Brugada’s algorithm for diagnosing ventricular tachycardia (VT)

Brugada’s algorithm is the most used algorithm for distinguishing ventricular tachycardia (VT) and supraventricular tachycardia (SVT) with wide QRS complex. The algorithm entails 5 criteria, which are tested sequentially (Figure 1).

Brugada’s algorithm

1. If there is no RS complex in any chest lead (V1–V6) a diagnosis of ventricular tachycardia can be made. Otherwise, continue to next criteria.
2. Assess the RS interval (interval from start of the R-wave to the nadir of the S-wave). If any RS interval is >100 ms and the R-wave is wider than the S-wave, a diagnosis of ventricular tachycardia can be made. Otherwise, continue to next criteria.
3. If there is AV dissociation, a diagnosis of ventricular tachycardia can be made. Otherwise, continue to next criteria.
4. Assess the QRS morphology in V1, V2, V5 and V6 (see below). If the QRS morphology is compatible with ventricular tachycardia, then the diagnosis is ventricular tachycardia.
5. If no criteria have been fulfilled, a diagnosis of supraventricular tachycardia can be made.

Judging the QRS morphology (criteria #4 in Brugada’s algorithm)

If the QRS complex in V1–V2 resembles a right bundle branch block (i.e positive QRS)

• V1:
  • Monophasic R complex suggests ventricular tachycardia.
  • qR complex suggests ventricular tachycardia.
  • if R is taller than R’, ventricular tachycardia is suggested.
  • Triphasic complexes (rSr’, rsr’, rSR’, rsR’) suggests SVT
• V6:
  • rS, QS, R or Rs complex suggests VT.

If the QRS complex in V1–V2 resembles a left bundle branch block (i.e negative QRS)

• V1:
  • The initial portion of the QRS complex is smooth in ventricular tachycardia. SVT has a sharp start of the QRS complex.
  • R-wave duration ≥40 ms suggest ventricular tachycardia.
  • Duration from start of QRS complex to nadir of S-wave ≥60 ms suggests ventricular tachycardia.
• V6:
  • QR or QS complex suggest ventricular tachycardia.
  • R or RR complex without initial q-wave suggests SVT.

All in all, Brugada’s criteria have very high sensitivity (90%) and specificity (60–90%) for diagnosing ventricular tachycardia.

Brugada’s algorithm for differentiating ventricular tachycardia from antidromic AVRT

The algorithm above frequently fails to differentiate ventricular tachycardia from antidromic AVRT. Although antidromic AVRT is an uncommon cause of ventricular tachycardia, it is important to be able to differentiate these entities. The older the patient and the more significant the heart disease, the more likely ventricular tachycardia. The Brugada group has also developed an algorithm to differentiate antidromic AVRT from ventricular tachycardia. The algorithm follows:

Brugada’s algorithm for differentiating ventricular tachycardia and antidromic AVRT

1. If the QRS complex is net negative in V4–V6, ventricular tachycardia is more likely.
2. If the QRS complex is net positive in V4–V6 and any of the leads V2–V6 display a qR complex, ventricular tachycardia is very likely.
3. If there is AV dissociation, ventricular tachycardia is very likely.
4. If there are no signs of ventricular tachycardia, antidromic AVRT should be strongly considered.