[Inhibition of demand pacemakers by myopotentials and its clinical significance]

Unipolar demand pacemaker myopotential inhibition by 5 different provocative maneuvers was studied in 48 patients with stable pacing rhythm out of 82 patients with unipolar pacemakers from 3 manufacturers implanted over the right pectoralis major to evaluate the incidence of inhibiting phenomenon and its clinical significance. Transient pacing inhibition occurred in 19 (39.6%) of the 48 patients. Among them 3 (30.0%) of 10 patients with Model 28 (EDWARDS), 6 (31.6%) of 19 patients with Model 30 (EDWARDS), 10 (71.4%) of 14 patients with Model 7550 (ELAMEDICAL), and none of the 5 patients with Model P101 (QINMING). The effective maneuvers were the right hand-to-left shoulder press (63.2% positivity), the uprising from a supine position (21.0% positivity) and the hand-to-hand press (15.8% positivity). No pacemaker myopotential inhibition had been induced by Valsalva maneuver and the left hand-to-right shoulder press. 19 patients with positive myopotential inhibition had pauses of pacemaker function lasting from 1.2 to 3.9 seconds, 13 of them with pauses more than 2 seconds. Of all 48 patients, 9 (18.7%) experienced symptoms of cerebral ischemia due to pacemaker myopotential inhibition during test, among whom 8 had ventricular standstill more than 2 seconds. This showed a close relation between symptoms and duration of the pacing inhibition. The causes of the phenomenon and its prevention were briefly discussed.