Tachyarrhythmias
Monomorphic ventricular tachycardia
Broad, regular, identical complexes — assume VT in any broad complex tachycardia until you have proved otherwise.
What you see
- QRS duration over 120 ms, and usually well over 140 ms.
- Every complex has the same morphology — that is what monomorphic means.
- AV dissociation, capture beats and fusion beats are diagnostic when present.
- Extreme axis deviation (northwest axis) and concordance across the chest leads favour VT.
Why it looks like that
A re-entrant circuit around a fixed scar, most often from previous infarction. Activation spreads through myocardium rather than the His–Purkinje system, so depolarisation is slow and the complex is wide.
What to do
- Unstable — shock, synchronised, without delay.
- Stable — amiodarone 300 mg IV over 20–60 minutes, then an infusion; correct potassium and magnesium.
- Look for the cause: ischaemia, electrolyte disturbance, cardiomyopathy, drugs.
- Consider an ICD for sustained VT outside the first 48 hours of an infarct or with impaired ventricular function.
The trap
Broad complex tachycardia in a patient with previous myocardial infarction is VT in over 95% of cases, whatever the blood pressure. Treating it as SVT with aberrancy and giving verapamil can precipitate arrest — haemodynamic stability is not a diagnostic criterion.
More in tachyarrhythmias
Atrial fibrillation
Irregularly irregular narrow complexes with no P waves and a wandering baseline.
Atrial flutter
Sawtooth flutter waves at about 300 per minute, usually conducted 2:1 to give a ventricular rate near 150.
AV nodal re-entrant tachycardia
Regular narrow complex tachycardia around 180 with P waves hidden inside or just after the QRS.
Torsades de pointes
Polymorphic VT twisting around the baseline, on a background of a long QT.