What are the signs of torsades de pointes?

Signs of Torsades de Pointes (TdP)

The most important signs of torsades de pointes include a characteristic polymorphic ventricular tachycardia with twisting QRS complexes around the isoelectric line, occurring in the setting of a prolonged QT interval (typically >500 ms), and often initiated by a short-long-short R-R cycle sequence. 1

ECG Characteristics

Diagnostic Features

• QT Interval Abnormalities:

  • Marked QTc prolongation >500 ms (high-risk threshold) 1
  • Distorted T-U waves, often with T-wave flattening or bifid T waves 1
  • Exaggerated QT prolongation after a pause 1

• Arrhythmia Pattern:

  • Polymorphic ventricular tachycardia with twisting QRS morphology 1, 2
  • Heart rate typically between 160-240 beats per minute 2
  • "Warm-up" phenomenon (initial R-R cycles longer than subsequent cycles) 1
  • Abrupt switching of QRS morphology from predominantly positive to predominantly negative complexes 1

Triggering Sequence

• Short-long-short R-R interval sequence before TdP onset 1
• Typically initiated by a PVC that falls near the peak of the distorted T-U complex 1
• Often occurs after a pause (e.g., after an ectopic beat or during transient AV block) 1

Premonitory Signs

• Macroscopic T-wave alternans (a rare but ominous sign) 1
• Ventricular ectopy and couplets 1
• Increasing QT-U prolongation and distortion, especially after pauses 1
• Tpeak-Tend interval prolongation (terminal portion of T wave) 1

Clinical Presentation

• Self-terminating episodes causing dizziness and syncope 3
• May occasionally progress to ventricular fibrillation and sudden death 1, 3
• Often occurs in the setting of QT-prolonging medications 1
• Frequently terminates spontaneously, with the last 2-3 beats showing slowing 1

Risk Factors for TdP

• QT Interval:

  • Each 10 ms increase in QTc contributes approximately 5-7% increased risk 1
  • QTc >500 ms associated with 2-3 fold higher risk 1

• Medication-Related:

  • Use of QT-prolonging drugs (especially Class IA and III antiarrhythmics) 1
  • Concurrent use of multiple QT-prolonging medications 1
  • Rapid intravenous infusion of QT-prolonging drugs 1

• Electrolyte Abnormalities:

  • Hypokalemia 1, 4
  • Hypomagnesemia 4
  • Hypocalcemia 2

• Patient Factors:

  • Female sex 2
  • Bradycardia or heart block 1, 5
  • Underlying heart disease 6
  • Subclinical congenital LQTS 1

Management Considerations

• Immediate direct-current cardioversion for sustained TdP 1
• Intravenous magnesium sulfate (2g) as first-line therapy regardless of serum magnesium level 1
• Temporary transvenous pacing at rates >70 beats per minute 1
• Isoproterenol infusion to increase heart rate 1, 7
• Potassium repletion to levels of 4.5-5 mmol/L 1
• Discontinuation of culprit QT-prolonging drugs 1

Common Pitfalls

• Failing to recognize the characteristic short-long-short initiating sequence 1
• Misinterpreting TdP as other forms of ventricular tachycardia 7
• Using standard antiarrhythmic drugs (especially QT-prolonging agents) which may worsen TdP 7
• Overlooking premonitory signs such as T-wave alternans or increasing QT prolongation 1
• Not identifying and correcting underlying electrolyte abnormalities 1, 4
• Failing to recognize drug-induced TdP as a potential sentinel event for congenital LQTS 1

Early recognition of these signs is critical as TdP can be effectively managed with prompt intervention, but may progress to ventricular fibrillation and sudden cardiac death if left untreated.