Norm of Signal-Averaged Electrocardiography (Signal-Averaged ECG, SAECG)
No late potentials detected.
Usage of Signal-Averaged Electrocardiography (Signal-Averaged ECG, SAECG)
Determination of the risk for developing life-threatening dysrhythmias for the following high-risk conditions: myocardial infarction, clients with a history of reentrant dysrhythmias, survivors of sudden cardiac death, and syncope. Aids decision-making about the need for further evaluation and treatment, including electrophysiologic study, drug treatment, antitachycardia pacemaker, or coronary artery bypass grafting.
Description of Signal-Averaged Electrocardiography (Signal-Averaged ECG, SAECG)
Signal-averaged electrocardiography (SAECG) is an inexpensive, noninvasive method for detection of late ventricular potentials (late potentials). Late potentials are low-amplitude electrical activity occurring in diastole during a normally isoelectric phase. Their presence signals slowed conduction velocity and is usually associated with disease, ischemia, or scarring of the heart muscle. The existence of late potentials is believed to indicate a potential for the development of reentrant dysrhythmias, which may lead to sudden cardiac death. Traditional electrocardiography is not sensitive enough to detect the very-low-amplitude electrical activity of late potentials. Signal averaging is an electrocardiographic method that amplifies and averages up to 10,000 samples of electrical activity per second from the electrocardiographic signals of 100–1000 cardiac cycles to reduce the effect of random noise and artifact, thus allowing the detection of late potentials. The procedure may take up to 20 minutes, depending on the number of cardiac cycles averaged and the amount of electrical interference present. The presence of late potentials in the SAECG is determined by examination of the duration of the QRS complex, the root mean square voltage of the last 40 msec of the QRS complex, and the duration of the terminal QRS complex that measures under 40 mV.
Professional Considerations of Signal-Averaged Electrocardiography (Signal-Averaged ECG, SAECG)
Consent form NOT required.
- Provide a private, comfortable, calm, warm environment to help the client relax skeletal muscles and avoid shivering.
- To minimize artifact caused by electrical interference, turn off all nonessential electrical equipment in the area. For example, run IV pumps on battery, and turn off the hypothermia machine, television, and radio. Plug the SAECG machine into an outlet different from that of essential equipment such as a ventilator or monitor.
- Obtain electrodes, conduction gel, and an SAECG machine.
- Position the client supine or with the head of the bed slightly elevated.
- For electrode placement, clip hair from the sites, then cleanse the sites with an alcohol wipe, and scrape sites lightly with the edge of an electrode.
- Lead placement varies by institutional protocol and SAECG machine manufacturer recommendations but generally involves the placement of bipolar lead sets on the anterior and posterior areas of the torso. Apply leads according to institutional protocol.
- Follow the manufacturer's recommendations for obtaining the SAECG. This generally involves activating the SAECG machine, which runs an electrocardiographic template of the client's common cardiac cycle and then compares it to the template, amplifies it, and averages the electrical signals from a set number of subsequent cardiac cycles.
- Remove the electrodes and cleanse the skin of conductive gel.
Client and Family Teaching
- This test is performed to determine the risk of developing life-threatening dysrhythmias in high-risk conditions. This is a special kind of electrocardiogram that takes longer than a normal electrocardiogram.
- It is important to lie motionless and try to relax the muscles as much as possible throughout the procedure.
Factors That Affect Results
- Because a specific number of cardiac cycles will be averaged, the procedure will take longer than normal for clients with bradycardia and less time than normal for clients with tachycardia.
- Ectopic beats are not included in the averaging. Thus the procedure time increases for clients demonstrating a great deal of ectopy.
- Artifact is not included in the averaging. Thus movement or shivering of the client as well as electrical interference by nearby equipment will increase the procedure time.
- SAECG has not been found useful for atrial dysrhythmias, continuously irregular rhythms, or rhythms with wide QRS complexes.