This is a tracing in taken from an 80 year old man with a Medtronic Model 8081 unipolar ventricular pacemaker. The patient had come to the clinic for a syncopal episode. During this recording the patient was doing an isometric exercise with his left arm. The monitor, in this case a Medtronic programmer, adds markers to the EKG where it detects pacer spikes. These markers look like pacemaker spikes. Spike detection is controlled by the artifact setting in the programmer, and in some cases, such as in this case, over-detect ( as in the second spike seen above). The pacemaker was set to 60/min. and clearly there is a long period of imhibition of the pacemaker by the pectoral muscle with isometric exercise. This may have been related to the patient's symptoms. The problem was corrected by decreasing the sensitivity of the pacemaker.