Figure 4

A. Atrial tachycardia with 2:1 AV block due to digitalis intoxication (note diminutive P waves, barely visible even in V1)
B. Multifocal atrial tachycardia. Note the constantly changing form of ectopic P waves.

Myerburg, R.J., MD, Kessler, K.M., MD, Castellanos, A., MD, Recognition, Clinical Assessment, and Management of Arrhytmias and Conduction Disturbances, Hurst's The Heart, 8th edition, p 705-758.