based on:

Multilevel Atrioventricular Block. Kosowsky, B. D., et al. Circulation, Vol 54, No 6, 1976.

 

 

The AV node (AVN) is physiologically divided into upper-level (UL) and lower-level (LL) components, each of which can influence antegrade conduction from Atrium to Ventricles.

I conceptualize it like this: 

 

Each colorized arrow is an antegrade impulse. The green impulse is blocked at the UL. The orange arrow is blocked at the LL. The black arrow successfully reaches the ventricles. Sometimes this behavior, collectively, manifests in a predictable pattern.

 

 

The alternating green and blue is to suggest that the UL has a 2:1 block. So, for every 2 impulses that enter the UL, 1 is blocked and does not proceed.

 

The alternating yellow and orange is to suggest that the LL has a 3:2 block. For every 3 impulses that enter the LL, only 2 proceed into the ventricles. Moreover, the shaded secondary impulse is to suggest that, at this level, the block is particularly Wenckebach.