aVR vs. -aVR: should aVR be left where it is?

There is a long-ranging debate regarding the proposal for replacing the frontal plane lead aVR by its inverse (–aVR), something that has already been implemented in Sweden. Technically a –aVR is not obtained by changing the lead positions, but only by creating an automated mirror of the original waveform recorded by the bipolar leads. The proponents extol the merits of this transformation of aVR,1 while others2 express reservations for such action. The debate has been further rekindled recently by the expressed intentions of some authors3 to induce cardiology societies throughout the world to adopt a switch from aVR to –aVR, and to influence the major ECG manufacturers to take steps in modifying their products for such a change. I believe that this scientific impasse can be resolved by a debate where both arguments and counterarguments about the advantages of –aVR can be heard throughout the scientific community. The recent burgeoning interest in lead aVR, in general, has succeeded in reversing its old characterization as a ‘useless lead’; aVR has some, indeed a lot, of value, based on its mathematical relationship with individual and various combinations of limb leads.4 However, the intention of this communication is not to highlight the usefulness of aVR, but to delve in the issue whether –aVR has, or does not have, advantages over aVR. The reader should keep in mind that –aVR, in the so-called orderly Cabrera sequence, is part of a general argument that expanding the 12-lead ECG more by its 12 inverse leads (e.g. –I, –aVF, –V1, –V3, etc.) constitutes a real enhancement of the ECG, in the sense that new and additional information is added.5 One, of course, could also take the view that the information stays the same, while what is added with the inverse leads is an inverse representation of the existing information.2 An additional argument is also often made that it is not that new information is imparted by –aVR, but that the created ‘symmetry’ makes for better comprehension of the ECG with important practical connotations.3 Cardiologists and others caring about ECG matters should contemplate all the arguments and counterarguments advanced on this controversy.1–3,5 Here are some arguments and counterarguments that could act as food for thought: (i) the idea of replacing aVR by –aVR leads to the aberration of introducing a negative lead among the set of all the other positive standard ECG leads, necessitating that the ECG interpreter must keep constantly in mind that that particular lead (–aVR) registers a reversed (mirror image) of what the real aVR ‘sees’ as electrical currents move away or towards it, during depolarization and repolarization, something we do not need to do for the other ‘positive’ leads. If one considers this as an advancement, we may as well expand further the ‘improvements’ by adopting –aVL, –I, –II, –aVF, and –III, so that we complete the circle in the frontal plane to 360°, instead of 150°, as recommended by others.5 (ii) The orderly sequential angular presentation of the six limb leads may have possible advantages in the ECG conceptualization; however, it deprives the ECG of a lead, i.e. aVR, strategically posed to ‘view’ the entire organ (the heart) from above, and via its upper part looking directly at the subendocardium and inside the heart, and without the interposition of muscular elements, but via the antrioventricular rings, which do not contribute electrical potentials; this has advantages in the assessment of pericarditis, subendocardial myocardial ischaemia, and subendocardial myocardial infarction. (iii) In general, availability of the current lead aVR, showing reciprocal information to what its opposite leads register, may be taken as an advantage, constituting a confirmatory insight, instead of being discussed as a disadvantage. (iv) The idea that aVR has undefined or poorly understood relationships with the other leads2 may be reversed by considering that aVR is positioned opposite the other limb leads and thus registers reciprocal information via its ‘positive’ pole, and such a view is more intuitively appealing than converting it to –aVR in the name of a ‘symmetry imperative’. (v) The notion that –aVR will retain all the specific features of aVR and, at the same time, furnish additional information and insights2 contradicts the vector-based tenet that a mirror image of a lead does not contain different or additional information to the original lead. (vi) The idea that measurements of ST and T attributes will be facilitated with the adoption of lead –aVR, and such measurements will no longer be regarded as a ‘separate entity’2 is difficult to comprehend because the results of various ECG measurements from aVR with positive or negative signs are easily conceptualized as resulting from a lead positioned opposite to the other limb leads, and from ECG complexes registered by a uniformly used positive pole for all leads, and thus the ‘different' or ‘separate’ entity becomes an advantage, i.e. a provision of a lead verifying with the positive or negative measurement values what the opposite positioned leads have registered. (vii) The notion about the possible ‘unusual’ or ‘mystical’ properties of T-waves as registered by aVR, and its clarification by using –aVR,2 is in contradiction to the above-alluded vecrorcardiographic dictum; in this respect, a negative, positive, positive/negative, or negative/positive T-wave morphology as registered by aVR can easily be reasoned by inverse-appearing reciprocal T-wave morphologies registered by leads I and II, and thus the ‘mysticism’ does not need to be invoked. (viii) This author shares the opinion about leads aVR, aVL, and aVF not being a ‘separate entity’, but part of the complete set of the six limb leads;2 however, if one wanted to ‘upgrade’ these three leads, this could be done not by merely changing their position in the way they appear in the ECG reports, but by terminating the aberration of recording the ‘augmented’ leads via the Goldberger's terminal, by adopting the Wilson's terminal for both the precordial and the ‘augmented’ leads as was done originally, and as previously recommended.6 This uniformity in recording all nine ‘unipolar’ leads is scientifically and technically appealing; besides, the reasons for proposing the ‘augmented’ leads cited originally by Goldberger, i.e. expense of using the Wilson's terminal arrangement and encumbrance of evaluating the ‘unipolar’ limb leads recorded via the Wilson's terminal stemming from the then thick ECG trace, do not apply to contemporary electrocardiography. In science, one should be open-minded to envisage as to what would happen if what he/she opposes prevails. Accordingly, one could speculate about the possible clinical and logistic impacts of reversing the aVR to –aVR. In addition to the purported, by the proponents, advantages of such an action, some possible drawbacks should be considered: (i) a confusion for some time as all the ECG machines could not be replaced at the same time. (ii) For cardiologists the change would be known and appropriately handled, but what about other physicians? (iii) The cost of buying or modifying the ECG machines may be considerable. (iv) Necessity to adopt –aVR should be implemented universally to avoid confusion. (v) Unfamiliarity in interpreting lead aVR in old hard copies or electronically archived ECGs. (vi) Unfamiliarity in interpreting lead aVR in the vast existing relevant literature. (vii) In all fairness, some of the above-cited disadvantages of a hypothetical –aVR adoption would be expected to be diminishing with the passage of time, but one should examine whether this reversal is worth the effort. We are experiencing an increasing appreciation of the diagnostic and prognostic properties of lead aVR, some known for some time, and others being currently described or investigated. These pertain to the ‘good old’ aVR, which this author feels should be left where it is; however, whether –aVR has some advantages over aVR needs to be thoroughly debated, prior to its implementation. Conflict of interest: none declared.