Inhibition of demand pacemakers by myopotentials.

The inhibition of unipolar demand pacemakers by myopotentials was studied in 215 paced patients with or without symptoms and in steady pacing rhythm. ECG recordings were taken of all patients at rest and during effort in which maximal muscular strength from the pectoralis major (PM) and rectus abdominis (RA) muscles was required. In 75 patients (34.

Rectus abdominis as a source of myopotentials inhibiting demand pacemakers.

We examined four patients with a demand pacemaker who exhibited transient symptoms of vertigo while trying to rise from the supine position. In two of these there was an epicardial pacing system with the pacemaker in the abdominal wall superficial to the rectus abdominis muscle; in the other two cases the pacing system was transvenous with the pacemaker superficial to the right pectoralis major muscle. It was found that the "pseudovertigo" was due to pacemaker inhibition caused by rectus abdominis myopotentials in all four patients.