Polymorphic ventricular tachycardia

Background

• Form of ventricular tachycardia
  • Multiple ventricular foci
  • QRS complexes with varying morphology
• Subtypes include:
  • Torsades de pointes
  • bidirectional polymorphic VTach (as seen in digoxin toxicity)

Etiologies

• Myocardial ischemia (most common)
• Acquired or congenital prolonged QT
  • TCAs, phenothiazines, Type I antiarrhythmics (quinidine, procainamide)
  • Hypokalemia
  • Hypomagnesemia
  • Elevated intracranial pressure
• Brugada syndrome, short QT syndrome, congenital catecholaminergic polymorphic ventricular tachycardia

Clinical Features

• Syncope
• Palpitations
• Altered level of consciousness
• May present with cardiac arrest

Differential Diagnosis

Wide-complex tachycardia

Assume any wide-complex tachycardia is ventricular tachycardia until proven otherwise (it is safer to incorrectly assume a ventricular dysrhythmia than supraventricular tachycardia with abberancy)

• Regular
  • Monomorphic ventricular tachycardia
  • PSVT with aberrant conduction:
    • PSVT with bundle branch block^
    • PSVT with accessory pathway
    • Atrial flutter with bundle branch block^
  • Sinus tachycardia with bundle branch block^
  • Accelerated idioventricular rhythm (consider if less than or ~120 bpm)
  • Metabolic
    • Hyperkalemia
    • Digoxin toxicity
    • Severe metabolic acidosis
• Irregular
  • Atrial fibrillation/atrial flutter with variable AV conduction AND bundle branch block^
  • Atrial fibrillation/atrial flutter with variable AV conduction AND accessory pathway (e.g. WPW)
  • Atrial fibrillation + hyperkalemia
  • Polymorphic ventricular tachycardia
    • Torsades de pointes
    • Nonsustained ventricular tachycardia

^Fixed or rate-related

Evaluation

Torsades de Pointes in a rhythm strip.

• Evaluate for underlying causes (e.g. electrolyte imbalances, ACS)

ECG Findings

• Wide QRS (>100ms or 3 small boxes)
• QRS complexes of varied amplitude, axis and duration
  • Torsades: QRS complexes appear to twist around isoelectric line
• Rapid rhythm (usually 140-160 bpm, but can be up to 300 bpm)
• Irregular

Management

Pulseless

See Adult pulseless arrest and Pediatric pulseless arrest

Unstable

• Unsynchronized cardioversion (defibrillation) 200J (or 2J/kg for pediatrics)
• Correct any electrolyte abnormalities

Stable

• Correct any electrolyte abnormalities
• Torsades:
  • Magnesium sulfate (for Torsades):
    • 1-2gm IV, repeat in 5-15min; then 1-2gm/hr (3-10mg/min) drip
    • Peds: 25-50mg/kg (max 2g) IV
  • Isoproterenol, 2-8 mcg/min (if available)
  • Overdrive Pacing to goal HR 90-120
    • Note that this is only effective for preventing recurrence of TdP - it will not convert TdP to sinus rhythm
  • Consider Lidocaine
  • Avoid procainamide, amiodarone (may further prolong QT)
• Non-Torsades (baseline QT interval not prolonged)
  • Amiodarone, agent of choice in setting of AMI or LV dysfunction
    • 150 mg over 10min (15 mg/min), followed by 1 mg/min drip over 6hrs (360 mg total), then 0.5 mg/min drip over next 18 hrs (540 mg total)
    • Peds: 5mg/kg (max 300mg), may repeat twice
  • Procainamide
    • 100 mg q5min until termination of arrhythmia, then start 2-6 mg/min (or 1-2 mg/min for renal/cardiac failure)
    • Max dose 17mg/kg OR widening of QRS >50%
  • Lidocaine, 1-1.5mg/kg IV q5min, repeat PRN up to 300mg/hr
  • Beta-blockers (e.g. metoprolol 5mg IV q5m x 3) if blood pressure tolerates

Refractory

• ≥3 episodes within 24 hours considered electrical storm
• May require alternate treatment (i.e. β-blockers, sedation, ablation)

Medication Dosing

Magnesium sulfate 1-2g IV, repeat in 5-15min; then 1-2g/hr infusion IV Magnesium sulfate 25-50mg/kg (max 2g) IV IV Isoproterenol 2-8mcg/min IV infusion IV Amiodarone 150mg IV over 10min, then 1mg/min x6hr, then 0.5mg/min x18hr IV Amiodarone 5mg/kg (max 300mg) IV, may repeat x2 IV Lidocaine 1-1.5mg/kg IV, then 1-4mg/min infusion IV Lidocaine 1mg/kg (max 100mg) IV IV Procainamide 20-50mg/min IV (max 17mg/kg) IV Procainamide 15mg/kg IV over 30-60min IV

Disposition

• Admit with cardiology consult, even if back in normal sinus rhythm
  • Stable patients may be admitted to ward
    • Pads should remain on patient's chest anticipating need for repeat cardioversion
    • All patients should remain on telemetry or full cardio-respiratory monitoring for recurrent events
  • Patients with features of instability or refractory VT are best admitted to CCU or ICU and may require urgent or emergent pacemaker placement

See Also

• Tachycardia (wide)
• Torsades de pointes
• ACLS (Main), PALS (Main)
• Adult Pulseless Arrest, Pediatric pulseless arrest
• Critical care quick reference
• Nonsustained ventricular tachycardia