Ventricular tachycardia (VT) is one of those “don’t-miss” ECG diagnoses because it can look deceptively similar to supraventricular rhythms—but the consequences are way higher stakes. For Step 1, you need to recognize VT quickly on an ECG, understand why it happens (usually scar + reentry), and know the management pathways (stable vs unstable; pulse vs pulseless). This post will make VT feel predictable: what it is, why it happens, how it presents, how to diagnose it, and how to treat it—plus the classic USMLE associations you’re expected to recall under pressure.
Big-Picture Definition (What VT Actually Is)
Ventricular tachycardia is a wide-complex tachycardia (usually QRS ≥ 120 ms) originating below the AV node (in the ventricles or His-Purkinje system), typically ≥ 100 bpm, often 150–250 bpm.
Key subtypes you should know
- Monomorphic VT
- QRS morphology is consistent beat-to-beat
- Classically due to reentry around a fixed scar (e.g., prior MI)
- Polymorphic VT
- QRS morphology varies beat-to-beat
- Includes torsades de pointes (when associated with prolonged QT)
Duration terminology (Step-friendly)
- Sustained VT: lasts ≥ 30 seconds or causes hemodynamic compromise requiring intervention
- Nonsustained VT: < 30 seconds, terminates spontaneously
Pathophysiology (Why VT Happens)
Think of VT as “ventricles taking over pacing,” usually because the normal conduction system is disrupted or ventricular myocardium becomes electrically unstable.
Core mechanisms
-
Reentry (most common for monomorphic VT)
- Requires:
- Circuit (often around scar tissue)
- Unidirectional block
- Slow conduction
- Classic setting: post–myocardial infarction scar → monomorphic VT
- Requires:
-
Triggered activity (afterdepolarizations)
- More relevant to torsades (early afterdepolarizations) with prolonged QT
- Can also be seen with digoxin toxicity (delayed afterdepolarizations) → ventricular ectopy/arrhythmias
-
Enhanced automaticity
- Less commonly tested, but can happen with ischemia, catecholamines, electrolyte issues
High-Yield Etiologies & Associations (USMLE Favorites)
Structural heart disease (biggest bucket)
- Prior MI → scar → monomorphic VT
- Cardiomyopathies
- Dilated cardiomyopathy
- Arrhythmogenic right ventricular cardiomyopathy (ARVC) (Step tie-in: VT in young athletes)
- Myocarditis (viral, Chagas) → ventricular arrhythmias
Ischemia (acute or chronic)
- Acute ischemia can destabilize ventricular myocardium → VT/VF
Electrolytes & drugs (especially for polymorphic VT)
- Hypokalemia
- Hypomagnesemia
- QT-prolonging drugs → torsades risk
Common Step offenders:- Class IA (quinidine, procainamide, disopyramide)
- Class III (sotalol, dofetilide, ibutilide, amiodarone can prolong QT but torsades risk is relatively lower)
- Macrolides, fluoroquinolones
- Antipsychotics (esp. typical), methadone, ondansetron
Congenital channelopathies
- Long QT syndromes (torsades)
- Brugada syndrome (VT/VF risk; coved ST elevation in V1–V3)
Clinical Presentation (What the Patient Looks Like)
VT severity depends on rate, duration, and baseline cardiac function.
Symptoms
- Palpitations
- Chest pain (ischemia demand mismatch)
- Dyspnea
- Lightheadedness/syncope (decreased cerebral perfusion)
Signs of instability (treat first, interpret later)
- Hypotension
- Altered mental status
- Shock
- Ischemic chest discomfort
- Acute heart failure/pulmonary edema
Critical Step point: VT can degenerate into ventricular fibrillation (VF) → sudden cardiac death.
ECG Diagnosis: How to Recognize VT Like a Test-Taker
Start with the Step 1 rule of thumb
Wide-complex tachycardia = VT until proven otherwise.
This is high-yield because mistreating VT as SVT with AV nodal blockers can be dangerous.
Classic ECG features
- Wide QRS (≥ 120 ms)
- Regular rhythm (often monomorphic VT)
- Rate typically 150–250 bpm
- AV dissociation (atria and ventricles doing their own thing)
- Capture beats and fusion beats (very high-yield for VT)
- Capture beat: a normal-looking narrow QRS occurs when a sinus impulse “captures” the ventricles
- Fusion beat: hybrid QRS morphology (sinus + ventricular focus simultaneously)
VT vs SVT with aberrancy (practical Step distinctions)
| Feature | VT | SVT with aberrancy |
|---|---|---|
| Age/heart disease | Often older, structural disease common | Can be younger, prior BBB |
| AV dissociation | Suggests VT | Usually absent |
| Capture/fusion beats | Strongly suggest VT | Not expected |
| Response to vagal/adenosine | Usually no termination | May terminate (if AV node dependent) |
Exam strategy: If they show a wide-complex tachycardia in someone with prior MI—pick monomorphic VT.
Classification That Drives Management: Pulse? Stable?
1) VT with a pulse
Split into stable vs unstable.
Unstable VT with pulse → synchronized cardioversion
- Unstable = hypotension, shock, ischemic chest pain, pulmonary edema, altered mental status
Stable monomorphic VT → IV antiarrhythmic
- Common Step answers: amiodarone or procainamide
- Lidocaine is classically associated with ischemic ventricular arrhythmias (more Step 1 pharm flavor)
2) Pulseless VT (treat like VF)
Pulseless VT → defibrillation (unsynchronized) + CPR
- Add epinephrine
- Then amiodarone
- This is the same algorithm bucket as VF.
Treatment: Organized, Test-Friendly Approach
Acute management algorithm (what to choose on questions)
Wide-complex tachycardia, patient unstable
- Synchronized cardioversion (if has pulse)
- Defibrillation (if pulseless)
Stable monomorphic VT
- IV amiodarone or procainamide
- Consider underlying cause: ischemia, electrolytes (K, Mg), drug toxicity
Polymorphic VT with prolonged QT (torsades)
- IV magnesium sulfate
- Stop QT-prolonging meds
- Correct K and Mg
- If unstable → defibrillation
- If recurrent/bradycardia-triggered torsades → overdrive pacing (or isoproterenol in select settings)
Step trap: Magnesium for torsades even if Mg level is “normal.”
Long-Term Management & Secondary Prevention (High Yield)
Implantable cardioverter-defibrillator (ICD)
ICDs prevent sudden death by terminating VT/VF.
High-yield indications (conceptual):
- Survivor of cardiac arrest due to VT/VF (secondary prevention)
- Sustained VT with structural heart disease (depending on EF, etiology—often Step simplifies to “ICD indicated”)
Treat the substrate
- Optimize heart failure therapy (reduces arrhythmia risk)
- Revascularize ischemia when appropriate
- Catheter ablation for recurrent monomorphic VT (often scar-related)
First Aid Cross-References (What to Revisit)
Because First Aid layout can vary by edition, use these as topic anchors to find the relevant tables/sections in your copy:
- Ventricular tachycardia & ventricular fibrillation
- Look under Cardiovascular → Arrhythmias
- Key “wide QRS tachycardia” recognition and management cues
- Antiarrhythmic drugs (Vaughan Williams)
- Class III (amiodarone, sotalol, dofetilide): K channel blockers; QT prolongation; torsades risk (esp. sotalol/dofetilide)
- Class IA (procainamide, quinidine, disopyramide): QT prolongation
- Class IB (lidocaine): ischemic ventricular arrhythmias
- Torsades de pointes
- Triggered by prolonged QT, treated with Mg
- Hyperkalemia/hypokalemia ECG changes
- Electrolytes are frequent “why did this patient go into VT?” stems
High-Yield “If You See This → Think VT” Patterns
Pattern 1: Post-MI patient with regular wide-complex tachycardia
- Diagnosis: Monomorphic VT
- Mechanism: Reentry around scar
- Treatment: stable → amiodarone/procainamide; unstable → sync cardioversion
Pattern 2: Wide-complex tachycardia + capture/fusion beats
- Diagnosis: VT
- These findings are essentially “VT stamped in neon” on Step exams.
Pattern 3: Polymorphic VT after starting a QT-prolonging drug
- Diagnosis: Torsades de pointes
- Treatment: IV magnesium + remove offending agent
Pattern 4: Pulseless “VT-looking” rhythm on monitor
- Diagnosis: Pulseless VT
- Treatment: defibrillation + CPR + epi + amiodarone
Quick Comparison Table: VT vs Torsades vs VF
| Rhythm | QRS | Regularity | Classic trigger | Key treatment |
|---|---|---|---|---|
| Monomorphic VT | Wide | Regular | Scar (post-MI), cardiomyopathy | Stable: amiodarone/procainamide; Unstable: synchronized cardioversion |
| Torsades (polymorphic VT with long QT) | Wide | “Twisting” polymorphic | Prolonged QT (drugs, low K/Mg, congenital) | IV magnesium, correct electrolytes; defib if unstable |
| Ventricular fibrillation | Chaotic | Irregular/chaotic | Ischemia, cardiomyopathy | Defibrillation + CPR |
Exam-Day Pitfalls (Avoid These)
- Assuming adenosine is always safe in wide-complex tachycardia
On exams, you’re safest treating wide-complex tachycardia as VT unless clearly proven otherwise. - Mixing up synchronized cardioversion vs defibrillation
- Synchronized for unstable tachyarrhythmia with a pulse
- Defibrillation for pulseless VT/VF
- Forgetting magnesium for torsades
- It’s the go-to answer even if labs aren’t back.
One-Sentence Takeaway
If it’s a wide-complex tachycardia, call it VT until proven otherwise, look for AV dissociation/capture/fusion beats, and treat based on stability and pulse—with magnesium for torsades and defibrillation for pulseless VT/VF.