AV sequential pacing will present with a regular rhythm. There will be two pacer spikes: an atrial spike preceding each P wave and a ventricular spike preceding each wide QRS. The P waves typically differ from the sinus P’s. The 12-lead ECG QRS will typically show a left bundle branch block configuration with a superior axis, representing transvenous placement in the right ventricular apex.
Pacemakers are placed for a variety of reasons, but usually for symptomatic bradycardia due to AV block, or a sick sinus syndrome or a tachycardia-bradycardia syndrome. The most commonly used pacemaker is a DDD or Universal, that paces both the atria and the ventricles when needed, and preserves properly timed atrial contractions. The following animation illustrates what we have just described.