Effect of Posture on LV Transvenous Lead Capture Thresholds (EXPECT)

Traditionally clinicians program the safety margins for the right atrial, right ventricular, and left ventricular leads two-times the capture thresholds. This safety margin is necessary for the right atrial and right ventricular outputs to prevent asystole during fluctuation of capture thresholds. This two-times safety margin may not be necessary for the left ventricular lead output and may be causing shorter device battery longevity. Newly implemented LV capture threshold management algorithms may help maintain a proper balance of safety margin and battery longevity. However, recent research conducted on automatic left ventricular capture measurement (LVCM) shows as much as 3.5 V daily variability in capture thresholds. In this same study, 18% of patients had >1.5 V LV threshold variability. A possible explanation for the variability of LV thresholds is lead stability. Small movements of the lead electrodes associated with movement of patient posture may account for daily fluctuation of capture thresholds. As heart failure patient care and therapies improve, CRT patients may survive longer than the projected longevities of their device. In order to minimize patient risks associated with device change-outs, care must be taken to maximize battery longevity while maintaining CRT pacing. Examining patient posture changes as a possible cause of threshold variability may guide clinicians to program more appropriate LV outputs with patient safety and device longevity in mind.