User Experience Network [Health Devices Mar-Apr 1991;20(3-4):140-1]
ECG Artifact in the OR
During open-heart surgery, we often face the problem of artifact on ECGs.
The artifact is periodic and looks somewhat like QRS or pacemaker spikes. What is the
likely cause, and how can it be corrected?
In the OR, spike-like interference can be produced by two common sources:
fluid delivery systems and line isolation monitors (LIMs). In Health Devices, we
have published reports of artifact associated with fluid delivery systems, including
infusion controllers and heart-lung bypass pumps (Health Devices 7:111, Feb 1978
and 12:27, Nov 1982, respectively). Artifact has also been associated with infusion
pumps and hemodialysis machine pumps. The rate of the spikes changes as the pumping rate
is varied, and turning off the pump causes the artifact to stop. ECG artifact is caused by
the cyclic pinching and releasing of the polyvinyl chloride (PVC) tubing (or possibly
other plastic parts) in the pump, which can generate electricity through piezoelectric or
static electricity effects. The resulting electrical signal flows into the patient through
the fluid in the tubing and may be picked up by the ECG electrodes. The currents
associated with this signal pose no electrical safety risk.
Isolated power supply LIMs may also produce ECG artifact, which can occur
about once per second or at line frequency (60 Hz); recent LIM designs have greatly
reduced this problem. This source of interference can be identified by momentarily
removing the LIM fuses and looking to see whether the artifact disappears.
Although less common, electrical signals from other devices can also cause
artifact. In one case, for example, an atrial fibrillation-like artifact seen during
bronchoscopy was associated with the automatic light intensity control in a fiberoptic
light source (see Health Devices 15:24, Jan 1986).
Artifact from pumps and LIMs can be exacerbated by ECG electrode
characteristics and application, monitor performance, and environmental factors. When
experiencing such a problem, consider the following.
ECG electrodes: Discuss the problem with
your ECG electrode supplier, and verify that the most appropriate foam-backed
electrode designed for OR applications is being used. Obtain samples for trial
use from a manufacturer whose product might be superior, even if the cost is
greater, to see whether this eliminates or reduces the noise problem.
ECG electrode cables and lead wires:
Periodically inspect cables and lead wires for breaks and cracks and replace as
needed (e.g., if broken or cracked) or, primarily for lead wires,
prophylactically (e.g., weekly, monthly).
Skin preparation and application: Correct
skin preparation and electrode application are essential. Follow the electrode
manufacturer's recommendations. Generally, the only skin preparation required is
a brisk, dry rub. In "wet" procedures (i.e., chest and abdominal
surgery), it may be advisable to apply an adhesive covering over the electrode
to protect it from exposure to solutions.
Isolated power systems: Historically, the
primary purpose of an isolated power system in the OR was to reduce the fire and
explosion risks associated with the use of flammable anesthetics. As long as
only nonflammable anesthetics are used in the OR, isolated power systems are not
needed; this is consistent with national codes and standards. Thus, removing or
disabling isolated power systems that are causing noise problems is justified
(unless their use is dictated by local requirements).
Disabling these systems can be accomplished in a number of ways, including
simply grounding one side of the secondary to a suitable ground (e.g., water pipe). It is
advisable to connect each of the isolated power secondaries within one room to a single
grounding point, to identify the now "neutral" wiring at the circuit panel and
behind each outlet with a band of white tape, and to verify that all outlets are wired in
correct polarity. We also recommend replacing the explosion-proof outlets with Hospital
Grade conventional (parallel-blade) duplex receptacles.
ECG monitors: Many monitors have two
frequency-response modes (e.g., Monitor and Diagnostic). The mode with the lower
cutoff frequency (e.g., Monitor) may help reduce noise and artifact, while still
providing adequate response for monitoring applications.
The common mode rejection ratio (CMRR) is affected both by monitor design
and the ECG cable. This is not a problem with most monitors today, but CMRR can be
evaluated using the tests described in the ECG monitor acceptance testing procedures in
ECRI's Inspection and Preventive Maintenance (IPM) System.) CMRR should exceed
10,000:1 (80 dB).
Relative humidity: In one published case,
a problem of intermittent artifact was associated with cardiopulmonary bypass;
this was not resolved by the normal attention to ECG electrodes and cables.(1)
The problem occurred predominantly during the winter when the relative humidity
(RH) in the OR was low (below 50%). An aerosol spray of tap water applied to the
pump tubing in the roller heads provided partial, temporary relief, but was an
unsatisfactory solution for a number of reasons.
Users should attempt to maintain the RH near 50%, although this is not
possible in some facilities (especially older ones). (NFPA 99, 1990, Section 5-4.1.1 calls
for a RH of at least 35% and notes that several advantages have been claimed, including
avoidance of hypothermia, possible reduction in floating particulate matter, and
minimization of wound infection following procedures in ORs in which the RH is maintained
at 50% to 55%.) Adequate RH may also increase personnel comfort.
- Wald AW, Khambatta HJ, Tone JG, et al. Plastic induced ECG interference
on cardiopulmonary bypass: An adventure in clinical engineering. Clin
Eng 1990 Jul-Aug;15:301-7.
- ECG Monitors [12-599]
- Heart-Lung Bypass Units [11-969]
- Hemodialysis Units [11-969]
- Infusion Pumps, General Purpose [13-215]
- Pacemakers Cardiac [12-911]
Cause of Device-Related Incident
Device factor: Device interaction
External factor: Electromagnetic or radio-frequency interference (EMI,
Mechanism of Injury or Death
Misdiagnosis; Monitoring failure