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6 ECG, Arrhythmia, ST and QT Monitoring
Pacemaker failure:
During complete heart block or pacemaker failure to pace/capture, tall P-waves (greater than 1/5 of
the average R-wave height) may be erroneously counted by the monitor, resulting in missed detection
of cardiac arrest.
Patients exhibiting intrinsic rhythm:
When monitoring paced patients who exhibit only intrinsic rhythm, the monitor may erroneously
count pace pulses as QRS complexes when the algorithm first encounters them, resulting in missed
detection of cardiac arrest.
The risk of missing cardiac arrest may be reduced by monitoring these patients with low heart rate limit
at or slightly above the basic/demand pacemaker rate. A low heart rate alarm alerts you when the
patient's heart rate drops to a level where pacing is needed. Proper detection and classification of the
paced rhythm can then be determined.
Filtered ECG signal from external instruments:
Instruments such as defibrillators or telemetry units produce a filtered ECG signal. When this signal is
used as an input to the bedside monitor, it is filtered again. If this twice-filtered signal is passed to the
arrhythmia algorithm, it may cause the algorithm to fail to detect pace pulses, pacemaker non-capture,
or asystole, thus compromising paced patient monitoring performance.
External pacing electrodes:
When a pacemaker with external pacing electrodes is being used on a patient, arrhythmia monitoring is
severely compromised due to the high energy level in the pacer pulse. This may result in the arrhythmia
algorithm's failure to detect pacemaker noncapture or asystole.
Fusion beat pacemakers:
Fusion beats, beats with pace pulse on top of the QRS complex, may not be detected by the monitor's
QRS detector.
Rate adaptive pacemakers:
Implanted pacemakers which can adapt to the Minute Ventilation rate may occasionally react on the
Impedance measurement used by patient monitors for the determination of the Resp value and
execute pacing with the maximum programmed rate. Switching off the Resp measurement can prevent
this.
Line isolation monitor transients:
When electrodes or lead wires are loose or detached, the monitor becomes susceptible to switching
transients from some types of line isolation monitors. Line isolation monitor transients may resemble
actual cardiac waveforms and thus inhibit heart rate alarms. To minimize the chance of this occurring,
always adhere to the instructions for skin preparation and electrode placement given in this chapter.
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