AAI pacemakers are currently used for the treatment of bradyar- rhythmias without atrioventricular conduction disturbances. Oversensing of myopotentials may occur in unipolar AAI as well as in unipolar VVI pace-

performed for each of four different sensitivity levels, and an MPI score of from 0-4 points was given according to the lowest sensitivity level at which MPI was provoked. The MPI score in patients with AAI pacemakers was significantly lower than that in patients with VVI pacemakers, 1.60•}1.26 vs 2.83•}1.03 (p<0.05). On Holter monitoring, no MPI was detected in any of the patients with AAI pacemakers, whereas myopotential inhibition was detected in 5/12 patients (42%) with VVI pacemakers. Intracardiac electrograms were of lower amplitudes for AAI pacing than for VVI pacing, 3.13•}1.83mV vs 11.20•}5.95mV (p<0.01). Although the amplitude of atrial signals was lower than that of ventricular signals, the AAI pacemakers were less susceptible to MPI than were the VVI pacemakers. However, when MPI occurs in AAI pacing, it may be more difficult to correct without undersensing because of the lower amplitude of the intracardiac signals.