Part of the ICU Emergencies Hub — browse every related guide in one place.
A fast rhythm with a wide QRS is a rhythm that demands respect. The single most important rule in all of tachyarrhythmia management is this: a wide-complex tachycardia is ventricular tachycardia until proven otherwise. The temptation to label it "SVT with aberrancy" and reach for adenosine or a calcium channel blocker has killed patients, because those drugs can be catastrophic if the rhythm is truly ventricular or pre-excited. This guide covers how to think about wide-complex tachycardia at the bedside, the pulse-versus-pulseless split, the stable and unstable pathways, the drugs, and the reversible causes you look for while you treat.
The overwhelming majority of wide-complex tachycardias, especially in older patients or those with any structural heart disease or prior myocardial infarction, are ventricular tachycardia. Treating VT as if it were SVT is dangerous: AV-nodal blockers like verapamil or diltiazem can cause hemodynamic collapse in VT, and adenosine given to a pre-excited (WPW) atrial fibrillation can accelerate conduction down the accessory pathway into ventricular fibrillation. Treating SVT-with-aberrancy as if it were VT, by contrast, is rarely harmful — amiodarone and cardioversion don't hurt the SVT patient. The asymmetry of risk is why the default always tips toward VT.
A wide-complex tachycardia with no pulse is not a rhythm-drug problem — it is cardiac arrest. Pulseless VT is treated exactly like ventricular fibrillation: immediate high-quality CPR and unsynchronized defibrillation, with epinephrine and amiodarone per the ACLS algorithm. A wide-complex tachycardia with a pulse gives you the stable-versus-unstable decision below. This pulse check is the fork that decides whether you are shocking synchronized or defibrillating, and it must be answered in seconds.
Monomorphic VT has a uniform, repeating QRS shape — every beat looks like the last. Polymorphic VT has a QRS that changes beat to beat; when it occurs on a background of a prolonged QT, it is torsades de pointes, which is a different treatment story (magnesium, and not the QT-prolonging antiarrhythmics). So a glance at whether the complexes are uniform or twisting steers the drug choice, which is why torsades gets its own guide.
| Drug | Role | Nursing watch-points |
|---|---|---|
| Amiodarone | First-line antiarrhythmic for stable monomorphic VT in many protocols | Give the loading infusion over the ordered time (a fast push drops BP); watch for hypotension and bradycardia |
| Procainamide | An effective alternative, favored by some for stable VT | Infuse slowly with continuous monitoring; stop if the QRS widens > 50%, the QT prolongs, hypotension develops, or the arrhythmia terminates |
| Lidocaine | An option, especially in ischemia-driven VT | Watch for neuro toxicity (confusion, tremor, seizures) with accumulation |
If the wide-complex tachycardia is causing hypotension, altered mentation, ischemic chest pain, or acute heart failure and the patient still has a pulse, the treatment is prompt synchronized cardioversion under provider direction — sedate if time and hemodynamics allow, but do not delay a truly deteriorating patient. The "sync" matters: shocking on the vulnerable part of the cardiac cycle can induce ventricular fibrillation, which is exactly why the machine is set to synchronize to the R wave. (Polymorphic VT is the exception — because the machine cannot reliably sync to a chaotic, changing QRS, an unstable polymorphic rhythm is defibrillated.)
VT rarely arises from nothing. While you treat the rhythm, the team looks for the driver: acute ischemia or infarction (the most important), low potassium and low magnesium (repleting them is both treatment and prevention), acidosis and hypoxia, a proarrhythmic drug, and a prolonged QT that would change the whole approach. A patient who is cardioverted back to sinus but left with a potassium of 2.9 and an evolving MI will be back in VT within the hour. The rhythm is the alarm; the cause is the fire.
Pair this with the torsades de pointes guide for the polymorphic exception, the synchronized cardioversion vs defibrillation guide for the shock decision, and the SVT and adenosine guide for the narrow-complex rhythm you must not confuse this with.
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