Torsades de Pointes
Torsades de Pointes is a specific form of polymorphic ventricular tachycardia associated with prolonged QT interval, characterized by QRS complexes that appear to twist around the baseline.
Also known as: TdP, Twisting of the Points
ECG Characteristics
| Heart Rate | 150–300 bpm during the arrhythmia |
| Rhythm | Irregular with characteristic waxing/waning amplitude |
| P Wave | Not visible during the tachycardia |
| PR Interval | Not applicable during TdP; baseline ECG shows prolonged QT |
| QRS Duration | Wide, constantly changing axis and morphology |
Mechanism
Triggered by early afterdepolarizations in the setting of prolonged repolarization (long QT). The shifting QRS axis creates the characteristic twisting morphology as the depolarization wavefront rotates.
Key Features on ECG
- Polymorphic wide complex tachycardia
- QRS axis progressively rotates — spindle-shaped waxing and waning amplitude
- Prolonged QT interval on baseline ECG (typically QTc > 500 ms)
- Often initiated by a short-long-short sequence (PVC → pause → PVC)
- May self-terminate or degenerate into VFib
Causes
- Drug-induced QT prolongation (antiarrhythmics, antibiotics, antipsychotics)
- Congenital long QT syndrome
- Hypokalemia or hypomagnesemia
- Severe bradycardia
- Hypothermia
Clinical Significance
TdP is a medical emergency that may degenerate into ventricular fibrillation. Treatment differs from standard VT — IV magnesium is first-line, and isoproterenol or overdrive pacing increases heart rate to shorten QT. Standard antiarrhythmics that prolong QT (e.g., amiodarone) are contraindicated.
Frequently Asked Questions
Why is magnesium the first-line treatment for TdP?
IV magnesium sulfate suppresses early afterdepolarizations (the trigger for TdP) and stabilizes the myocardial cell membrane. It is effective even in patients with normal serum magnesium levels. It works within minutes and is the recommended first-line therapy regardless of serum magnesium concentration.
What drugs commonly cause QT prolongation and TdP?
Common offenders include Class IA and III antiarrhythmics (sotalol, amiodarone, procainamide), certain antibiotics (fluoroquinolones, macrolides), antipsychotics (haloperidol, droperidol), and antiemetics (ondansetron at high doses). The risk increases with drug combinations, electrolyte abnormalities, and female sex.
How do you distinguish TdP from polymorphic VT without QT prolongation?
TdP specifically occurs in the setting of QT prolongation — check the baseline QT interval before the arrhythmia onset. Polymorphic VT with a normal QT interval is usually ischemia-related and treated differently (standard ACLS with amiodarone). The distinction is critical because TdP treatment differs significantly.
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