[A-V conduction in atrial flutter. Electrocardiographic study]

One hundred and twenty-nine cases of atrial flutter were analyzed to assess the A-V conduction. The R-R intervals, the A-V conduction ratio, and the F-R intervals were measured in each case. Conduction in atrial flutter was defined either as constant or as variable depending on whether the A-V conduction ratio was fixed or variable. Furthermore, atrial flutter was defined as regular whenever the R-R intervals were mathematically related to each other, any interval being a multiple of the F-F cycle. On the other hand, atrial flutter was defined as irregular when the R-R cycles did not reflect a precise mathematical relationship. The R-R intervals in irregular atrial flutter were not exactly multiples of the F-F cycle. This was because the F-R intervals were variable. Sixty-five cases of atrial flutter had constant A-V conduction, whereas 64 cases were associated with variable A-V conduction. Eighty-eight per cent of cases with constant conduction were regular. On the contrary, 91% of cases with variable A-V conduction were irregular. These data reflect a relationship between the constancy of the A-V conduction ratio and the regularity of the R-R intervals. Several mechanisms were identified as being responsible for atrial flutter irregularity. Alternation of the F-R intervals was the most frequent mechanism leading to irregularity of atrial flutter with constant A-V conduction. Alternating Wenckebach periodicity was the most common cause of irregularity in atrial flutter with variable conduction ratio. Concealed conduction of blocked impulses was also frequently involved in determining atrial flutter irregularity.