Unipolar Sensing Abnormalities: Incidence and Clinical Significance of Skeletal Muscle Interference and Under sensing in 228 Patients

Compared to bipolar Jead configurations, unipolar pacing systems presumably enhance sensing of cardiac electrical events but are more susceptible to electrical interference, including skeletal myopotentials The incidence and clinical significance cf oversensing and of undersensing by unipolar R‐wave inhibited pacemakers in 228 patients were assessed by 24‐hour Holter monitoring and/or by pectoral muscle exercises. Overall, 38% of patients exhibited oversensing and false inhibition due to skeletal myopotentials Symptoms due to oversensing occurred in 14% of patients and 58% of these required corrective intervention The presence of silastic coating on the pulse generator had no effect on the sensing of myopotentials In addition, the incidence of undersensing as assessed by Hoiter monitoring was 17% despite adequate implantation R wave amplitudes Thus, oversensing remains a major clinical problem when using unipolar pacemaker systems and their use has not eliminaled undersensing