Wide Complex Tachycardias: Making the Brugada Criteria More User Friendly

“ECG interpretation is a process that utilizes both evidence-based science and the observational and reasoning skill of the interpreter. It is science combined with art.”
– Jerry W. Jones, MD

One of the most dreaded and intimidating decisions for any physician who reads ECGs as part of his or her daily routine involves the diagnosis of a wide complex tachycardia. Until 1991, distinguishing supraventricular tachycardia with aberrant conduction (SVT-A) from ventricular tachycardia (VT) was very difficult and stressful for the majority of physicians. Brugada et al then published their landmark approach to differential diagnosis of a regular tachycardia with a wide QRS complex.¹ Although subsequent research papers validated the importance of this original paper, none were able to achieve the same degree of sensitivity and specificity.

This has held true for every method and algorithm published to this day. While almost all have helped improve our approach to the diagnosis of wide complex tachycardias, none have been more successful than the Brugada 4-step algorithm.

It is important to note that despite the method and algorithm used, including the Brugada 4-step algorithm, you will still miss some diagnoses. You cannot and will not win them all, but overall, I have found the Brugada criteria to be the most reliable.

However, implementing the algorithm can sometimes be confusing or tedious for those who are in need of a stat decision. The problem relates to the “yes-no” approach to each step, in which “yes” diagnoses VT, and on the fourth and final step, a “no” diagnoses SVT-A by default. After reviewing their original paper many times, I felt there was an easier approach using the same criteria in each step. Please understand that my modification of the fourth step of the Brugada algorithm is not based on new evidence or new research, but is instead a rearrangement of the question that makes it simpler. We’ll review the Brugada 4-step algorithm to better understand the meaning of each step and how to make the fourth step a lot easier. But first, there are 3 things to remember before the first step:

–The Brugada 4-step algorithm applies only to wide complex tachycardias with a regular rhythm. If the rhythm is irregular, you cannot use the algorithm.

–The Brugada 4-step algorithm does not distinguish between VT and ventricular pre-excitation. An antidromic AVRT can qualify as VT using this algorithm. On the other hand, none of the other methods and algorithms reliably distinguish between them either.

–Before beginning, look at lead V1 to determine if there is a right bundle branch-like morphology or a left bundle branch-like morphology present. You are not looking for true right or left bundle branch blocks — just a morphology that resembles them. An RBBB-like morphology refers to a QRS that is mostly positive in lead V1, and an LBBB-like morphology refers to a QRS that is mostly negative in lead V1. Neither QRS has to be completely monophasic. We use only lead V1 for this determination — not lead V2 or lead V6.

The Brugada 4-Step Algorithm

1) Is there an absence of RS complexes in all precordial leads?

We begin with a confusing question for 2 reasons. First, the authors are looking for a “yes” answer to diagnose VT. Remember, a “no” answer does NOT mean the diagnosis is SVT-A until the fourth and final step. In steps 1 through 3, “no” simply means “move on to the next step.”

Second, people equate this question with deciding whether there is concordance present in the precordial leads. Concordance means that all the QRS complexes in all precordial leads are monophasic (all R waves or all QS waves) and that all are on the same side of the baseline. The word concordance is never mentioned in the Brugada paper, and they were not referring to concordance in this first step. What they discovered was that all SVT-A tracings had at least one precordial lead with an RS complex. In addition, they found that approximately 76% of all VTs also had at least one RS complex in the precordial leads. However, the most helpful aspect was that of all ECGs with no RS complexes in any of the precordial leads, 100% were tracings of VT. This goes back to the basis of step 1. Again, step 1 has nothing to do with determining the presence of concordance.

The term “RS” has several interpretations as demonstrated in the original paper: it can be an rS, RS, or Rs morphology. It is not restricted to a “large R” and a “large S.” Nor does it allow for a “q” or “Q” preceding the R (or r) wave. There are no Q’s allowed in the RS morphology.

2) Is the R to S interval >100 msec in at least one precordial lead?

Again, several things need to be clarified. First, the “R to S interval” really means from the beginning of the R wave to the nadir of the S wave. The nadir is the deepest point of the S wave. If the S wave has a prominent notch with a second nadir (Figure 1), measure the interval to the nadir of the second peak — even if it is not the deepest peak. We’re looking at duration (time) here, not voltage.

If the peak of the S wave is blunted or rounded and you cannot be certain what constitutes the “nadir,” then you cannot use that lead (Figure 2). If you cannot anwer a question with certainty, that is automatically a “no” answer — just move on to the next step.

If the R to S interval is exactly 100 msec, that is a “no” answer. Brugada et al found several examples among the ECGs they scrutinized that had an R to S interval that was exactly 100 msec. They all were found to be SVT-As. If you find such an interval, don’t be intimidated into giving it an incorrect “yes” answer.

3) Is there evidence of AV dissociation on the ECG?

This is the only step that refers to all 12 leads on the ECG. Steps 1, 2, and 4 refer to the precordial leads only. If you are seeing a wide complex tachycardia in real time with a hemodynamically stable patient in front of you, I would recommend spending no more than about 60 seconds looking for AV dissociation. The reason is this: it will only be visible in about 20% of wide complex tachycardias. And, in those cases in which it is indeed visible, it will often take the expertise and eye of a skilled ECG interpreter to see it. The slower the rate, the more likely it will be visible. But you must know what you are looking for!

The recognition of AV dissociation and VA dissociation is beyond the scope of this paper. Examples are widely available online.

4) Are the morphological criteria for VT present both in precordial leads V1-V2 and V6? (ie, present in V1 or V2 – it is not necessary to be present in both)

Here is where most of the confusion and tedium arise ­— the dreaded morphological criteria. The question is based on this statement from the original paper: “If the tachycardia fulfilled the morphology criteria for VT in leads V1 and V6, the diagnosis of VT was made.”¹

The point I want to make here is that Brugada and colleagues are looking for QRS complexes that indicate VT in both V1 and V6 — not either/or but both/and.

The classic morphologies of the bundle branch blocks in leads V1 and V6 each have a large number of non-classic variations. The original Brugada 4-step algorithm looks for each and every non-classic variation. You must do this in order to be able to answer “yes” to the question as they have posed it for step 4 in order to arrive at a diagnosis of VT.

I have changed the approach to step 4: instead of looking for all the non-classic variations, we are going to look for just the classic bundle branch block morphologies in leads V1 and V6. RBBB has just 1 classic morphology for lead V1 and 1 classic morphology for V6. LBBB has 2 classic morphologies for lead V1 and 1 classic morphology for lead V6. Thus, there are only 5 classic morphologies that you need to remember for both bundle branch blocks (Figures 3A-C).

Finally, we examine the original morphology criteria. By reducing the criteria, we will see how it makes things less complicated in our revised step 4.

RBBB-Like QRS

Lead V1

Monophasic R (Not classic RBBB pattern for V1)

QR or RS (Not classic RBBB pattern for V1)

Triphasic (rSR′) QRS complex (Classic)

Lead V6

R to S ratio <1.0 (Not classic RBBB pattern for V6)

QS or QR (Not classic RBBB pattern for V6)

Monophasic R (Not classic RBBB pattern for V6)

R to S ratio >1.0 (Does not distinguish VT from SVT-A well enough to use)

Triphasic (qRs) QRS complex (Classic)

LBBB-like QRS

Lead V1
Notching of the S wave near its nadir (Not classic LBBB pattern for V1)

Wide r wave (Not classic LBBB pattern for V1)

rS or QS complex (without notching of the S wave or widening of the r wave) (Classic)

Lead V6

R to S ratio <1.0 (Not classic LBBB pattern for V6)

QS or QR (Not classic LBBB pattern for V6)

Monophasic R (Classic)

Modification of Step 4: The Morphological Criteria

Do leads V1 and V6 both fail to show classic bundle branch block morphology?

If the answer is “yes,” you have diagnosed VT; if the answer is “no,” then the classic bundle branch block QRS complexes appear in either V1 and/or V6 and the diagnosis is SVT-A.

Final Thoughts

–If your patient is in any distress (eg, is hypotensive, diaphoretic, dyspneic, having chest pain, or has clouded sensorium), do not waste time trying to analyze the ECG. Quickly get a 12-lead ECG (if feasible) and then immediately cardiovert the patient. You can examine the ECG later, after restoring hemodynamic stability to your patient.

–If the patient is experiencing a wide complex tachycardia and (1) you are simply unable to decide on a diagnosis of the tachydysrhythmia, and (2) there is no one available to whom you could appeal for help, the safest treatment is to cardiovert the patient. If the patient is hemodynamically stable, do not assume he or she is having an aberrantly conducted supraventricular tachycardia. The most common cause of wide complex tachycardias still remains ventricular tachycardia — whether the patient is stable or not.

–Most importantly, never diagnose a tachydysrhythmia from a rhythm strip if there is any possibility of recording a 12-lead ECG. Never rely on a rhythm strip until after you have examined a 12-lead ECG! 

1. Brugada P, Brugada J, Mont L, Smeets J, Andries EW. A new approach to the differential diagnosis of a regular tachycardia with a wide QRS complex. Circulation. 1991;83(5):1649-1659. doi: 10.1161/01.cir.83.5.1649