Signal-averaged electrocardiogram
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Signal-averaged electrocardiography (SAECG) is a special electrocardiographic technique, in which multiple electric signals from the heart are averaged to remove interference and reveal small variations in the QRS complex, usually the so-called "late potentials". These may represent a predisposition towards potentially dangerous ventricular tachyarrhythmias.
Technique
Procedure
A resting electrocardiogram (ECG) is recorded in the supine position using an ECG machine equipped with SAECG software; this can be done by a physician, nurse, or medical technician. Unlike standard basal ECG recording, which requires only a few seconds, SAECG recording requires a few minutes (usually about 7-10 minutes), as the machine must record multiple subsequent QRS potentials to remove interference due to skeletal muscle and to obtain a statistically significant average trace. For this reason, it is important for the patient to lie as still as possible during the recording.
Results
SAECG recording yields a single, averaged QRS potential, usually printed in a much larger scale than standard ECGs, upon which the SAECG software performs calculations to reveal small variations in the final portion of the QRS complex (the so-called "late potentials, or more accurately, "late ventricular potentials"). These can be immediately read by comparing results with cut-off values.
Significance
Late potentials may indicate electrical instability of the ventricular myocardium and thus a propensity towards potentially dangerous ventricular tachyarrhythmias. This has been used for the sudden cardiac death risk stratification in people who have had a myocardial infarction, as well as in people with known coronary heart disease, cardiomyopathies, or unexplained syncope.
References
PMID 8522703 - American College of Cardiology Expert Consensus Document (1996): Signal-averaged Electrocardiography, J Am Coll Cardiol. 1996 Jan;27(1):238-49.