Signal Averaged Electrocardiogram

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Introduction

• 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 infarction.
• Limitations:

• sinus rhythm
• NO bundle branch block
• NO significant intraventricular conduction delay

More General Terms

• electrocardiogram (ECG, EKG)

References

1. The Guide to Cardiology, 3rd edition, RA Kloner (editor), LeJacq communications, Greenwich Connecticut, 1995
2. Internal Medicine News 31(17): 28, 1998
3. Medical Knowledge Self Assessment Program (MKSAP) 11, American College of Physicians, Philadelphia 1998

signal averaged electrocardiogram (SA-ECG)