This 69-year-old woman was brought to the Emergency Department because of the recent onset of episodes of presyncope:

• Sinus rhythm with third degree AV block
• Escape wide-QRS rhythm , rate 45/min

The narrow-QRS complex at the beginning of the strip is either AV capture or an junctional escape complex with ventricular capture. The escape pacemaker is located in the right ventricle.

An electronic pacemaker was implanted:

• Electronic ventricular pacemaker (VVI)
• Sinus rhythm with complete heart block
• Paced ventricular rhythm, rate 59/min

There are sinus P waves with complete AV block. There is a single chamber ventricular pacemaker, rate 59/min.

This is a VVI pacemaker (the chamber being paced is the Ventricle, the chamber being sensed is the Ventricle, the device senses and
is Inhibited from pacing by ventricular events, such as  premature ventricular complexes). The QRS is preceded by a pacemaker spike and is typical of right ventricular pacing (wide QRS, marked left left axis deviation, Left Bundle Branch Block pattern with negative QRS in all the precordial leads).