LV threshold and CRTs

Has anyone had the experience of having their LV threshold rise 2 years after receiving their CRT?
My LV threshold was initially 2.3 immediately after implantation. Then it fell to 1.75 for approximately 2 years and stayed there. So far, all of this is as it should be.
Then last summer, the LV threshold started to rise, at one point in November hitting 3.16.
Now, it appears to have settled down again and is sitting around 2.34. Still higher than the powers that be would like but somewhat better than before.
Has anyone else, who has a CRT, experienced this? What treatment, if any, was proposed to address this?