Unipolar electrocardiography of Wilson: A half century later

Abstract

In the October, 1935, issue of the American Heart Journal an article appeared titled, “The precordial electrocardiogram. I. The potential variations of the precordium and of the extremities in normal subjects”. 1 The paper, which described the findings in 30 normal, male medical students, received scant immediate attention, presumably because “potential variations”, an electrical term unfamiliar to most clinicians of the day, discourged reading beyond the title. If still curious enough to tackle it, the clinician soon met another formidable block to further reading when he learned that the records were said by the authors to be upside down. It was only when the term “unipolar lead”, introduced initially (1933) to describe a chest-left leg lead, 2 was later applied to precordial potentials that general clinical use of the new leads began. The relatively slow clinical acceptance of unipolar, multiple lead, precordial electrocardiography was thus at least partially ascribable to the original nomenclature used to describe it. The article, though not the first on chest leads (Waller's first human record was a chest lead 3), represented the birth of a method which has prevailed worldwide for half a century. For a laboratory procedure to be in use 50 years after its publication, in the face of the ever-increasing rate of change in diagnostic methods in clinical medicine, might be reason enough to record its hemicentennial. More compelling in this regard is the long and sometimes perilous period of gestation which preceded its birth and subsequent acceptance, a record of which discloses certain insights into the agonizingly slow pace of medical progress until a scientifically sound discovery makes previously puzzling data fit nicely together into an integrated (and in this instance) unusually practical whole. To be sure, there have been some minor modifications and several additions over the years. The ensiform lead (V E) was discarded early, and lead V 6 was substituted for it. Additional leads for specific circumstances 4 have been recommended to be made from the right anterior thorax (leads V 3R to V 5R), from the far left thorax and back (leads V 7, V 8, and V B), from higher horizontal levels (HV leads 5), and from the adbomen. 6 Arrays of numerous leads have been used for mapping of potentials of the body surface 7–9 and of the endocardium. The relatively small amplitude of the extremity potentials led to the design by Goldberger 10 of a modified central terminal to increase the size of the deflections in these leads by 50%—the augmented extremity leads (aV R, aV L, and aV F). The original traces, made in Wilson's laboratory at the University of Michigan on a two-stringin-tandem electrocardiograph built by Willem Einthoven and his son, were recorded at half-normal sensitivity (1 mV = 0.5 cm) because the two simultaneous records needed for essential measurements were too large to fit on the narrow width (10 cm) of the recording film. As it turned out later, 11 half-normal recording would have made the thoracic and extremity leads more comparable in size since the bipolar extremity leads (I, II, and III) were, on the average, about half the magnitude of the precordial leads. However, this half-normal gain was not readily accepted by clinicians, and to this day the two sets of leads are recorded at full gain (1 mV = 1 cm) except when unusually high voltages make a reduction necessary.