Giant pacemaker spikes. An electrocardiographic artifact.

The size and orientation of the spikes produced by a pacemaker are often used by clinicians as an index of the pacemaker's function. Following implantation, the pacemaker spikes ordinarily remain constant in size; alterations suggest electrical or mechanical malfunction. We describe a patient in whom giant spikes from a pacemaker were recorded on a digital electrocardiograph shortly after implantation. An electrocardiogram taken the following day, using an analog machine, showed marked diminution in the pacemaker spike. Because of a different type of signal processing, digital electrocardiographs show much larger spikes from pacemakers than do analog machines.