Myopotential inhibition of unipolar ventricular inhibited pacemakers: prevention by an insulating sheath.

To determine the occurrence of inhibition of pacing by sensing of myopotentials, forty-five patients with predominant pacemaker driven heart rhythm were studied. In eleven patients with a bipolar lead system myopotential inhibition was never observed. In the remaining group (34 patients) with unipolar pacemakers myopotential inhibition was demonstrated in fifteen patients. Three of them were symptomatic, two severely. In forty new implants a silicone-rubber insulating sheath was placed against the muscular side of the pacemaker. In none of these patients myopotential inhibition could be demonstrated. The authors conclude that myopotential inhibition occurs frequently in unipolar ventricular inhibited pacemakers, and can be prevented by insulating the muscular side of the anodal surface.