Torsade de Pointes

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Torsades de pointes (TdP) is a specific form of polymorphic ventricular tachycardia occurring in the context of QT prolongation — it has a characteristic morphology in which the QRS complexes “twist” around the isoelectric line. Treatment includes empiric administration of 2g MgSO4 and consideration of overdrive pacing to at least 100 bpm (either chemical with isoproterenol or electrical via transvenous pacing). Overdrive pacing works because tachycardia is protective against early afterdepolarizations. The QT interval is inversely proportional to the heart rate; therefore, at faster heart rates, the QT interval is shorter and there is less opportunity for “early afterdepolarizations” (term used to describe abnormal depolarization during phase 2 or phase 3 of the cardiac action potential).

 

Torsades de Pointes.

Examples

ECG Showing Torsade de Pointes

Hypokalemia

While there is quite a bit of baseline artifact, a prolonged QT interval with broad-based T waves is evident. This patient was severely hypokalemic and intermittently went into polymorphic ventricular tachycardia. Overdrive pacing via a temporary transvenous pacer was initiated to avoid further episodes of polymorphic ventricular tachycardia.
ECG Showing Hypokalemia

Hypokalemia

Frequent ventricular ectopy places this patient at risk for torsade de pointes.

References

  1. Al-Khatib SM, Stevenson WG, Ackerman MJ, et al. 2017 AHA/ACC/HRS Guideline for Management of Patients With Ventricular Arrhythmias and the Prevention of Sudden Cardiac Death. Journal of the American College of Cardiology. 2018;72(14):e91-e220.
  2. Isbister GK. Risk assessment of drug-induced QT prolongation. Australian prescriber. 2015;38(1):20-24.
  3. Rischall ML, Smith SW, Friedman AB. Screening for QT Prolongation in the Emergency Department: Is There a Better “Rule of Thumb?” Western Journal of Emergency Medicine. 2020;226(2).