Pacemaker inhibition by myopotentials associated with motion and exercise.

The standard exercise tests are usually inadequate for revealing the nature of oversensing problems associated with skeletal muscle myopotentials. We used special exercises, designed to test the rectus abdominis (RA) and pectoralis major (PM) muscle groups specifically, in a study of a large number of paced patients. We examined a total of 252 paced patients, with or without symptoms and in steady pacing rhythm, for the occurrence of pacemaker inhibition (215 VVI, 15 VVI Activitrax and 22 DDD, from 9 different manufacturers). Inhibition was observed in 75 (34.9%) of the conventional VVI, in 4 (26.6%) of the VVI Activitrax and in 17 (77.3%) of the DDD paced patients. It was found that both the PM and RA were capable of causing inhibition alone in some cases, while in others a synergy of the two groups was required. It is clear that the RA must always be considered as a possible serious source of inhibiting myopotentials, irrespective of the location of the pacemaker. The most effective exercise for eliciting PM exertion was pulling the flexed arm towards the chest against resistance, while in the supine position. For RA exertion, the best exercise was raising the head and trunk from the supine position and holding the trunk at an angle of about 30 degrees to the horizontal. Both these exercises gave good, consistently reproducible results.