Comparison of susceptibility of myopotential inhibition between AAI and VVI pacemakers

Susceptibility of unipolar AAI pacemakers to myopotential inhibition (MPI) was assessed in 10 patients by provocative maneuvers and 24-hour Holter monitoring, and compared to that of unipolar VVI pacemakers in 12 patients. Five maneuvers were 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 less than 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 +/- 1.83 mV vs 11.20 +/- 5.95 mV (p less than 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.