Automatic Management of Left Ventricular Stimulation: Hints for Technologic Improvement

BACKGROUND: We used a cardiac resynchronization therapy defibrillator device with an algorithm for automatic verification of left ventricular (LV) stimulation to understand LV threshold variability, such as to provide hints to program the algorithm features. We also evaluated the algorithm performance over long term, and tested a stimulation setting to achieve 99% effective stimulation while maximizing device longevity. METHODS: The LV output was programmed as threshold + 0.5 V; the upper limit of LV output adjustment was 6 V at programmed pulse width. The algorithm is insensitive to the strength of the pacing pulse, thus pulse width was conveniently programmed to minimize the use of voltage multipliers in all the patients. Follow-ups occurred at 1 month, then every 3 months, for clinical assessment and manual threshold verification. The efficacy of this programming at long term was also evaluated by Holter validation of LV stimulation. RESULTS: Twenty patients were followed for 14 +/- 5 months (6-21). LV threshold showed no changes in 97% of consecutive days, whereas a 0.5-V and 1-V increase occurred, respectively, in 2.3% and 0.6%. Maximum variability of LV threshold was < or =0.5 V during 90% of the follow-up period. Our programming of LV output provided 99-100% effective stimulation in 18 of 20 patients, and 90% efficacy in two patients because of missed threshold measurements. A 25% increase of device longevity can be expected by this programming. CONCLUSIONS: LV threshold variability is truly modest. Daily update of LV threshold should be improved to ensure 100% LV stimulation by a threshold + 0.5 V safety margin. Device longevity is maximized when LV stimulation occurs below battery voltage.