We expect LBBB in RV pacing . . .but if RBBB is recorded we are worried ! (Often times it may be neither LBBB nor RBBB )
Is it really a panic situation ?
- Not necessarily. The only issue is septal perforation .It is rare , can be recognised by echo or fluro .
- In true RV apical pacing with tined leads , RBBB is extremely uncommon .
- If the lead is fixed in the septum and para hisian area , there is definite possibility of deviation from typical LBBB pattern . Screwing leads that faces high septum or outflow , RBBB can be noted occasionally.
- The commonest cause for RBBB pattern in RV pacing , is due to screw tip going deeper into septal planes and activating the fibers of left bundle early .
- For LBBB pattern to occur right bundle should be morphologically intact .In diffuse CHB with bilateral bundle branch blocks the relative contribution ( Impulse conduction ) will determine the QRS morphology . If right bundle is more damaged than left bundle ,RBBB pattern may prevail even in the midst of RV pacing !
- In elderly men with sigmoid septum typical LBBBs are not observed.
- Anther plausible mechanism would be , even though RV is paced , the pacemaker current’s exit route may be from LV side .
- Finally , always think about coronary sinus pacing .It is extremely common in blind temporary pacing.
What should we do if we encounter RBBB morphology after PPM ?
- Analyse the ECG meticulosuly for capture or sensing failure .
- Do an echocardiography in RV inflow view.
- Screen the lead by fluroscopy
- Check the pacing parameters.
- Do a holter if you are really anxious .
If everything is fine , just forget the RBBB.Don’t split your hair for this apparent paradox. In medicine impossibilities will always galore !
This paper from Taiwan would vouch for this
Dr.S.Venkatesan MD 