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signal averaged electrocardiogram (SA-ECG)
Indications:
- re-entry tachycardia
- ventricular tachycardia
- post myocardial infarction
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:
1) sinus rhythm
2) NO bundle branch block
3) NO significant intraventricular conduction delay
General
electrocardiogram (ECG, EKG)
References
- The Guide to Cardiology, 3rd edition, RA Kloner (editor),
LeJacq communications, Greenwich Connecticut, 1995
- Internal Medicine News 31(17): 28, 1998
- Medical Knowledge Self Assessment Program (MKSAP) 11, American
College of Physicians, Philadelphia 1998