Muscle Noise and Interference Behavior in Pacemakers: A Comparative Study

Inhibition of VVI pacemakers by muscle noise, though known since 1972, has attracted increased interest in recent years. More sensitive dual chamber atrial synchronized pacemakers have proved to be more susceptible to interference and will further enhance the effort at improving pacemaker resistance to interference of ail kinds. To study the reaction of 16 pacemakers of 10 different manufacturers with respect to muscle noise, we stored a noisy episode on a 16‐second endless loop tape. Each pacemaker was subjected to an identical muscle noise signal, with amplitude varied to reach the response threshold. The results are: (J) The range of muscle noise thresholds consists of more than one decade, varying from 0.4 mV to 4.6 mV. (2) Only 4 of 16 pacemakers remained unaffected if a noise signal of 3 mV maximum is assumed. (3) In 11 out of 16 pacemakers, the threshold amplitude for muscle noise is lower than that for intracardiac electrographic signals which can be explained by a sensitizing mechanism caused by noise. (4) Five pacemakers were so sensitive that even a sensitivity setting of 4 mV would not reject muscle noise. (5) Filtering muscle noise, 50‐Hz signals, and intracardiac electrograms with a 12 dB filter of variable upper cut‐off frequency revealed that heart signals are always attenuated more than interference signals.