The pacemaker will give electrical impulses to stimulate the heart when the heart's own rate becomes slower than a set rate. Sometimes, this might result in an irregular rhythm. Rarely, if the pacemaker is in unipolar mode, there may be some stimulation of the muscle which u may feel as a twitch
If the pacemaker is programmed, any abnormal rhythms can be detected. Otherwise, if the pacemaker does not have this capacity, a Holter monitor
can be used to find out what is happening ( 24 hr ECG recording), assuming it happens at least once a day.
I hope this helps..
DR RS VARMA