With the advent of cardiac resynchronization therapy (CRT), and the awareness of the impairment of ventricular systolic function caused by intraventricular conduction disorders, especially left bundle branch block, after more than 50 years of routine use, conventional right univentricular artificial cardiac pacing, particularly in its classical site – the apical region – is now being questioned. In fact, conventional right univentricular pacing usually generates a large QRS (often greater than 150 ms), with electrocardiographic pattern of left bundle branch block – more significant signs for the diagnosis of ventricular dyssynchrony that may require CRT.

Some studies have shown impairment of right univentricular pacing in patients with pacemakers compared to normal ventricular activation,^– which prompted the development of algorithms of minimal ventricular pacing, favoring exclusive atrial pacing in currently available dual-chamber pacemakers, which have shown some benefits. However, when the reestablishment of heart rate requires ventricular pacing (in cases of AV blocks), these algorithms cannot be used. Other studies have shown deterioration of ventricular systolic function after initiation of right univentricular pacing.^, In order to minimize any impairment of right univentricular pacing in cases where it is necessary, multiple pacing sites have been tried: (outflow tract, mid-septal, inferior-septal, etc.) and, although no further evidence has been achieved, today, mid-septal pacing is the most commonly method in conventional pacemaker implants, to the detriment of apical pacing.

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