Torsades de pointes

Background

Form of polymorphic VTach
- Gradual change in the amplitude of QRS complexes and twisting around isoelectric line
Associated with congenital or acquired prolonged QT

Common Causes

POINTES mnemonic:

Phenothiazines
Other medications (ie TCAs)
Intracranial bleed
No known cause (idiopathic)
Type I antiarrhythmics (quinidine, procainamide, disopyramide)
Electrolyte abnormalities (hypoK & hypoMg)
Syndrome of Prolonged QT (aka Long QT Syndrome)
Other causes:

Clinical Features

Syncope
Dizziness, lightheadedness
Palpitations
Sudden cardiac arrest

Differential Diagnosis

Drug induced
Congenital long QT
Hypocalcemia
Hypomagnesemia
Hypokalemia
Hypothermia
POINTES as above

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

Workup

ECG
BMP, Mg, Phos

Diagnosis

Classic torsades in 12-lead

Torsades de Pointes (TdP) in patient with a potassium of 2.4 mmol/L and a magnesium of 1.6mg/dL.

ECG showing the QRS complexes “twisting” around the isoelectric line

Management

Increasing HR decreases QT interval

Magnesium sulfate - decreases calcium influx
- 1-2gm IV over 1-2 min, repeat in 5-15min; then 1-2gm/hr (3-10mg/min) drip
  - Danger of hypermagnesemia → depressed neuromuscular function and respiratory drive, so monitor closely
  - Supplement with K+
Isoproterenol - Increases HR / AV conduction
- 2-8 mcg/min
- Target HR > 90 bpm
Overdrive Pacing - Atrial > Ventricular pacing
- Goal HR 90-120
- Note: Not a treatment for TdP, but useful in maintaining sinus rhythm
Defibrillation / synchronized cardioversion - Patient in extremis
AVOID amiodarone and procainamide, which may worsen prolonged QT
Lidocaine (a class Ib antiarrhythmic drug) shortens the QT interval and may be effective especially for drug-induced torsades de pointes.

Disposition

Admit

References

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