What does concordance tell us about ventricular tachycardia?
The term “concordance” has a number of uses in electrocardiography, but I want to discuss its meaning in relation to ventricular tachycardia.
First, we often use the word “positive” simply to mean that something is present. “Positive concordance” does not mean that concordance is simply “present” (though obviously it is if we are using the term). It means that ALL the precordial leads (V1 – V6) have MONOMORPHIC QRS complexes on the same side of the baseline (in this case, all MONOMORPHIC R’s). “Negative concordance” means all MONOMORPHIC QS waves. There is NO allowance for tiny q waves or tiny s waves. Nor does it mean that at least four of the leads are upright or inverted. They must ALL be MONOMORPHIC and ON THE SAME SIDE OF THE BASELINE! If not, THERE IS NO CONCORDANCE!
This is the meaning of concordance, but somewhere in our recent past authors who did not have a real understanding of what concordance actually implied began to redefine it. They applied their own “proprietary” definitions whenever the occasion suited them – mostly to be able to declare that “concordance” was present (even when it very obviously wasn’t) in order to make a diagnosis. Some said that the QRS only had to be “mostly positive or negative” in “most of the precordial leads.” One cannot move further away from the concept of concordance than that! Many website posts, journal articles and even books on electrocardiography try to relate the first step in the Brugada algorithm to determining whether concordance is present or not. The first step in the Brugada algorithm has nothing to do with concordance. If you read the original paper, the Brugadas never mention concordance – not even once!
But what does concordance – whether positive or negative – imply?
It means that there is no possibility that this represents a classic bundle branch block or aberrant conduction. Neither right nor left bundle branch block is concordant in this sense. LBBB has a negative QRS in V1 and a positive QRS in V6. RBBB has biphasic and triphasic QRS complexes throughout the precordial leads.
But take note: a basolateral accessory pathway CAN result in POSITIVE CONCORDANCE if there is antidromic conduction.
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Here are two examples of REAL positive concordance and an example of an incorrect diagnosis of negative concordance.