Pacemaker rhythms result in classical ECG with LBBB morphology.It is a universally understood fact that RV pacing would produce LBBB and LV pacing a RBBB pattern in surface ECG.As with any other rules in medicine , it is not 100% perfect .(May be 70%)
In the process of oversimplification of rules we have forgotten a simple fact , that is, interventricular septum is shared by both the ventricles . ( functionally and electrically )
In due course , cardiologists and electrophysiologists have recognised this fact. A pacemaker lead hitching on the IVS can behave independently and disobey this golden rule of pacing.(RV-LBBB,LV-RBBB). Depending upon the orientation of the lead and the pressure it exerts on the tissue and degree of penetration of the screwing lead into the septum, the resultant ECG can either have a complete RBBB pattern , partial RBBB or partial LBBBB or combination of both.
Can RBBB pacing be stable ?
Yes., provided the the fixity of the lead and other parameters like impedance and pacing threshold are good.
Before labelling RBBB pacing as safe one should rule out pathological RBBB pacing like septal perforation and
accidental entry into LV through foremen ovale.
Is coronary sinus pacing an acceptable alternative for long term permanent pacing ?
The answer is generally ” No ” , but it needs rethinking.
A coronary sinus pacing may happen accidentally.The leads get located either in the main stem coronary sinus or it”s tributaries.the morphology of ECG depends upon the branch it enters.Leads when they reach LV aspect result in RBBB morphology.
Can we do intentional coronary sinus pacing for complete heart block ?
There are many accepted references in literature that terms RV pacing as unphysiological and has high risk of precipitating or aggravating cardiac failure. So currently , alternate sites of pacing are explored.( Septum, his bundle , biventricualr etc)
It is an irony , in this era of cardiac resynchronisation therapy where we do coronary vein pacing , the same concept is not being tried for regular permanent pacing in special and difficult situations.( Severe TR, Left sided SVC, AC canal defects etc)
Final message
- RBBB morphology following permanent pacing need not elicit a panic reaction provided all parameters are stable.
- In patients with difficult RV anatomy* , who need permanent pacemaker implantation a modified coronary sinus pacing can be a solution .But as of now no such speciifc leads are available.EP Industry should take a note on this .
*Epicardial pacing is an option in such situations .But it requires surgery.
Safe right bundle branch block pattern during permanent right ventricular pacing Journal of ElectrocardiologyJanuary 1, 2003 Yang, Yung-Nien ; Yin, Wei-Hsian ; Young, Mason Shing
Dr.S.Venkatesan MD 
I have read this article where you advice more wider application of left ventricular epicardial pacing via branches of coronary sinus. I absolutely disagree with this technique, unless defibrillator is present. The reason for this, is a fact that LV epicardial pacing results in abnormal myocardial repolarization and may cause dangerous ventricular arrhythmia. This issue even more pronounced in patients with biventricular pacing without backup ICD therapy, where both endocardial(RV) and epicardial (LV) ventricular depolarization occurs and results in heterogeneous repolarization. So I support concept of alternative site pacing, and I advice to all physicians implanting permanent pacemakers to prefer His bundle or high right ventricular septal pacing (close to the His bundle area), and implantation of biventricular pacemakers without defibrillator capability should be restricted to very selected patient population.