Diagnosis of VV Delay

Normal VV Delay:
Normally, RV and LV contraction occurs almost simultaneously, i.e. the interventricular mechanical delay (IVMD) is close to zero.

VV Delay Too Long:
In VV delay with left bundle branch block, LV contracts >40-50 msec after RV

Diagnosis of VV Delay by Echocardiography:
1. Obtain pulsed wave Doppler in RVOT and LVOT.

2. Measure time-to-onset of flow (time from onset of QRS to onset of Doppler flow) in both RVOT and LVOT

3. Calculate IVMD (the difference between RVOT and LVOT time intervals). If
LVOT - RVOT time difference >40-60 msec, there is abnormal VV delay.

Timing of VV Optimization

VV Optimization: Iterative Aortic Outflow Method

1. Note that biventricular pacemakers can be programmed to excite:
   : LV first (VV delay up to +80 msec before RV)
   : LV and RV simultaneously (VV delay = 0)
   : RV first (VV delay up to -80 msec before LV)
    
2. Obtain continuous wave Doppler velocity-time integral (VTI)  of aortic valve outflow  at varying VV delays.
3. Start with VV delay of +80 msec (LV first); progressively shorten the VV delay by 20 msec until VV delay reaches -80 msec (RV first).
4. Select the VV delay at which the VTI (a proxy for LV stroke volume) is the largerst.
    

Caveats & Notes

1. RV pre-excitation (negative VV delay) should be used with caution as it may lead to decline in LV function.
2. When RV pre-excitation is used (negative VV delay), the initial AV delay obtained during monochamber LV pacing should be adjusted as follows:
   
   New AV delay = Initial AV delay - VV delay of RV pre-excitation.
    
3. In many instance VV delay of +20 msec (LV pre-excitation) is the optimal setting.

References

Barold SS, Ilercil A, Herweg B. Echocardiographic optimization of the atrioventricular and interventricular intervals during cardiac resynchronization. Europace. 2008 Nov;10 Suppl 3:iii88-95.