Interference with function of unipolar pacemaker due to muscle potentials.

One hundred and seventy-three unipolar pulse generator systems were tested in 169 patients to determine the incidence of sensing of muscle potentials. One hundred and twenty-two implants in the pectoral region were suitable for assessment and 60 (49 per cent) demonstrated sensing. Ventricular-inhibited units sensed muscle potentials in 69 per cent (47 of 78), with 9 patients complaining of related symptoms. Ventricular-synchronous units sensed in 30 per cent (13 of 34) with no patient manifesting symptoms.