Torsades de Pointes (TdP)

Definition and ECG Features

Torsades de pointes ("twisting of the points" in French) is a paroxysmal form of polymorphic ventricular tachycardia that occurs in the setting of a prolonged QT interval. It has three defining ECG criteria:

Ventricular rate >200 beats/min
Undulating QRS axis - the polarity of complexes appears to shift or "twist" around the isoelectric baseline
Paroxysms lasting <90 seconds (self-terminating in most cases)

TdP fits within the tachycardia classification as a wide-complex, polymorphic tachycardia:

Tachycardia classification flowchart showing TdP under wide-complex polymorphic VT

Pathophysiology

The underlying mechanism involves abnormal ventricular repolarization. Prolonged action potential duration leads to a reduced repolarization reserve, which predisposes cardiac cells - especially Purkinje fibers - to early afterdepolarizations (EADs). These EADs serve as the triggered activity that initiates and maintains the arrhythmia.

Key electrophysiological point: action potential prolongation is least marked at fast rates (where it is desirable) and most marked at slow rates - hence why TdP is characteristically pause-dependent in its acquired form. A long-short RR sequence (a sinus beat followed by a long pause, then a short coupling interval) is the typical trigger.

Hypokalemia worsens this through a separate mechanism: hypokalemia downregulates Na+/K+-ATPase, leading to intracellular Na+ and Ca2+ overload, which increases calmodulin kinase II activity and activates late Na+ and Ca2+ currents - further reducing repolarization reserve. - Brenner and Rector's The Kidney

Classification

Congenital (Inherited) Long QT Syndrome

Mutations affecting ion channel proteins (most commonly KCNQ1, KCNH2, SCN5A)
Prevalence estimated at ~1/988-1/2500
Can be triggered by exercise, startle, or emotional stress depending on genotype
~25% of patients continue experiencing arrhythmias on full-dose beta-blocker therapy

Acquired Long QT / TdP

More common than the congenital form. The acquired form is pause-dependent and triggered by slow heart rate. Causes include:

Electrolyte disturbances:

Hypokalemia (most common)
Hypomagnesemia

Drugs (the leading cause - see below)

Other causes:

Hypothermia
CNS injury (especially subarachnoid hemorrhage)
Bradyarrhythmias
Liquid protein diets / anorexia nervosa
Drug interactions (one agent alone may be safe, combination causes QT prolongation)

QT-Prolonging Drugs

A broad list of agents can cause acquired TdP. Risk categories include:

Drug Class	Examples
Class IA antiarrhythmics	Quinidine, procainamide, disopyramide
Class III antiarrhythmics	Sotalol, dofetilide, amiodarone, ibutilide
Antipsychotics	Haloperidol, ziprasidone, quetiapine, clozapine
Antibiotics	Erythromycin, moxifloxacin, azithromycin
Antiemetics	Ondansetron, domperidone
Opioids	Methadone
Antifungals	Fluconazole
Antihistamines	Terfenadine (withdrawn), astemizole (withdrawn)

Class IA and IC antidysrhythmics are contraindicated in patients with TdP - Rosen's Emergency Medicine
An important practical note from Katzung: "Although most drugs in the class cause QT prolongation, there is considerable variability among drugs in their proarrhythmic tendency to cause torsades de pointes despite significant QT-interval prolongation." QT prolongation alone may not fully predict TdP risk.

Risk Factors

Female sex - Women are at consistently higher risk (sex hormones modify cardiac ion channels; testosterone deficiency in men treated for prostate cancer also increases risk)
Greater degree of QT prolongation or QT alternans
Hypokalemia / hypomagnesemia
Bradycardia
Underlying structural heart disease
Polypharmacy with QT-prolonging agents
History of syncope or prior TdP

Clinical Presentation

TdP typically presents in short self-terminating bursts causing palpitations and syncope. If sustained, it can degenerate into ventricular fibrillation and cardiac arrest. It may be misdiagnosed as seizures - particularly relevant in patients on psychiatric medications where TdP/syncope may masquerade as non-epileptic events. - Kaplan & Sadock's Comprehensive Textbook of Psychiatry

Treatment

Acute Management (Acquired TdP)

Intervention	Details
IV Magnesium sulfate	1-2 g IV rapidly (first-line even without documented hypomagnesemia); may give up to 4 g total; prevents recurrence
Correct electrolytes	Replete K+ (target ≥4.5 mEq/L) and Mg2+
Increase heart rate	Target 100-120 bpm to shorten repolarization
Overdrive pacing	External/transvenous pacing at rate > intrinsic rate
Isoproterenol infusion	Chemical overdrive; beta-adrenergic stimulation increases rate
Discontinue offending drugs	Remove all QT-prolonging agents
Electrical cardioversion	For unstable patients or sustained TdP (synchronization may not be possible)

The rationale for increasing heart rate: at faster rates, action potential prolongation is less pronounced, which reduces the substrate for EADs.

Do NOT use Class IA or IC antiarrhythmics - they worsen QT prolongation and increase TdP risk.

Chronic Management (Congenital LQTS)

Beta-blockers are first-line (metoprolol 50-100 mg/day, atenolol 50 mg/day, or nadolol 40 mg/day) - success influenced by sex, genotype, and degree of QT prolongation
ICD - recommended for aborted cardiac arrest; also for patients who fail beta-blocker therapy (~25% of patients)
Left cardiac sympathetic denervation - substantially reduces TdP and syncope in high-risk patients and decreases ICD shock frequency
Avoid all QT-prolonging drugs and relevant triggers (exercise, startle - depending on genotype)

- Goldman-Cecil Medicine; Braunwald's Heart Disease

Key Points Summary

TdP is polymorphic VT + prolonged QT interval; "twisting" QRS morphology at >200 bpm in bursts <90 seconds
Acquired form (far more common) is pause-dependent; congenital form may be triggered by adrenergic stress
Women are more susceptible due to hormonal modulation of ion channels
IV magnesium sulfate is the mainstay of acute treatment regardless of Mg2+ levels
Increasing heart rate (pacing or isoproterenol) breaks the cycle by shortening repolarization
Avoid Class IA/IC agents; remove all offending drugs

Recent evidence note: A 2025 systematic review and meta-analysis (PMID 41137322) specifically addressed QTc prolongation and TdP risk in methadone maintenance treatment, confirming this as an important clinical concern. A 2025 systematic review (PMID 41255343) examined QT prolongation in acute antipsychotic poisoning. These reinforce established textbook guidance without contradicting current management principles.

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