Each of the above can be important in diseased heart .The most important component seems to be Inter- ventricular synchrony .This is closely followed by AV synchrony .In dysfunctional ventricles Intra-ventricular synchrony also becomes important .In structurally normal hearts none seems to be important (This statement can be debated )
VVI pacemakers causes both AV and Inter-ventricular (VV ) dys-synchrony
DDD pacemaker may still induce Inter-ventricular ( VV ) dys-synchrony whenever RV is paced for any reason .This may happen up to 60 % of pace making time in real world.
Some more facts
*Chronic VVI pacing may induce adverse remodeling of both atria and may worsen LV dilatation. In contrast isolated chronic organic LBBB is well tolerated and with paradoxical septal motion rarely worsen the LV function.
**Please note the paradoxical septal motion , which is noted in all LBBBs is same as inter-ventricular dyssynchrony .
***Inter atrial synchrony is a less discussed issue .It becomes important in diseased atria which manifest gross intra atrial conduction blocks , atrial inhomogeneity and AF .Onset and offset of AF has a major impact in the way DDD pacing is going to fire .