Prevention of myopotential inhibition of unipolar QRS-inhibited demand pacemakers.

Seventy-two unipolar QRS-inhibited demand pacemakers were examined by provoking myopotential interference by exercise. Filter characteristics of 5 kinds of generators were tested by the use of sin wave pulse. Each myosignal of the major pectoral muscle and the abdominal rectus muscle was subjected to Fourier transform for analyses of amplitude and frequencies. Pacemaker inhibition was observed in 42 (58 per cent) of 72 with the highest frequency in the push up test. In this test, the incidence of myopotential inhibition was significantly lower (p less than 0.01) on the pacemaker implantations in the abdominal wall than that in the anterior chest wall. The myosignals of the major pectoral muscle had sufficient frequency and power density for triggering the QRS sensing mechanism but the abdominal muscular signals did not. To avoid myopotential inhibition of unipolar ventricular inhibited demand pacemakers it is most effective to implant multiprogrammable pacemakers subcutaneously in the abdominal wall and to select the optimal sensitivity according to the myopotential inhibition tests.