Class II antiarrhythmic drugs—including such beta-adrenergic blockers as propranolol, esmolol, acebutolol, and sotalol—cause certain effects on an ECG (as shown here) by exerting particular actions on the cardiac cycle. Class II antiarrhythmics

• depress SA node automaticity
• shorten the duration of the action potential
• increase the refractory period of atrial and AV junctional tissues, which slows conduction
• inhibit sympathetic activity.