Purpose:
Right ventricular pacing usually results in left bundle branch block (LBBB)-like pattern of the QRS complex or negative concordance of precordial leads. 
A right bundle branch block pattern (RBBB) appears typically during left ventricular pacing.
Recently, however, the phenomenon of right bundle branch block (RBBB) during right ventricular pacing has been described with a prevalence of up to 20% in literature.
We suspect, that a wrong positioning of ECG leads is the cause of this phenomenon.
Due to higher positioning of V₁ and V₂ , these leads do no longer provide information of the horizontal plane, but of the frontal plane.
The change of the electrical axis can lead to "wrong" RBBB.
The aim of this work was to prove that the prevalence of RBBB during right ventricular pacing is overestimated and is related to the incorrect positioning of the precordial leads V₁ and V₂.

Methods:

Patients with implanted pacemaker or defibrillator were enrolled prospectively (n=163). Six different ECGs have been recorded from every participant of the study:
Two ECGs with correct positioning of the precordial leads V₁ and V₂ in 4^th intercostal space (ICS) during intrinsic rhythm and right ventricular pacing.
Two ECGs have been recorded with high placement of leads V₁ and V₂ in 2^nd ICS.
Additionally a modern 22-leads ECG (CardioSecur) has been used. This ECG recorder generates ECGs using interpolation of vector-ECGs and were independent from precordial leads.
The ECGs were compared regarding the occurrence of RBBB during right ventricular pacing.
Furthermore, a detailed patient history with special regards on comorbidities as well as a review of x-rays for defining the device lead location has been performed.

Results:

Mc-Nemar Tests showed significant differences in frequency of RBBB during right ventricular pacing depending on the positioning the precordial leads V₁ and V₂  in 2^nd ICS versus positioning  V₁ and V₂  in 4^th ICS.
When placing the leads V₁ and V₂ in 2^nd ICS, the prevalence for RBBB was 17,2%, while the prevalence was only 1,8% when the precordial leads were positioned correctly in the 4^th ICS (p<0.001).
The prevalence for RBBB while using CardioSecur ECGs was 1,8% (p<0.001 vs 2^nd ICS).
There was no significant difference when comparing the frequency distributions of the CardioSecur ECG and the positioning in the 4^th ICS (p=1).
The likelihood for the occurrence of RBBB in the 4^th ICS was lower in patients with a non-apical device lead position compared to an apical device lead position and higher in patients with higher BMI.

Conclusion:

The positioning of precordial leads V₁ and V₂ has a significant impact on the prevalence of "false" RBBB.
The present study showed that the prevalence of RBBB during right ventricular pacing is almost zero, when the precordial leads V₁ and V₂ were positioned correctly.