Limb leads of the electrocardiogram - Wiley Online Library

Clin. Cardiol. 13, 346-348 (1990)

Limb Leads of the Electrocardiogram: Sequencing Revisited G . E. DOWER.M . D . . s. B. NAZZAL.M . D . . 0 . PAHLM. M . D . , * w.K. HAISTEY, JR.. M . D . . ? H. L. MARRIOTT,M . D . . $ R. H. BULLINGTON. M . D . . l D. BULLINGTON, M.D.

Department of Cardiology, Loma Linda University Medical Center, Loma Linda, California; *Department of Clinical Physiology, University of Lund, Lund. Sweden; tSection on Cardiology, Bowman-Gray School of Medicine, Winston-Salem, North Carolina: $Rogers Heart Foundation, St. Anthony’s Hospital, Florida; IPhoenix, Arizona, USA

Summary: The six limb leads are normally presented in a format the logic of which is traditional rather than anatomical and does not allow visual interpolation such as is customary with the six chest leads. The sequence: aVL, I, -aVR, 11, aVF, 111 was suggested years ago, and is used in some European countries, particularly Sweden. It provides a better impression of the extent of the changes of inferior infarction and makes the rather neglected lead aVR much more useful, though reversed in polarity. It also provides a more direct indication of the electrical axis, and simplifies comparisons with the frontal plane vectorcardiogram. Because modem digital electrocardiographs can provide the sequenced format, this seems a good time to review the advantages of adopting it.

Key words: limb leads, electrocardiogram, inferior infarction, electrical axis

Introduction The limb leads of the electrocardiogram, as they are conventionally depicted, have an inconsistent sequence and polarity. This has been recognized for many years, but there has been little tendency to change it. Several developments in recent years suggest that this is an opportune time to reconsider the issue.

Supported in part by grants from the Max and Victoria Dreyfus Foundation, New York, New York Address for reprints: S. 9. Nazzal, M.D. Department of Cardiology Lorna Linda University Medical Center Lorna Linda, CA 92354 Received: October 19, 1989 Acccpted: November 16, 1989

The I, 11, 111, aVR, aVL, aVF order of the conventional 12-lead ECG derives from the contributions of Einthoven, Wilson, and Goldberger and their colleagues. The polarity of the bipolar leads I, 11, 111 of Einthoven was chosen to give mainly positive deflections, but results in cyclically inconsistent polarity for lead 11. The polarity of the Wilson unipolar leads is consistent in that the central terminal reference is always the negative pole, but the amplitudes of the limb leads VR, VL, and VF are small relative to the bipolar leads. Goldberger “augmented” them by removing the resistors of the central terminal that shunted the signals. These aVR, aVL, aVF leads were adopted gradually; at first, they were reserved for selected cases, and did not become routine until the 1950s. Because the “standard” limb leads remained I, 11. and 111, they have routinely been given pride of place. The equilateral Einthoven triangle, which is mathematically trivial and physiologically irrelevant, has held symbolic significance, together with Einthoven’s law, which states that Lead I + Lead I1 =Lead 111. The law is merely a reflection of Einthoven’s choice of polarity (Fig. I ) , while the demonstration of that law by the geometric construction of the triangle and the electrical axis is a demonstration of a property of an equilateral triangle that has no other physical ~ignificance.~ However, the triangle gave rise to a method of displaying the limb leads characterized by the hexaxial ~ y s t e m This . ~ at once brought out the natural order of the limb leads: aVL, I, aVR, 11, aVF, 111 (Fig. 1). Note the change in the polarity of aVR. This sequence has been credited to Cabrera, but an earlier reference is Fumagalli, who originally published his recommendation in 1949.6-8Contributions by Wirth-Solereder and Case et al. should also be a c k n o ~ l e d g e d . ~ . ~ ~ It is not difficult to understand why Fumagalli’s suggestion was not taken up. First, it was overlaid with other material of less compelling interest that must have diluted the potency of the proposal. Second, electrocardiographs were hard wired so that the effect of changing the polarity of aVR could not easily be tried, though two of us (RHB and JDB) have done so. Third, the aV leads were not recorded in every case at that time, making sequenced limb leads confusing when mixed with ECGs having only

x-1

G. E. Dower et al.: Sequencing of ECG limb kdds

I

t

aVR

0

347

aVL

pictures worth a thousand words that appeared on the cover of the Journal of the Swedish Medical Association (Fig. 2).11.12

-aVR

What Are the Advantages to Changing to Sequenced Limb Leads?

aVF

FIG. I (A) Inconsistent polarity of limb leads results in Einthoven’s law: Lead I +Lead I1 =Lead 111. (B) Hexaxial order of limb leads; note sequence obtained by reversing polarity of aVR.

the standard limb lead tracings. Now, however, the situation is very different. The modem electrocardiograph is readily adapted to various configurationsby suitable software. The 12-lead ECG has itself become the standard so that the standard limb leads are never recorded alone in a diagnostic tracing. In several European countries, the sequenced display of the limb leads has already received considerable use. It has been in general use in Sweden since 1977. The success in securing the adoption of limb lead sequencing in Sweden belongs to the efforts of White and Jorfeldt, and perhaps to the appearance of one of those

FIG.2 Illustration from front cover of Journal of Swedish Medical Association, showing anatomical illogicality of the conventional order of the limb leads (courtesy of the Journal and author). Photograph by Ann-Christine Lekberg.

Perhaps the most compelling advantage is that the reader is able to gain a better impression of the extent of the changes of a recent inferior infarction. An example is given in Figure 3. The current of injury, in the sequenced display, spreads over four adjacent leads, from lead 111 to aVR. This impression of the extent of the injury is not provided by the nonsequenced display. Although aVR shows a corresponding ST depression, the significance of this would probably not be appreciated. In a limited poll, we found that most cardiologistspay little attention to aVR

FIG.3 Illustrating the value of sequencing the limb leads. The same three heart beats are represented in each tracing. In the conventional ordering of the limb leads (left), the tracings of leads 11, 111, and aVF indicate inferior infarction, whereas those of the other leads do not contribute toward this diagnosis. In the sequenced limb lead tracings (center), with the polarity of aVR reversed, it is clear that the infarction pattern is also present in the latter tracing; thus the extent of the infarction is more apparent. (From Ref. 13)

348

Clin. Cardiol. Vol. 13. May 1990

when interpreting the 12-lead ECG. Goldberger's suggestion that the presence or absence of a n initial R in aVR permits separation o f positive and positional Q waves in inferior leads might have received more attention had it related to a Q wave in aVR.I2 When interpreting the precordial leads, readers tend to interpolate between patterns in adjacent leads to gain a general picture o f precordial changes. They use this approach when comparing seria1 tracings with one another, thereby allowing for inconsistencies in the placement of the precordial electrodes. Although the placement of limb electrodes is more consistent, positional changes between consecutive tracings can occur, sometimes due to the position of the left shoulder with respect to the trunk.13 If the limb lead tracings are sequenced, it becomes possible to cany out interpolations similar to those described for the precordial leads. For example, whereas the tracings seen in a V F may look rather different in serial tracings, sequencing may show that 'the difference is due to a resemblence toward the lead 111 tracing in one tracing and the lead I1 tracing in another. It is interesting that sequencing of the limb leads appears in several figures in a recent definitive text on electrocardiography, and is required in c e m i n displays of trend over time.14.15 W e hope that, by bringing together various points in favor of what is, after all, a simple change, adoption of this useful display will receive more favorable consideration in North America.

Concluding Remarks Some changes, like converting to the metric system or improving the typewriter keyboard, are clearly sensible but involve too big a change in our way of doing things for them to be readily adopted. Others, like reform of the calendar, involve scarcely any mental effort to adopt but general inertia makes them unlikely. The adoption o f a sequenced system for presenting the limb leads, although at one time difficult to implement because it involved modification of equipment, can now be adopted very easily. The change in our habit of interpretation is so minor that it takes but an hour to adjust to the new format. We

would not say it is a change that is long overdue so much as a change whose time has come because present technology now makes it easy. The results of the change are subtle rather than striking, but the intuition it provides tends to influence the way in which we picture the electrical forces in the ECG.

References I . Einthoven W , Fahr GE, DeWaart A: On the direction and manifest size of the variations of potential in the human heart and on the influence of the position of the heart on the form of the electrocardiogram (translation). Am Heart J 40. 163 (1950) 2. Wilson FN, Johnston FD, MacLeod AG, Barker PS: Electrocardiograms that represent the potential variations of a single electrode. Am Heart J 9, 447 (1934) 3. Goldberger E: A simple, indifferent, electmardiographic electrode of zero potential and technique of obtaining augmented, unipolar, extremity leads. Am Heart J 23, 483 (1942) 4. Dower GE: Polurcurdiogruphy. Charles C Thomas, Springfield, IL (1971) 282 5 . Sodi-Pellares D, Cuellar A, Cabrera E: Siztema de seis ejes con aplicacion a1 vector A T en las hipertrofias ventriculares. Arch Inst Curdiol Mexico 14, 142 (1944-5) 6. Cabrera E: Electmcanliographie Clinique: Theorie et Pratique. Masson, Paris (1959) 7. Fumagalli B: Unipolar value of standard limb lead -aVR and rational arrangement of limb leads. Am Heurr J 48,204 ( 1954) 8. Fumagalli B: Interpretation unipolare de I'electrocardiogramme piripherique. Arch Mu1 Coeur 42, 891 (1949) 9. Wirth-Soleder R: Untersuchungsmethoden in der Elektrokardiographie und ihre Beurteilung. Internist Prux 3, 293 (1963) 10. Case RB, Tansey WA, Mogtader MD: A sequential angular lead presentation. J Electrocurdiol 12, 395 (1979) I 1. White TL: Ordningsfoljden for extremitets-avledningama i EKG. Lrrkurtidningen 68, 1352 ( I97 I ) 12. Jorfeldt L: Standardisering av EKG-avledningar. Lrrkurtidningen 72, 4497 (1975) 13. Dower GE, Machado HB, Osborne JA: On deriving the electrocardiogram from vectorcardiographic leads. Clin Curdid 3, 87 (1980) 14. MacFarlane PW. Lawrie TDV: Coniprchensive Electrocurdiology. Pergamon, New York (1989) 439, 440, 445 15. Krucoff MW, Pope JE, Bottner RK, Renzi RH, Wagner GS, Kent KM: Computer-assisted ST segment monitoring: Experience during and after brief coronary occlusion. ./ Electrcicurdiol 20 (suppl) (1989) 15, 87