Unipolar lead
When an unipolar LV lead is implanted, the 2 configurations that can be programmed on a CRT-P or CRT-D are the LV tip à pulse generator and the LV tip à proximal RV. With the Ilesto CRT-P or CRT-D models, the proximal RV electrode is the ring of the RV lead (proximal electrode), whereas with the new defibrillator models, the RV electrode is the coil of the RV lead (likewise for the bipolar and quadripolar configurations).
Bipolar lead
The 2 electrodes are the LV tip and ring. When a bipolar LV lead is implanted, 5 configurations can be programmed on the triple chamber defibrillators (shown on the following figure). With a CRT-P, a 6th LV ring à pulse generator configuration can be added.
Configurations available with triple chambre defibrillators
Quadripolar lead
This lead can accommodate 12 different configurations.
Automated LV threshold
Threshold measurements are based on an analysis of the evoked response, without cycle-by-cycle verification of capture. The threshold is measured once daily at a programmable time (default = 2:00 AM), beginning at a programmable amplitude (default = 3.0 V), and decreasing initially in 0.6 V, followed by 0.1 V steps. During the threshold measurement, the VV delay is programmed at 50 ms (LV preexcitation). Once LV capture has been lost, RV stimulation occurs at the end of the VV delay, to eliminate the risk of asystole in pacemaker-dependent patients.
Once the LV threshold stimulation measured, a safety margin is set for the next 24 h.
