In the setting of atrial flutter, aberrant conduction may occur when the AV block is variable. The two strips of lead V1 shown here both demonstrate atrial flutter. They are from the same patient, recorded 5 hours apart. In the upper strip, there is alternating 2:1 and 4:1 AV block. The six beats with 2:1 conduction are conducted aberrantly and demonstrate either incomplete or complete right bundle branch block. Note that the RR interval of the aberrantly conducted beats varies slightly. It is 0.4 seconds in the aberrant beats with the complete right bundle branch block and slightly longer (0.44 seconds) in the beats with incomplete right bundle branch block. The RR interval preceding each of these six aberrantly conducted beats is 0.7 seconds. In the lower strip, there is consistent 2:1 block with RR intervals of 0.4 seconds in all ventricular beats. The QRS complexes are similar and all demonstrate incomplete right bundle branch block