Myopotential Inhibition of Unipolar Pacing in Children

Myopotential inhibition of unipolar demand pacing systems has been shown to be a frequent occurrence in adults with transvenous pacing systems in which the pulse generators are implanted adjacent to the pectoralis muscle. To evaluate this problem in children, most of whom have epimyocardiol systems and abdominal wall generator implants, 50 patients underwent electrocardiographically monitored exercise nnd 24‐hour ambulatory electrocardiograph monitoring. Patients' ages at the time of study ranged from less than one year to 18 years, and weights ranged from less than 5 kg to 63 kg. Sixteen different models of pulse generators from five manufacturers were involved. Pacing modes were VVI. DVI. AAI, VDD, and DDD. Forty‐seven patients had epimyocardial systems. None of the patients was symptomatic as a result of myopotential inhibition. Oniy three patients (6%) had any evidence of myopotential inhibition and all three demonstrated this inhibition on both monitored exercise and ambulatory electrocardiograph. The inhibition was eliminated by reprogramming the sensitivity levels of the three generators without compromising R‐wave sensing. Thirteen of the remaining 35 patients with mulliprogrammable generators had induction of myopotential inhibition when exercised after temporary programming to maximal sensitivity settings. Myopotential inhibition of unipolar demand pacing appears to be less frequent and less problematic in the pediatric population, even though they are physically quite active. It is not clear whether this is a function of patient size or the abdominal wall position of the pulse generator. Because our three cases of pacing inhibition occurred in larger children, we currently recommend repeated testing for myopotential inhibition as the patients continue to grow.