Pericardial effusion swinging heart phenomenon by dynamic radionuclide ventriculography.

asymptomatic after the unipolar lead was changed to a bipolar system. Monitoring artificial pacemaker function is an important application of ambulatory electrocardiography. Of 48 patients with suspected pacemaker malfunction reported by Iyengar et al., 24-hour monitoring detected failure in nine in whom routine examination, standard electrocardiograms, and pacemaker evaluation clinics failed to detect the malfunction.2 One type of malfunction to which unipolar demand ventricular pacemakers are vulnerable is inhibition by skeletal muscle potentials. This phenomenon, if suspected, can be provo:ked by isometric arm exercise in up to 85% of patients with unipolar lead systems.3-5 The recording of myopotential inhibition by ambulatory electrocardiography, however, has not been previously documented. We appreciated this cause of pacemaker failure in our patient, only after we more carefully inspected a Holter monitor “artifact,” originally thought to be insignificant.