WHAT IS SIGNAL-AVERAGED ELECTROCARDIOGRAPHY (SIGNAL-AVERAGED ECG, SAECG) TEST?
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 are usually associated with the 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 means the square voltage of the last 40 msec of the QRS complex, and the duration of the terminal QRS complex that measures under 40 mV.