Width tells you where it starts, regularity tells you which one
Expansion
| Regular | Irregular | |
|---|---|---|
| Narrow (under 120 ms) | Sinus tachycardia, AVNRT, AVRT, atrial flutter with fixed block, atrial tachycardia | Atrial fibrillation, atrial flutter with variable block, multifocal atrial tachycardia |
| Broad (over 120 ms) | Ventricular tachycardia, SVT with bundle branch block or aberrancy, antidromic AVRT | Atrial fibrillation with bundle branch block, polymorphic VT / torsades, AF with pre-excitation |
Narrow complex means the impulse reaches the ventricles through the normal conducting system, so it originates at or above the atrioventricular node. Broad complex means it does not, so it is ventricular in origin or conducted abnormally.
Features favouring ventricular tachycardia over SVT with aberrancy
- Atrioventricular dissociation, the most specific sign
- Capture and fusion beats
- Very broad QRS, over 160 ms
- Extreme axis deviation, the northwest axis
- Concordance across the chest leads, all positive or all negative
- A history of ischaemic heart disease or previous infarction, which alone makes VT far more likely than SVT
Age over 35 with a broad complex tachycardia is ventricular tachycardia in the great majority of cases, and treating it as SVT with verapamil can be fatal.
Management follows haemodynamic stability rather than the precise diagnosis: adverse features, being shock, syncope, myocardial ischaemia or heart failure, mean synchronised cardioversion. Otherwise drug treatment guided by the classification above.