chycardia. In general, left axis deviation suggests ventricular tachycardia.
QRS duration >0.14 s suggest ventricular tachycardia. QRS duration >0.16 s strongly suggest ventricular tachycardia. Note that ventricular tachycardia originating in the interventricular septum may have a relatively narrow QRS complex (0.120–0.145 s). Antidromic AVRT may also have >0.16 s. Class I antiarrhythmic drugs, tricyclic antidepressants and hyperkalemia may also cause very wide QRS complexes.
Concordance in V1–V6
Concordance means that all QRS complexes from lead V1 to lead V6 head in the same direction; all are either positive or negative. If any lead displays biphasic QRS complexes (e.g qR complex or RS complex) there cannot be concordance. Negative concordance (all QRS complexes being negative) strongly suggest ventricular tachycardia). Positive concordance (all QRS complexes being positive) are mostly due to ventricular tachycardia but may be caused by antidromic AVRT. The following figure presents concordance. To conclude, concordance is strongly suggestive of ventricular tachycardia.
Absence of RS complexes
If there is no QRS complex from lead V1 to lead V6 which is an RS complex (i.e consists of an R wave and an S wave), then ventricular tachycardia is very likely.
It is not recommended that adenosine be administered when ventricular tachycardia is suspected, because adenosine may accelerate the frequency and aggravate the arrhythmia. Occasionally adenosine is still administered (when suspecting that the arrhythmia is actually a SVT with wide QRS complexes). If adenosine do not have any effect or if it accelerates the tachycardia, it is likely to be ventricular tachycardia.
In addition to these characteristics, researchers have developed several algorithms to differentiate ventricular tachycardia from SVTs. These algorithms are briefly outlined below (refer to Management and Diagnosis of Tachyarrhythmias for details)
This is the most used algorithm. If any of the five criteria below are fulfilled, a diagnosis of ventricular tachycardia can be made.
- 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.
- 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.
- If there is AV dissociation, a diagnosis of ventricular tachycardia can be made. Otherwise, continue to next criteria.
- 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.
- 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)
- 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
- 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)
- 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.
- 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