Calculation of effective VV interval facilitates optimization of AV delay and VV interval in cardiac resynchronization therapy

BackgroundIn hearts with left bundle branch block (LBBB), both atrioventricular (AV) delay and interventricular (VV) interval determine left ventricular (LV) pump function in cardiac resynchronization therapy (CRT). The optimal combination of AV delay and VV interval currently is determined by extensive hemodynamic testing.ObjectivesThe purpose of this study was to investigate whether the effective VV interval (VVeff) can be used to optimize AV delay and VV interval.MethodsIn eight canine hearts with chronic LBBB, LV pacing was performed at various AV delays as well as biventricular pacing at multiple AV delays and VV intervals. LV pump function was assessed from LVdP/dtmax and stroke volume (conductance catheter). Interventricular asynchrony was calculated from the timing difference between upslope of LV and RV pressure curves. VVeff was defined as the time delay between activation of the RV apex and LV lateral wall, irrespective of the source of RV activation (RV pacing or intrinsic conduction). VVeff was determined from pacemaker settings and surface ECGs recorded during biventricular pacing at various AV delays (positive values denote LV preexcitation).ResultsFor all animals, the relationship between VVeff and LVdP/dtmax as well as LV stroke work was parabolic. Maximal improvement in LVdP/dtmax was similar during LV pacing, simultaneous biventricular pacing, and sequential biventricular pacing and was obtained at similar values of VVeff. VVeff was strongly correlated with interventricular asynchrony (R = 0.97 ± 0.03). Optimum LVdP/dtmax occurred at VVeff ranging from −24 to 12 ms (mean −6 ± 13 ms). For each experiment, the optimal VVeff was virtually equal to the value halfway between its minimum (during LV pacing at short AV delay) and maximum (during LBBB) value (R = 0.91).ConclusionUse of VVeff facilitates determination of the best combination of AV delay and VV interval during biventricular pacing. For each individual heart, VVeff, resulting in optimum LV pump function, can be estimated using surface ECGs recorded during biventricular pacing.