#arrhythmia #channelopathies #LQTS #cardiac-electrophysiology #drug-induced-arrhythmias

Torsades de Pointes

Definition

Torsades de pointes (TdP) is a polymorphic ventricular tachycardia characterised by a twisting morphology of the QRS complex around the isoelectric baseline on ECG, arising from abnormal prolongation of cardiac repolarization. It is the hallmark arrhythmia of long QT syndrome and can degenerate into ventricular fibrillation, causing sudden cardiac death.

Key Concepts

Pathophysiology

EADs as the trigger: TdP arises from abnormal prolongation of phase 3 repolarization, which allows reactivation of L-type Ca2+ channels and late Na+ channels before full repolarization is complete, generating early afterdepolarizations (EADs). If EAD amplitude exceeds threshold, a triggered action potential fires. (sources/channelopathies-jaha-2025, rating: high)
Focal initiation — long-APD zone: TdP begins with focal beats originating in the area of longest repolarization. Multiple premature focal beats in this zone shorten APD locally more than in surrounding myocardium, reversing the normal repolarization gradient. This reversal provides the functional substrate for unidirectional block and re-entry — transitioning TdP from a focal-triggered to a re-entrant mechanism. (sources/repolarisation-jaccep-2023, rating: high)
Spatial repolarization gradient — the critical substrate: It is not prolonged APD per se but the spatial gradient between long and short repolarization regions that generates the re-entry substrate. Large regions of uniformly long repolarization do not predispose to EADs — rather, membrane instability arises at borders between long- and short-APD regions (R-on-T / R-from-T phenomenon). Heterogeneity of repolarization is the necessary substrate for both initiation and perpetuation. (sources/repolarisation-jaccep-2023)
TdP that does not self-terminate degenerates into VF and causes SCD. (sources/channelopathies-jaha-2025)

Repolarization Reserve

Redundant repolarization mechanisms: Repolarization is governed by multiple overlapping currents (IKr, IKs, INa-L, etc.). When one mechanism is already compromised (e.g., a latent LQTS variant reducing IKr), introduction of an IKr-blocking drug depletes the remaining repolarization reserve, unmasking QT prolongation and TdP risk. This framework explains why many drug-induced TdP episodes occur in patients with underlying genetic susceptibility. (sources/drug-arrhythmia-aha-2020, rating: very high)
Latent LQTS prevalence in drug-induced TdP: Approximately 30% of drug-induced QT prolongation patients carry pathogenic variants in one of the 5 major LQTS genes (AHA 2020), though the 2025 arrhythmia genetics review cites only 10-15% as representing unmasked hidden LQTS. The discrepancy reflects different methodologies and gene panels. Neither figure currently supports routine pre-prescription genetic screening for QT-prolonging drugs. (sources/drug-arrhythmia-aha-2020, sources/arrhythmia-genetics-mgenetik-2025)

Acquired (Drug-Induced) TdP

Prevalence and mechanism: Acquired drug-induced TdP is the most common cause of TdP in clinical practice; >200 drugs with TdP potential remain available. Drugs cause TdP primarily through IKr inhibition, prolonging action potential duration and increasing EAD susceptibility. Some drugs additionally augment late sodium current (INa-L): dofetilide, ibutilide, d-sotalol, thioridazine, erythromycin. (sources/drug-arrhythmia-aha-2020, rating: very high)
Amiodarone exception: Amiodarone, unlike quinidine or sotalol, does not increase transmural dispersion of repolarization despite significant QTc prolongation — this partly explains its relatively low TdP incidence compared with other IKr blockers. (sources/drug-arrhythmia-aha-2020, sources/amiodarone-cvdrug-2020)
Flecainide — QRS-driven QTc prolongation without TdP risk: Flecainide prolongs QTc 3-8% but most of this change is due to QRS complex widening (11-27%), not ventricular repolarization prolongation. The JT interval (reflecting true repolarization) remains largely unchanged. Unlike IKr-blocking agents, flecainide does not meaningfully prolong ventricular APD and carries a low TdP risk. This illustrates that QTc prolongation is not universally a marker of TdP risk — the mechanism of QTc change must be considered. (sources/flecainide-af-europace-2011, rating: medium)
Risk factors for drug-induced TdP: QTc >500 ms or increase >=60 ms from baseline; female sex; age >65; bradycardia; acute MI; hypokalaemia; hypomagnesaemia; hypocalcaemia; HFrEF; two or more concurrent QT-prolonging drugs; prior drug-induced TdP; pharmacokinetic drug interactions; renal or hepatic impairment with renally or hepatically cleared drugs. (sources/drug-arrhythmia-aha-2020)
QTc monitoring: In hospitalised patients on antiarrhythmic drugs with known TdP risk: QTc daily; target QTc <500 ms (without QRS prolongation). Long-term QT-prolonging therapy: 12-lead ECG every 3-6 months. Methadone: ECG at opioid treatment program admission, within 30 days if risk factors present, annually or when dose exceeds 120 mg/day. (sources/drug-arrhythmia-aha-2020)

Management of TdP

Acute management: Discontinue offending drug. Correct electrolytes: hypokalaemia, hypomagnesaemia, hypocalcaemia. (sources/drug-arrhythmia-aha-2020, rating: very high)
IV magnesium 1-2 g: Terminates haemodynamically stable TdP regardless of serum magnesium level — mechanism is Ca2+ channel inhibition suppressing EADs (not electrolyte repletion). First-line pharmacological treatment. (sources/drug-arrhythmia-aha-2020)
Recurrent TdP with bradycardia refractory to magnesium: Overdrive pacing or isoproterenol (shortens QT by increasing heart rate, reducing the pause-dependent EAD trigger). (sources/drug-arrhythmia-aha-2020)
Haemodynamically unstable TdP: Defibrillation — synchronisation may be impossible in polymorphic VT. (sources/drug-arrhythmia-aha-2020)
Refractory TdP: Oral mexiletine 200-450 mg/day (shortens QT via INaL inhibition); pretreatment with high-dose magnesium sulfate 5 g over 1h reduces TdP risk when giving ibutilide. (sources/drug-arrhythmia-aha-2020)
Inherited LQTS-TdP prevention: Non-selective beta-blockers (nadolol preferred) first-line. Mexiletine and LCSD for refractory cases. ICD for high-risk or refractory patients. (sources/channelopathies-jaha-2025)

Inherited TdP (LQTS)

In LQTS, loss-of-function mutations in KCNQ1 (LQT1) or KCNH2 (LQT2) reduce repolarizing K+ currents; gain-of-function mutations in SCN5A (LQT3) increase late Na+ current — both mechanisms prolong the QT interval and predispose to TdP. (sources/channelopathies-jaha-2025, rating: high)
TdP is a diagnostic criterion (+1 point) in the Schwartz Score for LQTS. (sources/channelopathies-jaha-2025)
Trigger specificity by subtype: LQT1 events predominantly during exercise (IKs most critical during sympathetic activation); LQT2 events during sudden auditory stimuli or emotion; LQT3 events predominantly at rest/sleep (INaL most prominent with slow heart rates). (sources/channelopathies-jaha-2025)

Sex Hormones and Pregnancy

Sex-based QT risk: Estrogen inhibits IKr (prolonging QT), while testosterone and progesterone shorten QT, explaining the higher TdP risk in postpubertal females vs. males aged 18-40. (sources/channelopathies-jaha-2025, rating: high)
Progesterone as antiarrhythmic in LQT2: Preclinical LQT2 rabbit models show progesterone eliminates polymorphic VT and prevents SCD; estradiol promotes it. The postpartum fall in progesterone is the primary mechanistic driver of the elevated 9-month postpartum TdP/SCD risk in LQT2 patients. (sources/lqts-pregnancy-medicina-2022, rating: medium)
Pregnancy: Relatively protective against TdP (physiological tachycardia shortens QT). The 9-month postpartum period carries a 2.7-fold increased cardiac event risk and 4.1-fold life-threatening event risk. (sources/lqts-pregnancy-medicina-2022)
See concepts/LQTS-Pregnancy-Management for the full three-tier delivery risk stratification and postpartum management framework.

Cancer Therapy and QT Prolongation

QT prolongation occurs in up to 22% of cancer patients across drug classes. Arsenic trioxide (acute promyelocytic leukaemia) causes QT prolongation in 26-93% — the highest incidence of any cancer drug. Despite this, life-threatening arrhythmias (TdP, VF) occur in <1% of patients receiving QT-prolonging cancer therapies. (sources/arrhythmia-cardio-oncology-aha-2021, rating: very high)
Mechanisms: Direct K+ channel blockade (same as non-cancer drugs); PI3K pathway inhibition (many TKIs) causes ventricular repolarization delay independent of direct channel block. (sources/arrhythmia-cardio-oncology-aha-2021)
Fridericia formula (QTcF = QT/RR^(1/3)) preferred over Bazett (QTcB) in cancer patients — more accurate at heart rate extremes (tachycardia from deconditioning/pain, bradycardia from cancer drugs). (sources/arrhythmia-cardio-oncology-aha-2021)
Ribociclib + tamoxifen carries the highest QT risk in breast cancer: >5% developed QTc >480 ms in MONALEESA-7 — this combination is specifically contraindicated. Ribociclib + AI or fulvestrant causes QTc >480 ms in 3.3-5.6%. Palbociclib causes hypertension rather than QT prolongation; abemaciclib has no significant CV effects. (sources/Hormonal-Rx-AHA-2021, rating: high)
Mexiletine: Emerging evidence for arsenic trioxide-induced QT prolongation and recurrent TdP; also effective for acquired long QT refractory to conventional measures (JACC 2015; n=12). RCTs needed. (sources/arrhythmia-cardio-oncology-aha-2021, sources/drug-arrhythmia-aha-2020)
No standardised QT monitoring protocol exists for cancer therapy — each drug label carries different instructions. (sources/arrhythmia-cardio-oncology-aha-2021)
See concepts/Cancer-Associated-Arrhythmia for the full cancer QT management framework.

Contradictions / Open Questions

TdP as LQTS-specific vs. acquired QT prolongation: TdP is the hallmark arrhythmia of inherited LQTS, but acquired QT prolongation from drugs or electrolyte disturbances causes TdP in structurally normal hearts by the same EAD/re-entry mechanism. The same ECG morphology in different clinical contexts demands different management (acquired: remove trigger + magnesium + pacing; inherited: beta-blockers +/- ICD), and the two entities are easily confused when clinical history is incomplete. (sources/channelopathies-jaha-2025, sources/VA-SCD-ESC-2022)
Latent LQTS prevalence in drug-induced TdP — discrepant estimates: AHA 2020 reports ~30% of drug-induced TdP patients carry pathogenic LQTS gene variants; the 2025 arrhythmia genetics review cites only 10-15%. Likely reflects different gene panels and patient populations. Neither figure currently supports routine pre-prescription genetic screening for QT-prolonging drugs. (sources/drug-arrhythmia-aha-2020, sources/arrhythmia-genetics-mgenetik-2025)
Sex-based risk — clinical actionability limited: Estrogen's inhibition of IKr and postpartum progesterone fall provide strong biological explanations for female TdP excess. However, no guideline currently recommends sex-stratified QTc monitoring intervals, different beta-blocker dosing, or ICD thresholds based on hormonal status — and despite compelling preclinical evidence, no guideline recommends postpartum progesterone supplementation in LQT2. Biological mechanism has not translated into sex-stratified clinical recommendations. (sources/channelopathies-jaha-2025, sources/lqts-pregnancy-medicina-2022)
QTc prolongation is not a uniform TdP surrogate: Flecainide prolongs QTc via QRS widening with minimal repolarization change and low TdP risk; amiodarone prolongs QTc substantially but has low TdP incidence due to absence of transmural dispersion increase. Conversely, drugs with modest QTc prolongation (dofetilide, sotalol) carry significant TdP risk. QTc alone is an imperfect TdP surrogate — the mechanism of QTc change and transmural repolarization heterogeneity are the biologically relevant variables. (sources/drug-arrhythmia-aha-2020, sources/flecainide-af-europace-2011)

Connections

Related to concepts/Cardiac-Action-Potential
Related to concepts/Sudden-Cardiac-Death
Related to concepts/Schwartz-Score
Related to concepts/Left-Cardiac-Sympathetic-Denervation
Related to concepts/Drug-Induced-Arrhythmia
Related to concepts/Cardiac-Repolarization
Related to concepts/LQTS-Pregnancy-Management
Related to concepts/Cancer-Associated-Arrhythmia
Related to concepts/Hormonal-Therapy-CV-Risk
Related to entities/Long-QT-Syndrome
Related to entities/KCNQ1
Related to entities/KCNH2
Related to entities/SCN5A
Related to entities/Amiodarone
Related to entities/Flecainide
Related to sources/repolarisation-jaccep-2023
Related to sources/Hormonal-Rx-AHA-2021
Related to sources/flecainide-af-europace-2011