Cardiac resynchronization using fusion promotion for timing management

An implantable medical device (IMD) configured for use as part of a cardiac therapy system comprising a leadless cardiac pacemaker (LCP) and the IMD, the IMD comprising:

• a plurality of electrodes for sensing cardiac activity;
• and
• operational circuitry configured to receive signals from the plurality of electrodes and analyze cardiac activity as follows:
• sense a QRS complex;
• and
• analyze the QRS complex to determine whether the QRS complex represents a fusion beat;
• wherein the operational circuitry is further configured to communicate to the LCP that a pacing interval change is needed to attain fusion if the QRS complex does not represent a fusion beat;
• wherein the operational circuitry is configured to analyze the QRS complex to determine whether the QRS complex represents a left ventricular (LV) paced beat and to determine whether the pacing interval change is an increase or decrease as follows:
• if the QRS complex represents an LV paced beat, determining that the pacing interval change is an increase in the pacing interval;
• or
• otherwise determining that the pacing interval change is a decrease in the pacing interval.

An implantable medical device (IMD) configured for use as part of a cardiac therapy system comprising a leadless cardiac pacemaker (LCP) and the IMD, the IMD comprising:

• a plurality of electrodes for sensing cardiac activity;
• and
• operational circuitry configured to receive signals from the plurality of electrodes and monitor cardiac electrical signals to determine whether pacing therapy issued by the LCP is causing:
• a) one or more fusion beats;
• b) one or more pace captured beats;
• or
• c) one or more intrinsic beats;
• and
• selectively communicating to the LCP to adjust pace timing if the pacing therapy is not causing one or more fusion beats.