The pathophysiologic basis of fractionated and complex electrograms and the impact of recording techniques on their detection and interpretation.

Extracellular electrograms, recorded directly from the heart, are the hallmarks of invasive cardiac electrophysiology and provide information about the electric status of the underlying myocardium. These electrograms are generated by depolarization of cardiomyocytes that generates transmembrane currents in extracellular space and potential differences due to electric resistance of the extracellular medium. In healthy myocardium, the basic configuration of the extracellular electrogram is simple. Under pathological conditions, however, electrograms may consist of multiple components and long duration, which have been attributed to abnormal conduction and arrhythmogenicity. Although complex and fractionated electrograms are presently considered to be a real phenomenon, this was not the case some 20 years ago. Debates about the “fact or artifact” of complex and fractionated electrograms were common.1 At that time, electrograms consisting of multiple “high frequency” components with low amplitudes and long duration, termed “fractionated,” were recorded in patients with healed myocardial infarction during endocardial mapping. Several investigators presumed that fractionated electrograms were artifacts, resulting from movements between electrode and myocardium, filter characteristics of amplifiers, or represented far field effects. A classic example to support the “artifact theory” was the recording of continuous activity from the jello brain.2 In those days, much attention had been paid to fractionated electrograms in healed myocardial infarction to guide catheter ablation or antiarrhythmic surgery.3–5 Although artifacts indeed may cause complex electrograms, most of the complex and fractionated electrograms are a “fact” and caused by the peculiar behavior of activation fronts, due to structural and electric complexity of the underlying myocardium. This article delineates the origin of the unipolar extracellular electrogram, reviews the circumstances that cause fractionated and complex electrograms, and discusses the impact of the recording technique on detection and interpretation of multifaceted electrograms.