Patients with persistent atrial fibrillation taking oral verapamil exhibit a lower atrial frequency on the ECG.
Bollmann A, Sonne K, Esperer HD, Toepffer I, Klein HU. Patients with persistent atrial fibrillation taking oral verapamil exhibit a lower atrial frequency on the ECG. Ann Noninvasive Electrocardiol. 2002 Apr; 7(2):92-7.