ECG recognition: the twisting morphology and QT context
Torsades de pointes (TdP) is a specific form of polymorphic ventricular tachycardia occurring in the context of a prolonged QT interval. The name means 'twisting of the points' — the QRS complexes appear to twist around the isoelectric baseline, alternating between positive and negative polarity over a span of several beats.
ECG features: Wide-complex polymorphic tachycardia, usually at 150–300 bpm. The QRS axis rotates continuously. Episodes are characteristically initiated by a short-long-short coupling sequence: a premature beat (short coupling interval) followed by a long pause, followed by another premature beat that lands in the prolonged QT period and initiates the arrhythmia. The initiating event is often an R-on-T PVC — a premature ventricular contraction falling on the T wave of the preceding beat during the period of maximum repolarization heterogeneity.
Distinguishing TdP from VF: TdP has the characteristic axis-twisting morphology with organized, though polymorphic, QRS complexes. VF is chaotic without any organized QRS structure. TdP often terminates spontaneously; VF is always sustained. Both can degenerate into VF.
Causes and risk factors: drugs, electrolytes, and genetic predisposition
Drug-induced TdP is the most common cause in hospitalized patients. QT-prolonging drugs include: antibiotics (azithromycin, fluoroquinolones, azole antifungals), antipsychotics (haloperidol, quetiapine, ziprasidone), antiarrhythmics (amiodarone, sotalol, dofetilide), antidepressants (TCAs, citalopram), antiemetics (ondansetron, metoclopramide), and methadone. Drug combinations are additive and often synergistic — the risk of TdP from two QT-prolonging drugs is greater than the sum of their individual risks.
Electrolyte abnormalities dramatically increase TdP risk: hypokalemia and hypomagnesemia both prolong the QT interval and increase repolarization heterogeneity. Maintaining potassium above 4.0 mEq/L and magnesium above 2.0 mg/dL is the foundation of TdP prevention in high-risk patients on QT-prolonging medications.
Congenital long QT syndrome (LQTS) involves genetic mutations in cardiac ion channels. LQT1 (KCNQ1 mutation) triggers TdP with exercise or swimming. LQT2 (KCNH2 mutation) triggers TdP with sudden loud noises — auditory stimuli in the night. LQT3 (SCN5A mutation) triggers TdP during rest or sleep. Genotype-specific triggers are important for risk counseling.
Treatment: magnesium, overdrive pacing, and defibrillation
Sustained TdP with pulse: IV magnesium sulfate 2g over 1–2 minutes is first-line regardless of serum magnesium level. Magnesium shortens the QT interval and reduces repolarization heterogeneity through mechanisms independent of serum level. Additional doses of 2g over 10 minutes can be given if the arrhythmia continues. Correct hypokalemia aggressively — target K+ above 4.0 mEq/L.
Pulseless TdP or TdP degenerating to VF: defibrillation immediately — do not wait for drug administration. CPR between shocks per ACLS protocol.
Prevention strategy: identify and eliminate causative drugs; correct electrolytes before initiating QT-prolonging agents; establish baseline QTc; monitor QTc trend (alert clinician if QTc exceeds 500 ms or increases >60 ms from baseline); escalate telemetry monitoring for high-risk combinations. Overdrive pacing at 80–90 bpm can terminate TdP and prevent recurrence by shortening the QT interval relative to cycle length.