Signal-averaged electrocardiography (SAECG) is a special

electrocardiographic Electrocardiography is the process of producing an electrocardiogram (ECG or EKG), a recording of the heart's electrical activity. It is an electrogram of the heart which is a graph of voltage versus time of the electrical activity of the hea ...

technique, in which multiple electric signals from the

heart The heart is a muscular organ found in most animals. This organ pumps blood through the blood vessels of the circulatory system. The pumped blood carries oxygen and nutrients to the body, while carrying metabolic waste such as carbon diox ...

are averaged to remove

interference Interference is the act of interfering, invading, or poaching. Interference may also refer to: Communications * Interference (communication), anything which alters, modifies, or disrupts a message * Adjacent-channel interference, caused by extra ...

and reveal small variations in the

QRS complex The QRS complex is the combination of three of the graphical deflections seen on a typical electrocardiogram (ECG or EKG). It is usually the central and most visually obvious part of the tracing. It corresponds to the depolarization of the r ...

, 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 The supine position ( or ) means lying horizontally with the face and torso facing up, as opposed to the prone position, which is face down. When used in surgical procedures, it grants access to the peritoneal, thoracic and pericardial region ...

using an ECG machine equipped with SAECG software; this can be done by a

physician A physician (American English), medical practitioner (Commonwealth English), medical doctor, or simply doctor, is a health professional who practices medicine, which is concerned with promoting, maintaining or restoring health through th ...

nurse Nursing is a profession within the health care sector focused on the care of individuals, families, and communities so they may attain, maintain, or recover optimal health and quality of life. Nurses may be differentiated from other health ...

, 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 Skeletal muscles (commonly referred to as muscles) are organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other types of m ...

and to obtain a

statistically significant In statistical hypothesis testing, a result has statistical significance when it is very unlikely to have occurred given the null hypothesis (simply by chance alone). More precisely, a study's defined significance level, denoted by \alpha, is the p ...

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 (typically 1-25 uV) in the final portion of the QRS complex (the so-called "late potentials, or more accurately, "late ventricular potentials"). These can be immediately interpreted by comparing results with cut-off values.

Significance

Late potentials are taken to represent delayed and fragmented

depolarisation In biology, depolarization or hypopolarization is a change within a cell, during which the cell undergoes a shift in electric charge distribution, resulting in less negative charge inside the cell compared to the outside. Depolarization is ess ...

of the ventricular

myocardium Cardiac muscle (also called heart muscle, myocardium, cardiomyocytes and cardiac myocytes) is one of three types of vertebrate muscle tissues, with the other two being skeletal muscle and smooth muscle. It is an involuntary, striated muscle tha ...

, which may be the substrate for a micro-

re-entry Atmospheric entry is the movement of an object from outer space into and through the gases of an atmosphere of a planet, dwarf planet, or natural satellite. There are two main types of atmospheric entry: ''uncontrolled entry'', such as the entr ...

mechanism, implying a higher risk of potentially dangerous ventricular tachyarrhythmias. This has been used for the risk stratification of

sudden cardiac death Cardiac arrest is when the heart suddenly and unexpectedly stops beating. It is a medical emergency that, without immediate medical intervention, will result in sudden cardiac death within minutes. Cardiopulmonary resuscitation (CPR) and possib ...

in people who have had a

myocardial infarction A myocardial infarction (MI), commonly known as a heart attack, occurs when blood flow decreases or stops to the coronary artery of the heart, causing damage to the heart muscle. The most common symptom is chest pain or discomfort which ...

, as well as in people with known

coronary heart disease Coronary artery disease (CAD), also called coronary heart disease (CHD), ischemic heart disease (IHD), myocardial ischemia, or simply heart disease, involves Ischemia, the reduction of blood flow to the myocardium, heart muscle due to build-up o ...

cardiomyopathies Cardiomyopathy is a group of diseases that affect the heart muscle. Early on there may be few or no symptoms. As the disease worsens, shortness of breath, feeling tired, and swelling of the legs may occur, due to the onset of heart failure. A ...

, or unexplained syncope. Still, the real predictive value of these findings is questioned. Late potentials may be found in 0-10% of normal volunteers. When used as a prognostic factor for the development of

ventricular tachycardia Ventricular tachycardia (V-tach or VT) is a fast heart rate arising from the lower chambers of the heart. Although a few seconds of VT may not result in permanent problems, longer periods are dangerous; and multiple episodes over a short perio ...

, they have a

sensitivity Sensitivity may refer to: Science and technology Natural sciences * Sensitivity (physiology), the ability of an organism or organ to respond to external stimuli ** Sensory processing sensitivity in humans * Sensitivity and specificity, statisti ...

of 72% and a specificity of 75%, yielding a

positive predictive value The positive and negative predictive values (PPV and NPV respectively) are the proportions of positive and negative results in statistics and diagnostic tests that are true positive and true negative results, respectively. The PPV and NPV de ...

of 20% and a

negative predictive value The positive and negative predictive values (PPV and NPV respectively) are the proportions of positive and negative results in statistics and diagnostic tests that are true positive and true negative results, respectively. The PPV and NPV de ...

of 20%.

References

* {{PMID, 8522703 -

American College of Cardiology The American College of Cardiology (ACC), based in Washington, D.C., is a nonprofit medical association established in 1949. It bestows credentials upon cardiovascular specialists who meet its qualifications. Education is a core component of t ...

Expert Consensus Document (1996): Signal-averaged Electrocardiography, J Am Coll Cardiol. 1996 Jan;27(1):238-49. * Drew Provan and Andrew Krentz (editors), Oxford Handbook of Clinical and Laboratory Investigation,

Oxford University Press Oxford University Press (OUP) is the university press of the University of Oxford. It is the largest university press in the world, and its printing history dates back to the 1480s. Having been officially granted the legal right to print book ...

, 2003 corrected edition. Cardiac electrophysiology