User Manual

PACEMAKER PROCESSING
96 PatientNet Operator’s Manual, v1.04, 10001001-00X, Draft
All information contained herein is subject to the rights and restrictions on the title page.
Fig. 41. Three Lead Depiction of Pacemaker Rhythm
Pacemakers are electronic devices that stimulate the myocardium with an electrical
impulse. The type of pacemaker and its settings determine the frequency of the
impulse. Demand pacemakers detect the underlying heart rhythm and send an impulse
only when the heart rate falls below a preset level/rate. Fixed-rate pacemakers send an
impulse at a specific rate regardless of the intrinsic heart rate. Pacemakers are often set
to sense and stimulate the ventricle, but may also sense and stimulate the atria, or both
the atria and the ventricles (DDD or A-V sequential pacemakers). Whatever type of
pacemaker is used, there are certain characteristics that the pacemaker detection algo-
rithm looks for in order to identify a pacemaker spike. As noted earlier, when a pace-
maker spike is detected, the resulting beat is tagged or flagged. These tagged beats
activate a special algorithm to process and count the paced beats.
Because not all pacemaker spikes have the same width and amplitude, detection of the
spike and the subsequent QRS complex poses a two-fold challenge for the monitor.
The first challenge is to differentiate the pacer spike from the QRS. This is not a prob-
lem when each pacer spike is followed by an actual QRS complex. The problem arises
if the patient should go into cardiac standstill and the pacemaker continues to fire. The
monitor could count the spikes as if they were actual beats. This condition is com-
monly referred to as “dead-man” pacer. Regardless of the use of arrhythmia monitor-
ing, pacemaker patients always require additional surveillance.
The second challenge is to filter out the residual pacemaker artifact, which might trip
the QRS detector, without filtering too much of the QRS complex. The front-end
device monitor (ambulatory transceiver or bedside monitor) must detect and flag the
spike so that the residual artifact can be filtered correctly; thus allowing the algorithm
to make the appropriate response.