Aberration: seventy five years after Sir Thomas Lewis.

Seventy five years after Lewis documented aberrant intraventricular conduction, this phenomenon continues to intrigue the clinician and investigator alike. Differentiation of ventricular tachycardia and aberration with all its diagnostic and therapeutic implications is often elusive and continues to challenge the clinician and electrocardiographer. Similarly, the basic electrophysiological mechanisms responsible for the many permutations of aberration continue to attract the attention of the clinical and basic investigator. The earliest reference to abnormal intraventricular conduction of supraventricular impulses resulting from premature excitation can be found in a paper published in 1910 entitled, "Paroxysmal tachycardia, the result of ectopic impulse formation." In this paper Sir Thomas Lewis described atrial premature complexes with "three separate types of ventricular electrocardiogram." Interestingly, in the same communication, he illustrated five consecutive atrial premature complexes with the first QRS complex of the sequence, the complex preceded by the long cycle of the sinus rhythm being abnormal.' Forty eight years later, aberration dependent on a long preceding cycle became known as the Ashman phenomenon.2 In a subsequent communication, Lewis suggested that the "abnormal ventricular electrocardiograms".... "are due to disturbances of conduction in the smaller branches of this system; and it is held that definite branches are affected in this manner, though these branches cannot be identified at the present time. It is proposed that the phenomena discussed should be termed "aberration of supraventricular impulses" or simply "aberration"; the anomalous beats may be conveniently spoken of as "aberrant beats" or "aberrant ventricular contraction".3 The suggestion that abnormal intraventricular conduction is responsible