Type 1 2nd degree AV block with Wenckebach periodicity and group beating may also accompany atrial tachycardias. This ECG, from a 68 year old patient, demonstrates an atrial tachycardia, probably from an ectopic focus, with a rate of 176 (the PP intervals are 036 seconds). There is group beating with a different number of QRS complexes in each group and there is progressive prolongation of the PR interval before the blocked P wave. This is best appreciated in lead II. Note that the RR intervals encompassing the pauses (0.64, 0. 66 and 0.66 seconds) are less than twice the preceding RR intervals (2 x 0.36 = 0.72 seconds).