Cardiology · Arrhythmias
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Torsades de Pointes is a polymorphic ventricular tachycardia characterized by a twisting of the QRS complexes around the isoelectric line.
The hallmark ECG finding is a prolonged QT interval (typically >500 ms) preceding the onset of the arrhythmia.
Sustained polymorphic VT, including torsades, is treated as unstable regardless of blood pressure; first-line therapy is immediate unsynchronized defibrillation (2025 AHA ALS).
For recurrent, self-terminating torsades with a long QT, intravenous magnesium sulfate is the preferred drug to suppress recurrences, even when serum magnesium is normal.
Acquired Torsades is most commonly caused by electrolyte disturbances (hypokalemia, hypomagnesemia) or QT-prolonging medications.
Common offending drug classes include antiarrhythmics (Class IA and III), macrolides, fluoroquinolones, and antipsychotics.
Congenital Long QT syndrome is often associated with autosomal dominant (Romano-Ward) or autosomal recessive (Jervell and Lange-Nielsen) inheritance patterns.
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A 62-year-old woman is brought to the emergency department after a syncopal episode. She has a history of depression and was recently started on levofloxacin for a urinary tract infection. On arrival she is alert, with a pulse of 88/min and a blood pressure of 124/76 mmHg. Telemetry shows sinus rhythm with a QTc of 560 ms, interrupted by recurrent, self-terminating runs of polymorphic ventricular tachycardia lasting a few seconds with a twisting appearance of the QRS complexes. Levofloxacin is discontinued and defibrillator pads are placed.
Which medication is most appropriate to suppress further episodes of this arrhythmia?
Intravenous magnesium sulfate
This patient has recurrent, self-terminating torsades de pointes from acquired QT prolongation (levofloxacin). Intravenous magnesium sulfate (2 g) is the preferred drug to suppress recurrences, even when serum magnesium is normal; the 2025 AHA ALS guideline states magnesium may be considered for recurrent polymorphic VT associated with a long QT interval (Class 2b). If an episode becomes sustained, polymorphic VT is treated as unstable and managed with immediate unsynchronized defibrillation (Class 1). QT-prolonging antiarrhythmics such as amiodarone, procainamide, and sotalol are generally avoided; isoproterenol or overdrive pacing is reserved for pause-dependent episodes that recur despite magnesium.
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Etiology / Epidemiology
Occurs in patients with prolonged QT interval due to electrolyte disturbances or QT-prolonging medications.
Clinical Manifestations
Polymorphic ventricular tachycardia with twisting of the points; presents as syncope or sudden cardiac death.
Diagnosis
ECG shows polymorphic QRS complexes with a QTc > 500 ms.
Treatment
Sustained episodes: immediate unsynchronized defibrillation; IV magnesium sulfate to suppress recurrences; avoid antiarrhythmics that prolong QT.
Prognosis
High risk of progression to ventricular fibrillation; warrants immediate correction of underlying triggers.
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Epidemiology & Etiology
Commonly triggered by hypokalemia, hypomagnesemia, or hypocalcemia. Iatrogenic causes include macrolides, fluoroquinolones, and antipsychotics. Patients with congenital long QT syndrome are at highest risk.
Pertinent Anatomy
Involves the ventricular myocardium and the His-Purkinje system. Repolarization abnormalities lead to early afterdepolarizations that trigger re-entrant circuits.
Pathophysiology
Delayed repolarization allows for early afterdepolarizations (EADs) during phase 3 of the action potential. These EADs trigger a polymorphic ventricular tachycardia that appears to twist around the isoelectric line. If persistent, the rhythm degenerates into ventricular fibrillation.
Clinical Manifestations
Patients typically present with syncope, palpitations, or seizure-like activity due to cerebral hypoperfusion. The twisting of the points appearance on ECG is highly characteristic. Sudden cardiac arrest is a frequent initial presentation in undiagnosed cases.
Diagnosis
ECG is the key diagnostic test. Look for a QTc > 500 ms and polymorphic QRS complexes that change amplitude and polarity. Calculate the QTc (Bazett's formula is most common but overcorrects at fast and undercorrects at slow heart rates; AHA/ACCF/HRS 2009 recommend a linear regression correction over Bazett, and Fridericia's formula is a common alternative).
Treatment
Sustained polymorphic VT, including torsades, is treated as hemodynamically and electrically unstable: deliver immediate unsynchronized defibrillation (2025 AHA ALS, Class 1). To suppress recurrences in the setting of a long QT, give IV magnesium sulfate (2 g bolus) even if serum magnesium is normal (2025 AHA ALS, Class 2b), stop QT-prolonging drugs, and replete potassium to the high-normal range. For pause- or bradycardia-dependent recurrences of acquired torsades despite magnesium, isoproterenol or temporary overdrive pacing can be used. Avoid Class IA, IC, and III antiarrhythmics, which can further prolong the QT interval or are proarrhythmic.
Prognosis
High risk of ventricular fibrillation and death if untreated. Warrants continuous cardiac monitoring and aggressive electrolyte repletion to prevent recurrence.
Differential Diagnosis
Ventricular Tachycardia: Monomorphic QRS complexes
Ventricular Fibrillation: Chaotic, irregular rhythm without distinct QRS
Brugada Syndrome: ST elevation in V1-V3 with RBBB pattern
Hyperkalemia: Peaked T waves and widened QRS
Wolff-Parkinson-White: Delta wave and short PR interval