Unusual cause of desynchronization in a cardiac resynchronization device

This report describes a new cause of desynchronization encountered in a cardiac resynchronization device functioning in the VVIR mode. Left ventricular stimulation was inhibited when the sensor-driven rate exceeded the programmed left ventricular (LV) maximum trigger rate. With these devices, it is important to program the LV maximum trigger interval (essentially equivalent to a LV upper interval) to a value equal or faster than the sensor-driven upper rate.