6 ECG, Arrhythmia, ST and QT Monitoring
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When using electrosurgical (ES) equipment, never place ECG electrodes near to the grounding plate of
the ES device, as this can cause a lot of interference on the ECG signal.
General:
When you are connecting the electrodes or the patient cable, make sure that the connectors never
come into contact with other conductive parts, or with earth. In particular, make sure that all of the
ECG electrodes are attached to the patient, to prevent them from contacting conductive parts or earth.
During surgery:
Use the appropriate orange electrode ECG safety cable, or lead cable with an orange connector, for
measuring ECG in the operating room. These cables have extra circuitry to protect the patient from
burns during cautery, and they decrease electrical interference. This also reduces the hazard of burns in
case of a defective neutral electrode at the HF device. These cables cannot be used for measuring
respiration.
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:
Pacemakers that create fusion beats (pace pulse on top of the QRS complex) cannot 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.
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