signal averaged electrocardiogram (SA-ECG)
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Indications
Clinical significance
- SA-ECG detects aberrant, asynchronous electrical impulses in the 25 uV range present during sinus rhythm, called ventricular late potentials
- these signals are ordinarily obscured by skeletal muscle activity & other extraneous noises recorded in the standard ECG
- signal averaging allows for the noise to be averaged out & small consistent electrical potentials in synchrony with the QRS complex may emerge from the background noise
- SA-ECG is useful for identifying ventricular late potentials as a marker for a myocardium with slow & inhomogeneous activation from which re-entrant tachycardias originate (i.e. ventricular tachycardia)
- it is used in the setting of post myocardial infarction (MI), 7-10 days after the acute event
- an abnormal SA-ECG a few hours or days after an acute MI is generally transient
- in the time frame of 7-10 days post MI, the incidence of clinically significant arrhythmias is highest
- a normal SA-ECG post MI makes it unlikely a significant arrhythmia will occur as a result of the myocardial infarction
Limitations:
- sinus rhythm
- NO bundle branch block
- NO significant intraventricular conduction delay