Fig. (5).

a) Complex Wenckebach with 8:3 conduction. b). Enlarged copy of lead V1 with associated ladder diagram. (a):12 lead ECG demonstrating typical atrial flutter. Note the underlying repetitive appearance of the QRS complexes with grouped beating and overall 8:3 Wenckebach block. (b) demonstrates an enlarged copy of surface lead V1 with the repeating sequence and associated ladder diagram demonstrating assumed multi-level block resulting in repeating 8:3 conduction. AVN1 and AVN2 denote 2 levels within the AV node (AVN). Note that at the first AVN level there is 2:1 block. The second AVN level demonstrates typical 4:3 Wenckebach periodicity.