Irregular rhythm?

The electrocardiogram recorded at presentation (Fig. 1 in the Question, 10.1007/s12471-019-1230-9) shows an atypical atrial flutter with a cycle length of approximately 300？ms. There is a remarkable variability of 2:1 to 4:1 conduction of the atrial flutter to the ventricles. This can best be explained by alternating Wenckebach periods