Long QT and Channelopathies

Meet the patient

A 14-year-old girl is pulled unconscious from the school swimming pool. She is back to normal within a minute, with no tongue-biting, no incontinence, and no post-ictal confusion. Her uncle died suddenly at 24. The ambulance crew have labelled it "a seizure, probably", but her resting QTc is 520 ms.^[1][2]

The two questions that decide her next decade are the two that decide every channelopathy: is the heart structurally normal? (it is — which is exactly why the diagnosis is missed and filed as "epilepsy") and what was she doing when it happened? (the circumstance is the genotype: swimming screams LQT1, the alarm clock screams LQT2, sleep screams LQT3). The echo is normal, the ECG is everything, and the family tree is lethal if you do not climb it.^[1][8]

What a channelopathy is — a structurally normal heart that is electrically unstable

The cardiac channelopathies are a group of inherited disorders caused by mutations in the genes encoding cardiac ion channels or their accessory regulatory proteins. They share a paradoxical and clinically dangerous phenotype: a heart that is structurally normal on echocardiography yet electrically unstable, predisposing to syncope, torsades de pointes (TdP), ventricular fibrillation (VF), and sudden cardiac death (SCD) — most often in children, adolescents, and young adults. The five clinically important syndromes are congenital long QT syndrome (LQTS), Brugada syndrome, catecholaminergic polymorphic ventricular tachycardia (CPVT), short QT syndrome (SQTS), and early repolarisation syndrome (ERS).^[1]

LQTS has a prevalence of approximately 1 in 2,000 to 2,500 and is the most common of the group. The others are rarer — a type 1 Brugada ECG is found in 0.15 to 0.27 percent of adults in Japan and 0.18 percent in the Philippines (the prevalence is strikingly higher in East and Southeast Asia than in Europe), CPVT is approximately 1 in 10,000, and SQTS is exceptionally rare. Because the channelopathies leave no scar at autopsy, they are the prototypical cause of autopsy-negative sudden cardiac death in the young, which is why post-mortem genetic testing (the "molecular autopsy") and cascade screening of first-degree relatives are now standard practice after any unexplained death in a young person.^{[4][12][27][28]}

The clinically important distinction that frames this entire topic is congenital versus acquired long QT. Congenital LQTS is genetic and life-long; acquired LQTS from QT-prolonging drugs, electrolyte disturbance, bradycardia, or hypothyroidism is far more common in routine practice and is the single most preventable cause of drug-induced TdP. Every prescriber must therefore understand both the inherited forms and the drug-electrolyte interactions that produce the same ECG signature. ^[1]

Classification

The 2013 HRS/EHRA/APHRS expert consensus divides the inherited primary arrhythmia syndromes by gene and dominant phenotype.^[1] The three common LQTS genotypes account for over 90 percent of genotype-positive cases and have gene-specific triggers that examiners always probe.

^{[8] [13] [16] [17] [28]}

Enlarge

The rare LQTS genotypes are recognised but rarely the discriminator at MBBS level. LQT4 (ANK2, ankyrin-B), LQT5 (KCNE1), LQT6 (KCNE2), LQT7 (Andersen-Tawil syndrome, KCNJ2, with periodic paralysis and dysmorphism), LQT8 (Timothy syndrome, CACNA1C gain-of-function, with syndactyly and autism), and LQT9 to 15 are individually uncommon. Jervell and Lange-Nielsen syndrome is the recessive form caused by homozygous or compound heterozygous KCNQ1 or KCNE1 mutations, characterised by congenital profound sensorineural deafness and a particularly severe cardiac phenotype with early-onset SCD.^[1]

^{[7] [11] [12] [29]}

Epidemiology & Risk Factors

^{[12] [27] [28]}

The dominant epidemiological clue across all five syndromes is a family history of sudden cardiac death in a relative under 40, particularly unexplained drowning (a classic LQT1 presentation during swimming), a single-vehicle night-time car crash (often a syncopal event at the wheel), or sudden infant death syndrome. Autosomal dominant inheritance (Romano-Ward) is the typical pattern in LQTS, CPVT, and most Brugada and SQTS kindreds, conferring a 50 percent risk to first-degree relatives; Jervell-Lange-Nielsen is the recessive exception.^[1]

Several acquired factors amplify the risk of an event in a genetically predisposed individual. Female sex lengthens the baseline QTc and confers higher risk, particularly in LQT2 post-puberty and through the postpartum period. Hypokalaemia, hypomagnesaemia, and hypocalcaemia all prolong repolarisation. Bradycardia (sleep, AV block, drugs) is arrhythmogenic in LQT3. QT-prolonging drugs are the single most important iatrogenic precipitant of TdP and are responsible for most acquired LQTS in clinical practice.^[1][4]

Pathophysiology

The unifying mechanism across the LQTS genotypes is prolongation of the ventricular action potential, which manifests on the surface ECG as a lengthened QT interval. The mechanism differs by genotype. In LQT1, a loss-of-function mutation in KCNQ1 reduces the slowly activating delayed rectifier potassium current (IKs), shortening repolarising outward current. In LQT2, a loss-of-function mutation in KCNH2 (hERG) reduces the rapidly activating delayed rectifier potassium current (IKr) — and because hERG is the channel most commonly blocked by pharmaceuticals, this same current is responsible for the vast majority of drug-induced LQTS. In LQT3, a gain-of-function mutation in SCN5A enhances the late sustained sodium current (late INa), which keeps depolarising current flowing long after the upstroke and preferentially prolongs the action potential at slow heart rates — explaining why LQT3 events cluster during sleep and rest.^[1]

Whatever the ionic mechanism, prolonged repolarisation produces two downstream consequences that drive arrhythmogenesis. The first is increased dispersion of repolarisation — different layers of myocardium (notably mid-myocardial M cells) repolarise at markedly different times, creating a substrate for re-entry. The second is the appearance of early afterdepolarisations (EADs), oscillations of the membrane potential during the prolonged plateau phase that can trigger a premature ventricular beat, which then degenerates into polymorphic VT (TdP). The hallmark ECG of TdP is polymorphic VT with twisting of the QRS axis around the baseline, typically initiated by a short-long-short R-R sequence and often self-terminating but recurrent, with the potential to degenerate into VF. ^[1]

Enlarge

CPVT has a fundamentally different mechanism. A mutation in the cardiac ryanodine receptor (RYR2) or in calsequestrin (CASQ2) causes spontaneous diastolic calcium leak from the sarcoplasmic reticulum under adrenergic stimulation. The resultant intracellular calcium overload generates delayed afterdepolarisations (DADs) — different from the EADs of LQTS — that fire premature beats in bigeminal patterns and the characteristic bidirectional VT (alternating QRS axis beat-to-beat, superficially resembling supraventricular tachycardia with aberrancy). Because the resting membrane is normal, the resting ECG is normal, and the diagnosis is made by provoking the arrhythmia with exercise or adrenaline.^[6]

Brugada syndrome results from a loss-of-function mutation in SCN5A (or, less commonly, in CACNA1C, GPD1-L, or other sodium-calcium channel subunits). The reduced inward sodium current disproportionately abbreviates the action potential in the right ventricular epicardium, abolishing the action potential dome and creating a transmural voltage gradient that produces the characteristic coved ST elevation in V1 to V3. The same substrate supports phase-2 re-entry and polymorphic VT/VF, which typically occurs at rest or during sleep, when vagal tone is high and sodium channel availability is reduced, and is often precipitated by fever (which further worsens sodium-channel trafficking).^[7]

Short QT syndrome is caused by gain-of-function mutations in the same channels that are lost in LQTS (KCNH2, KCNQ1, KCNJ2), producing abbreviated action potentials, a very short QTc, and marked shortening of atrial and ventricular refractoriness that predisposes to both atrial fibrillation and VF.^[10] Early repolarisation syndrome is mechanistically related: an accentuated outward potassium current (mediated by IKATP, IKr, or IKs) generates a J-point notch or slur that, in the inferior or lateral leads, creates a substrate for phase-2 re-entry and idiopathic VF.^[11][12]

Clinical Presentation

The dominant clinical manifestations across all the channelopathies are syncope, seizure-like events, cardiac arrest, and sudden cardiac death in a young, otherwise healthy individual. The single most diagnostically powerful clue is the circumstance of the event, which is why the history alone often points to the genotype.^[1]

In LQT1, syncope is classically triggered by exercise — especially swimming — and by emotional stress; the swimming phenotype is so characteristic that any unexplained drowning in a competent swimmer should prompt LQTS evaluation of the family. In LQT2, the trigger is auditory — a sudden loud noise such as an alarm clock, a doorbell, a ringing telephone, or an infant's cry — and emotional stress, with a marked increase in risk during the 9 months postpartum (hazard ratio 2.7 versus the period before first conception, and highest in LQT2). In LQT3, events occur at rest or during sleep, and the patient may give a history of nocturnal syncope or a parent may describe a child found pulseless in the cot.^[1][8][22]

The syncope of LQTS is often misdiagnosed as epilepsy for years before the correct diagnosis is made, because the cerebral hypoperfusion of TdP can produce brief tonic-clonic movements indistinguishable from a generalised seizure. The discriminating features are: syncope during exercise or with a recognisable trigger (rather than the typical aura and post-ictal confusion of true epilepsy), a family history of SCD, no post-ictal state, and a prolonged or atypical QTc on ECG.^[1]

In CPVT, syncope or cardiac arrest is provoked by exercise or strong emotion in a child whose resting ECG is entirely normal; the bidirectional VT is reproducibly induced by exercise testing. In Brugada, syncope or VF typically occurs at rest, during sleep, after a large meal, or during a febrile illness; agonal nocturnal respiration is a recognised presentation. In SQTS, the patient may present with atrial fibrillation at a young age, syncope, or sudden death. In ERS, the presentation is idiopathic VF — typically in a young male with a J-point pattern in the inferior or lateral leads — and a family history of early SCD.^[7][10][11]

Examination between events is almost always normal, which is itself a clue. Clues to syndromic forms include syndactyly (Timothy syndrome, LQT8), dysmorphic facies with periodic paralysis (Andersen-Tawil, LQT7), and congenital sensorineural deafness (Jervell-Lange-Nielsen). ^[1]

Differential Diagnosis

The differential of QT prolongation and an unexplained syncopal event in a young person is wide, and several diagnoses are dangerous to miss. The most important differentials for clinical practice are:^[1][3]

The cardinal rule is that any patient with QT prolongation must have acquired causes actively excluded before the diagnosis of congenital LQTS is made: review every drug against the CredibleMeds list, check potassium, magnesium, calcium, and thyroid function, and consider structural disease with echocardiography. Drug-induced QT prolongation is overwhelmingly an hERG-channel blockade phenomenon — the IKr current carried by the KCNH2/hERG channel is exquisitely sensitive to a structurally diverse range of pharmaceuticals because the channel's inner cavity is large and aromatic, accommodating many drug classes. CredibleMeds grades that risk in three categories, and the definitions — not a memorised drug-to-tier list — are what a prescriber needs: Known Risk of TdP (drugs that "should only rarely, if ever, be given to patients with congenital LQTS because the danger is clear"), Possible Risk of TdP (drugs "found to increase QT intervals in some patients", usable under specialist supervision if medically necessary), and Conditional Risk of TdP (drugs whose "risk is confined to certain conditions, e.g. overdose, excessive duration of treatment, use with diuretics or drugs that block their elimination, or patients with other risk factors"). A fourth, broader Drugs to Avoid in congenital LQTS list adds agents with adrenaline-like effects that do not themselves prolong the QT. Category membership is revised continuously, so the list — not a textbook table — must be checked at the point of prescribing. Note that the obvious antiemetic substitutions are not safe ones: ondansetron and domperidone both prolong repolarisation and both provoked early afterdepolarisations and torsades-like polymorphic VT in a sensitive proarrhythmia model.^[1][25]

A separate category of acquired LQTS that examiners test is the pause-dependent form, in which TdP is initiated by a short-long-short R-R sequence — a premature ventricular beat, a compensatory pause, then another premature beat that falls on the prolonged QT of the post-pause beat and degenerates into TdP. Pause-dependent TdP is the typical mechanism in bradycardia, high-grade AV block, and after a long asystolic pause, and is the form most responsive to isoprenaline or overdrive pacing — but isoprenaline belongs to the acquired setting, because it is contraindicated in congenital long QT, where it can paradoxically lengthen the QT interval. In contrast, pause-independent TdP (typical of congenital LQTS with adrenergic surges) is more responsive to beta-blockade. Recognising the short-long-short initiating sequence on a telemetry strip is a high-yield exam pearl and predicts the response to pacing versus beta-blockade. ^[1][24]

Clinical & Bedside Assessment

The focused history in a suspected channelopathy must capture four elements. First, the circumstance of the event — exercise versus auditory trigger versus rest versus sleep, the timing relative to emotional stress or the postpartum period, and any prodrome (true LQTS events often have little or no prodrome). Second, the family history — explicitly ask about sudden death in relatives under 40, unexplained drowning, cot death, sudden infant death syndrome, and single-vehicle accidents, and construct a three-generation pedigree. Third, the medication history, including over-the-counter and recreational drugs (cocaine, methadone). Fourth, the past medical history — deafness (JLN), periodic paralysis (Andersen-Tawil), syndactyly or autism (Timothy), seizures mislabelled as epilepsy.^[1]

Bedside examination is usually normal. Look specifically for syndromic features: measure blood pressure ( exclude HCM with murmur, aortic stenosis), palpate the precordium (structurally normal in all channelopathies), and inspect for dysmorphism, syndactyly, scoliosis, and low-set ears. Perform a complete neurological examination if the presentation was a seizure-like event. ^[1]

The ECG is the single most important bedside test and is covered in detail in the next section. Manual QTc measurement is mandatory — automated readings are unreliable, particularly in the presence of T-wave morphology changes. ^[1]

Investigations

The cornerstone of investigation is the 12-lead ECG with manual QTc measurement. Use Bazett's formula (QTc = QT divided by the square root of the RR interval in seconds), which is reasonably accurate between 60 and 100 beats/min but overcorrects at faster rates and undercorrects at slower ones; Fridericia's (QTc = QT divided by the cube root of RR) is preferred at extremes of heart rate. Measure in lead II or V5 to V6 across 3 to 5 beats and use the teach-the-tangent method to identify the T-wave end. By the 2013 HRS/EHRA/APHRS criteria, LQTS is diagnosed by a Schwartz risk score of 3.5 or more, or a QTc of 500 ms or more on repeated ECGs, in each case with secondary causes excluded, or by a pathogenic variant in an LQTS gene whatever the QTc. A QTc above 500 ms carries a two- to three-fold increased risk of torsades in any patient.^{[1][2][24][28]}

T-wave morphology is a powerful genotype clue. LQT1 produces a broad-based T wave, LQT2 a low-amplitude bifid or notched T wave, and LQT3 a long isoelectric ST segment followed by a late-onset T wave. For Brugada, look for the three patterns in the right precordial leads: type 1 (coved ST elevation of 2 mm or more followed by a negative T wave — the only diagnostic pattern), type 2 (saddle-back, with J-point elevation generally 2 mm or more in V2 and terminal ST elevation of at least 0.5 mm, followed by a positive T wave in V2), and type 3 (saddleback or coved with ST elevation under 1 mm). For ERS, look for J-point elevation over 0.1 mV with a notched or slurred terminal QRS in the inferior or lateral leads. For SQTS, a QTc of 320 ms or less should prompt the diagnosis, and a QTc of 360 ms or less counts with a pathogenic variant or family history; across 61 published cases the mean QTc was 307 ms (range 248 to 381 ms).^{[11][12][20][29]}

The Schwartz score (Schwartz et al. 1993, updated by Schwartz and Crotti in 2011) is a formal diagnostic instrument that integrates ECG, clinical history, and family history to assign probability of LQTS. It is the standard framework for diagnosing LQTS when the genotype is unknown and should be reproduced exactly.^[2][26]

Provocative testing is used when the resting ECG is non-diagnostic. The exercise stress test has two roles: it can reveal paradoxical QT prolongation during early recovery in LQT1, and it is the diagnostic test for CPVT — provoking bidirectional or polymorphic VT reproducibly at a heart rate of 100 to 130 bpm. Adrenaline infusion (a graded epinephrine challenge) unmasks concealed LQT1 by paradoxically prolonging the QTc. Ajmaline or flecainide challenge (a sodium-channel blocker infusion) is used to unmask a Brugada pattern in patients with type 2 or 3 ECGs or a family history — but is reserved for specialised units because it can provoke VF. Holter monitoring (24 to 48 hours) captures paroxysmal arrhythmia and quantifies heart rate response to exercise. Echocardiography is performed in every case to exclude structural heart disease (HCM, ARVC, myocarditis) and to confirm the structurally normal heart that defines the channelopathies.^[1][7]

Genetic testing is now standard and uses a panel covering KCNQ1, KCNH2, SCN5A, KCNE1, KCNE2, KCNJ2, CACNA1C, ANK2, RYR2, CASQ2, and others. Roughly 75 percent of clinically definite LQTS is explained by a pathogenic variant in one of 15 known genes, so 20 to 25 percent of families meeting clinical criteria have no detectable variant; in Brugada syndrome SCN5A accounts for 18 to 28 percent of cases. A positive result enables cascade screening of relatives (cascade testing of first-degree relatives with ECG, exercise test, and targeted genetic testing for the proband's mutation). A negative result does not exclude the diagnosis — phenotype-positive/genotype-negative relatives are still treated as at risk of sudden death and need clinical follow-up.^[4][12][28]

Management — Resuscitation

Enlarge

The acute management of torsades de pointes or ventricular fibrillation in a channelopathy patient follows a standardised bundle that combines arrhythmia termination with correction of the precipitant.^[3]

^{[19] [24]}

Management — Definitive & Stepwise

Definitive management combines lifestyle modification, beta-blockade, device therapy, and adjunctive pharmacology, individualised by syndrome and risk.^[1][5]

Lifestyle modification applies to every channelopathy patient. Avoid all QT-prolonging drugs (consult CredibleMeds before any new prescription). Avoid competitive and high-intensity sport — especially swimming in LQT1, all competitive sport in CPVT and symptomatic Brugada. Avoid dehydration and electrolyte depletion. Avoid sudden loud auditory stimuli (turn off alarm clocks, telephones, and doorbells at night) in LQT2. Treat fever aggressively (paracetamol, cooling) in Brugada. Avoid alcohol excess and large meals in Brugada. Provide genetic counselling and family planning. ^[1]

Beta-blockade is first-line for LQTS and CPVT. In 869 LQTS patients, beta-blockers reduced the cardiac-event rate in probands from 0.97 to 0.31 events per patient-year, a significant reduction overall — but prior symptoms predicted breakthrough: 32 percent of previously symptomatic patients had another cardiac event within 5 years on therapy, and 14 percent of those with a prior aborted cardiac arrest had another arrest within 5 years on treatment.^[5] Not all beta-blockers are equal: among 382 LQT1/LQT2 patients, symptomatic patients started on metoprolol had a nearly four-fold higher risk of breakthrough cardiac events than users of the other two agents combined (odds ratio 3.95, 95 percent CI 1.2 to 13.1), propranolol shortened the QTc significantly more than either metoprolol or nadolol, and propranolol and nadolol were equally effective — metoprolol should not be used for symptomatic LQT1 and LQT2 patients.^[14] Response is genotype-dependent: freedom from recurrent events on beta-blockade was highest in LQT1 (81 percent), intermediate in LQT2 (59 percent), and lowest in LQT3 (50 percent, with a 17 percent death rate).^[13] In CPVT, the estimated 8-year event rate was 27 percent with beta-blockers versus 58 percent without, and absence of beta-blockade was an independent predictor of cardiac events (hazard ratio 5.48, 95 percent CI 1.80 to 16.68).^[6]

^{[14] [6]}

ICD therapy is indicated for secondary prevention in every patient who has survived a cardiac arrest or documented VT/VF — a class I recommendation in the J-wave syndromes — and for primary prevention in high-risk phenotypes: LQTS with recurrent syncope or beta-blocker-resistant symptoms despite therapy; symptomatic spontaneous type 1 Brugada in whom syncope was likely arrhythmic (class IIa, decided case by case by an experienced electrophysiologist); asymptomatic Brugada patients with inducible VF at programmed stimulation (class IIb, and inducibility was not predictive of events in the FINGER registry); CPVT with breakthrough events on beta-blocker plus flecainide; and SQTS with symptoms or family history of SCD. The ICD does not prevent the arrhythmia — it terminates it — and is reserved for those in whom pharmacological and lifestyle measures are inadequate.^{[1][12][23][28]}

Adjunctive and alternative therapies are used when beta-blocker plus ICD are inadequate or inappropriate: ^[1]

• Left cardiac sympathetic denervation (LCSD) — surgical removal of cardiac adrenergic input, reserved for patients who continue to have events despite beta-blockers. In 147 high-risk LQTS patients (99 percent symptomatic, 48 percent with a prior cardiac arrest, 75 percent still symptomatic on beta-blockers), LCSD cut the mean yearly number of cardiac events per patient by 91 percent, left 46 percent asymptomatic, reduced sudden death to 7 percent, and cut ICD shock counts by 95 percent in patients with recurrent shocks; a post-LCSD QTc under 500 ms predicted very low risk.^[15]
• Sodium-channel blockers — mexiletine 6 to 8 mg/kg/day is gene-specific therapy for LQT3; the degree of QTc shortening and the protection achieved vary with the SCN5A mutation, because mexiletine-sensitive and mexiletine-insensitive mutations have different gating properties.^[16]
• Quinidine — in 25 patients with Brugada syndrome and inducible VF, quinidine (mean dose 1483 mg daily) prevented VF induction in 22 (88 percent), with no arrhythmic events on long-term follow-up; it is an adjunct or potential alternative to ICD in high-risk Brugada patients.^[18]
• Flecainide — blocks the cardiac ryanodine receptor (RyR2) directly and prevents exercise-induced CPVT in mice and humans; among class I antiarrhythmics only flecainide and propafenone inhibit RyR2 channels.^[21]

Specific Subtypes & Scenarios

Each channelopathy has its own high-yield clinical pearl set. ^[1]

LQT1 — exercise and swimming triggered; broad-based T wave; the best beta-blocker response of the three major genotypes (81 percent of LQT1 patients free of recurrent events on therapy, death rate 4 percent); ICD for syncope despite beta-blocker or a QTc of 500 ms or more. The most common genotype and the one most reliably controlled by beta-blockade. ^[1][13]

LQT2 — events cluster away from exercise: 29 percent at rest or sleep, and emotion is a recognised trigger; beta-blocker response is intermediate (59 percent event-free). The postpartum period is a time of increased arrhythmogenic susceptibility, and LQT2 mutations were found in 13 of 14 patients (93 percent) with a personal or family history of postpartum cardiac events.^[13][17]

LQT3 — rest and sleep triggered, bradycardia-dependent; long isoelectric ST; the weakest beta-blocker response (50 percent event-free, 17 percent death rate); mexiletine 6 to 8 mg/kg/day shortens the QT in mexiletine-sensitive SCN5A mutations; ICD often required. Competitive sport is still avoided. ^[1][13][16]

Jervell-Lange-Nielsen syndrome (recessive KCNQ1 or KCNE1) — congenital sensorineural deafness; very long QTc; high risk of early SCD; ICD often required in childhood. Andersen-Tawil (LQT7, KCNJ2) — periodic paralysis, dysmorphic facies, bidirectional VT, mild QT prolongation with prominent U waves. Timothy (LQT8, CACNA1C) — syndactyly, autism, congenital heart disease, very long QT; high mortality in infancy.^[1]

Brugada syndrome — only proven therapy is ICD. Quinidine and isoproterenol are adjunctive for arrhythmia storm. Treat fever aggressively (fever unmasks and worsens the ECG and triggers VF). Avoid all sodium-channel blockers (check brugadadrugs.org). No competitive sport if symptomatic. Asymptomatic patients make up about 63 percent of new diagnoses and their risk of developing symptoms is about 0.5 percent per year; note that inducibility of VT/VF at electrophysiology study did not predict events in the 1,029-patient FINGER registry, so a "negative EP study" is not the reassurance it is often taught to be.^[7][12][23]

CPVT — nadolol is first-line and reduces events dramatically; flecainide is added for breakthrough (reduces bidirectional VT burden); left cardiac sympathetic denervation for breakthrough on combination therapy; ICD for survivors of cardiac arrest or sustained VT despite maximal therapy. All competitive sport is contraindicated. The diagnosis is exercise-induced; the resting ECG is normal, so the exercise test is mandatory in any child with exercise-induced syncope.^[6]

SQTS — ICD is the only proven therapy; quinidine may be used to prolong QT and reduce events. Atrial fibrillation is common and may be the presentation. Programming the ICD is technically challenging because the short QT can be misinterpreted as a T wave and lead to inappropriate shocks.^[10]

ERS — most early repolarisation patterns are benign and require no treatment. The syndrome is defined by idiopathic VF or family history of SCD plus J-point elevation in the inferior or lateral leads. Survivors of cardiac arrest receive an ICD; quinidine and isoproterenol are adjunctive.^[11][12] ERS subtypes and risk stratification — the Antzelevitch 2016 J-wave consensus distinguishes type I ERS (J-point elevation localised to the lateral leads), type II (inferolateral), and type III (inferolateral plus anterior or right ventricular leads, i.e. global, and the highest risk). High-risk ERS features include J-point elevation of 0.2 mV or more, a horizontal or descending ST segment (rather than an ascending one), dynamic changes in J-point elevation, and a history of arrhythmic syncope or family SCD — these are precisely the items weighted in the proposed Shanghai ERS score. In the Finnish population cohort, inferior J-point elevation of 0.1 mV or more carried a relative risk of 1.43 for arrhythmic death, rising to 2.92 when the J-point elevation reached 0.2 mV; a J wave with a horizontal or descending ST segment predicted sudden death (RR 1.43) while the upsloping variant did not.^[12]

Complications & Pitfalls

Disease-related complications include recurrent torsades de pointes and ventricular fibrillation despite therapy, cardiac arrest, and sudden cardiac death. Beta-blockade cut the proband event rate from 0.97 to 0.31 events per patient-year, yet breakthrough remains real — 32 percent of previously symptomatic patients have another cardiac event within 5 years on therapy — and untreated congenital LQTS has been reported to carry a mortality of more than 50 percent over 5 years.^[5][24]

ICD-related complications are common and important: pocket infection, lead fracture or displacement, inappropriate shocks (often from T-wave oversensing in LQTS or sinus tachycardia in CPVT), device malfunction, and the psychological burden of living with a device (anxiety, depression, body-image concerns, driving restrictions). In children, lead failure is the dominant long-term complication and may require extraction. Left cardiac sympathetic denervation can cause Horner syndrome (usually mild and transient) and post-syndetic neuralgia. ^[1]

The classic diagnostic pitfalls are: (1) misdiagnosing LQTS syncope as epilepsy for years before an ECG is checked; (2) failing to measure QTc manually — automated reports are unreliable, particularly in LQT2 with notched T waves; (3) prescribing a QT-prolonging drug (especially a macrolide, ondansetron, or antipsychotic) to an LQTS patient without checking CredibleMeds; (4) diagnosing Brugada on a type 2 or 3 ECG without provocation testing or family evaluation; (5) treating CPVT with a beta-1 selective agent (metoprolol) instead of nadolol — metoprolol is insufficient; (6) missing the diagnosis of CPVT because the resting ECG is normal and an exercise test was not done.^[1][6]

Prognosis & Disposition

Prognosis depends on genotype, QTc duration, history of syncope or cardiac arrest, age at first event, and response to therapy. LQT1 has the best prognosis on beta-blocker (81 percent event-free) and the lowest first-event rate before age 40 (30 percent, versus 46 percent for LQT2 and 42 percent for LQT3). LQT3 has the highest death rate on beta-blockade (17 percent), and QTc is not an independent predictor within LQT3, where sex is. LQT2 confers increased risk in the 9-month postpartum period; in Brugada, the FINGER registry cardiac-event rate was 7.7 percent per year after aborted sudden death, 1.9 percent per year after unexplained syncope, and 0.5 percent per year in asymptomatic patients. CPVT has high mortality if untreated but is well controlled on nadolol plus flecainide; SQTS carries an early SCD risk and ICD is the only proven therapy.^{[8][13][22][23]}

Disposition is outpatient for asymptomatic patients on stable therapy (annual cardiology review with ECG, exercise test, and ICD interrogation as appropriate), inpatient for a new diagnosis with syncope or after cardiac arrest (for risk stratification, ICD implantation, or LCSD), and ITU/CCU for ongoing TdP or VF, electrical storm, or post-arrest stabilisation. Genetic counselling and cascade screening of first-degree relatives (ECG, exercise test, targeted genetic testing) must be initiated from the index case.^[4]

Special Populations

Pregnancy: continue beta-blocker throughout pregnancy — never discontinue. Pregnancy itself was associated with a reduced risk of cardiac events (hazard ratio 0.28), but the 9-month postpartum period carried a hazard ratio of 2.7, highest in LQT2; beta-blocker use during that window reduced events (hazard ratio 0.34), so peripartum monitoring and dose optimisation are essential. Vaginal delivery is generally preferred; epidural anaesthesia is acceptable but avoid hypotension and electrolyte shifts. Genetic counselling before pregnancy is recommended.^[1][22]

Paediatric: the Schwartz score is valid in children; therapy is identical with weight-based dosing. In 3,015 LQTS children followed from 1 to 12 years, boys had a significantly higher cumulative probability of aborted cardiac arrest or sudden death than girls (5 percent versus 1 percent); a QTc over 500 ms (hazard ratio 2.72) and prior syncope identified risk in boys, whereas prior syncope was the only significant risk factor in girls, and beta-blocker therapy reduced the risk of life-threatening events by 53 percent. Activity restriction must be balanced against the developmental importance of play. ICD implantation in small children is technically challenging and LCSD may be preferred as a temporising strategy.^[9]

Athletes: LQT1 carries the highest risk of exercise-induced events of the LQTS subtypes, and historically all these patients were discouraged from sport on low-quality evidence. Contemporary data are more reassuring: in one return-to-play cohort of 494 LQTS patients the event rate was 1.16 non-lethal events per 100 athlete-years, most breakthrough events were not sport-related, and in a separate 352-patient series no sport-related cardiac event occurred over 650 patient-years — with medication adherence the dominant protective factor. Recommendations have accordingly shifted from blanket disqualification to shared decision-making in a specialist inherited-arrhythmia centre, with exercise testing as part of the pre-participation assessment (a negative test is not reassurance, because emotional stress also triggers events) and an AED available at the sporting venue. Competitive sport remains restricted in CPVT and in symptomatic Brugada. ^[1][30]

Elderly: the elderly more often have acquired than congenital LQTS — focus on drug review (especially polypharmacy with antibiotics, antipsychotics, and antiarrhythmics) and electrolyte disturbance. Baseline QTc is mildly longer in older women. ^[1]

Family: cascade screening is mandatory. Offer ECG and exercise testing to all first-degree relatives of a confirmed case; if the proband has an identified mutation, offer targeted genetic testing. Genetic counselling before reproductive decisions is standard.^[4]

Evidence, Guidelines & Regional Differences

The 2013 HRS/EHRA/APHRS expert consensus on inherited primary arrhythmia syndromes (Priori et al., PMID 24011539) is the unifying international document and the most frequently cited reference for diagnosis and management. It is supplemented by the 2015 ESC guidelines on ventricular arrhythmias and SCD, the 2017 AHA/ACC/HRS ventricular arrhythmia guideline, the 2006 ACC/AHA/ESC guidelines (Zipes et al., PMID 16935995), and — for sport — the 2024 HRS consensus statement on arrhythmias in athletes; the class-of-recommendation statements reproduced on this page are taken from the 2016 J-wave syndromes consensus (PMID 27423412), which is the document quoted here.^{[1][3][12][30]}

The Schwartz diagnostic score (Schwartz 1993, PMID 8339437; updated by Schwartz and Crotti 2011, PMID 22083145) remains the standard diagnostic instrument for clinically suspected LQTS. The Moss 2000 cohort of 869 patients (PMID 10673253) established that beta-blockade cuts the proband cardiac-event rate from 0.97 to 0.31 events per patient-year, without stratifying by genotype; the genotype-specific efficacy figures come from Schwartz 2001 (PMID 11136691). The Priori 2003 risk-stratification paper (PMID 12736279) quantified genotype-specific risk and informed the modern ICD strategy. The Goldenberg 2008 paediatric study (PMID 18427136) identified a QTc over 500 ms and prior syncope as the risk factors in boys, and prior syncope alone in girls. The Antzelevitch 2005 second consensus on Brugada (PMID 15898165) and the 2016 J-wave syndromes consensus (PMID 27423412) frame ERS. The Hayashi 2009 CPVT cohort (PMID 19398665) defined the natural history and risk factors, and the FINGER registry (PMID 20100972) supplies the Brugada event rates.^{[2][5][6][7][8][9][12][13][23][26]}

Regional deltas are small but worth knowing: brugadadrugs.org (Antzelevitch group) and CredibleMeds (Arizona CERT) are the practical international references for drug avoidance; and the type 1 Brugada ECG is far commoner in East and Southeast Asia — 0.15 to 0.27 percent of Japanese adults and 0.18 percent of Filipinos — which is why sudden unexplained nocturnal death syndrome in that region is regarded as the same entity as Brugada syndrome. ^[1][12]

Exam Pearls

• LQT1: events during exercise (62 percent of events); best beta-blocker response (81 percent event-free).^[13]
• LQT2: events at rest or sleep and with emotion, not exercise; LQT2 underlies the great majority of postpartum cardiac events.^[13][17]
• LQT3: events at rest or sleep (39 percent); weakest beta-blocker response (50 percent event-free, 17 percent death rate); mexiletine 6 to 8 mg/kg/day is the gene-specific add-on.^[13][16]
• CPVT: stress-induced arrhythmia of exertion or emotion; beta-blockers cut the 8-year event rate from 58 to 27 percent.^[6]
• Brugada: ICD is considered the only effective treatment for high-risk patients; quinidine prevented inducible VF in 88 percent and is the adjunctive drug.^[18]
• SQTS: reported QTc in 61 published cases averaged 307 ms (range 248 to 381 ms); formal diagnostic criteria now exist, and index events (sudden death, aborted arrest, syncope, atrial fibrillation) had occurred in 57 percent before diagnosis.^[20]
• QTc of 500 ms or more is an independent predictor of risk in LQT1 and LQT2 — the threshold that changes management.^[8]
• Acute TdP: magnesium sulfate 2 g by slow IV push, then 1 to 4 g/hour titrated to a magnesium above 2 mmol/L and stopped above 3 mmol/L — with levels checked, because toxicity above 3.5 mmol/L causes respiratory depression, coma and arrest; correct hypokalaemia and hypomagnesaemia (target K+ 4.5 to 5 mmol/L); accelerate the heart rate with overdrive pacing for pause-dependent torsades — isoproterenol only when the long QT is acquired, since it is contraindicated in congenital LQTS.^[19][24]
• Review every drug a long-QT patient takes — type Ia antiarrhythmics and many other agents precipitate torsades.^[19]
• Screen relatives: formal diagnostic criteria were developed precisely so that at-risk family members can be screened after an index case.^[20]

Exam application bank (NEET-PG / INICET)

One-line answer

Long QT syndrome and the related cardiac channelopathies (Brugada, CPVT, short QT, early repolarisation) are inherited arrhythmia syndromes caused by mutations in cardiac ion-channel genes that predispose young, structurally normal hearts to syncope, torsades de pointes, ventricular fibrillation and sudden cardiac death. The dominant therapy is beta-blockade (nadolol or propranolol for LQTS and CPVT), avoidance of QT-prolonging drugs, lifestyle modification, and ICD implantation for secondary prevention or high-risk primary prevention. Acute torsades de pointes is treated with a slow 2 g IV magnesium push, defibrillation if pulseless or sustained, and rate acceleration by overdrive pacing for pause-dependent forms - isoprenaline is reserved for acquired long QT because it can lengthen the QT further in congenital LQTS. ^[1][24]

Worked stems (answer without another resource)

Stem 1 — Classic presentation. Map symptoms to mechanism; name the first investigation and first treatment step with dose/route if drug therapy is standard. ^[1]

Stem 2 — Unstable / complicated. List red flags that force immediate resuscitation, theatre, ICU, antidote, or reperfusion — and what you do in the first 15 minutes. ^[1]

Stem 3 — Atypical group. Elderly, pregnancy, child, or immunocompromised: how presentation and thresholds change. ^[1]

Stem 4 — Differential trap. Name the three closest mimics and one discriminator for each. ^[1]

Stem 5 — Disposition. Who goes home with safety-netting, who is admitted, who needs HDU/ICU/theatre, and what follow-up is mandatory. ^[1]

Rapid viva checklist

1. Definition + classification
2. Pathophysiology chain
3. Bedside signs / criteria
4. Score with exact components (if any)
5. Emergency bundle
6. Definitive therapy with doses
7. Complications of disease and of treatment
8. Special populations
9. Guideline/trial name if classic
10. Three exam traps

Coverage self-check

If you cannot answer any stem above from this page alone, re-read the matching section — the page is intended to be self-sufficient for final-prof and NEET-PG/INICET questions on Long QT and Channelopathies.

The mantra, and the ward-round test

^{[5] [8] [13] [19] [24]}

The mantra: a young patient with syncope and a normal echo is a channelopathy until the ECG and the family tree prove otherwise — and the circumstance of the collapse names the gene.^[1][6]

Ward-round test — three stems, thirty seconds each

Stem 1 — the swimmer whose collapse was called a seizure (answer)ShowHide

The 14-year-old from the top of the topic. Her resting QTc is 520 ms, echo normal. What is the genotype, and what do you do? Model: Syncope during swimming with a long QTc points to LQT1 — a loss-of-function mutation in KCNQ1 (the IKs current). Start nadolol (the preferred long-acting non-selective beta-blocker), restrict swimming and high-intensity exertion, refer to electrophysiology, and cascade-screen the family (ECG, genetic testing for the proband's mutation). The "seizure" label is the trap — there was no aura, no post-ictal state, and a family history of sudden death; this is cerebral hypoperfusion from torsades, not epilepsy.^[1][5]

Stem 2 — torsades on the ward (answer)ShowHide

A 72-year-old inpatient on IV haloperidol for delirium, with chronic kidney disease and a potassium of 3.1, develops a polymorphic tachycardia with a QRS that twists around the baseline. The QTc is 560 ms. What is the rhythm and what is the first drug? Model: This is torsades de pointes from an acquired long QT — a QT-prolonging drug compounded by hypokalaemia, hypomagnesaemia, and bradycardia, the three classic precipitants. The first drug is intravenous magnesium sulfate, which abolishes torsades without aggravating it. Stop the culprit drug, replace potassium and magnesium, and if the rhythm is pause-dependent and recurrent, accelerate the heart rate with an isoprenaline infusion or cardiac pacing. Defibrillate if sustained or pulseless.^[19]

Stem 3 — the child who collapses in PE (answer)ShowHide

A 9-year-old boy collapses during a school cross-country, recovers fully, and his resting 12-lead ECG is entirely normal, QTc 410 ms. His GP calls it vasovagal. What is the likely diagnosis, and what test must you do? Model: Exercise- or emotion-induced syncope with a structurally normal heart and a normal resting ECG is catecholaminergic polymorphic ventricular tachycardia (CPVT) until proven otherwise — a ryanodine-receptor (RYR2) mutation causing diastolic calcium leak under adrenergic stress. The exercise stress test is mandatory and diagnostic — it provokes bidirectional or polymorphic VT reproducibly at a heart rate of 100 to 130 bpm. Start nadolol immediately, restrict all competitive sport, add flecainide for breakthrough, and consider left cardiac sympathetic denervation or an ICD for refractory disease. The normal resting ECG is the trap that makes every CPVT child a "seizure" first.^[1][6]

References30ShowHide

1. [1]Priori SG, Wilde AA, Horie M, et al. HRS/EHRA/APHRS expert consensus statement on the diagnosis and management of patients with inherited primary arrhythmia syndromes: document endorsed by HRS, EHRA, and APHRS in May 2013 and by ACCF, AHA, PACES, and AEPC in June 2013 Heart Rhythm, 2013.PMID 24011539
2. [2]Schwartz PJ, Moss AJ, Vincent GM, Crampton RS Diagnostic criteria for the long QT syndrome. An update Circulation, 1993.PMID 8339437
3. [3]Zipes DP, Camm AJ, Borggrefe M, et al. ACC/AHA/ESC 2006 Guidelines for Management of Patients With Ventricular Arrhythmias and the Prevention of Sudden Cardiac Death: a report of the American College of Cardiology/American Heart Association Task Force and the European Society of Cardiology Committee for Practice Guidelines (writing committee to develop Guidelines for Management of Patients With Ventricular Arrhythmias and the Prevention of Sudden Cardiac Death): developed in collaboration with the European Heart Rhythm Association and the Heart Rhythm Society Circulation, 2006.PMID 16935995
4. [4]Ackerman MJ, Priori SG, Willems S, et al. HRS/EHRA expert consensus statement on the state of genetic testing for the channelopathies and cardiomyopathies: this document was developed as a partnership between the Heart Rhythm Society (HRS) and the European Heart Rhythm Association (EHRA) Europace, 2011.PMID 21810866
5. [5]Moss AJ, Zareba W, Hall WJ, et al. Effectiveness and limitations of beta-blocker therapy in congenital long-QT syndrome Circulation, 2000.PMID 10673253
6. [6]Hayashi M, Denjoy I, Extramiana F, et al. Incidence and risk factors of arrhythmic events in catecholaminergic polymorphic ventricular tachycardia Circulation, 2009.PMID 19398665
7. [7]Antzelevitch C, Brugada P, Borggrefe M, et al. Brugada syndrome: report of the second consensus conference Heart Rhythm, 2005.PMID 15898165
8. [8]Priori SG, Schwartz PJ, Napolitano C, et al. Risk stratification in the long-QT syndrome N Engl J Med, 2003.PMID 12736279
9. [9]Goldenberg I, Moss AJ, Zareba W, et al. Risk factors for aborted cardiac arrest and sudden cardiac death in children with the congenital long-QT syndrome Circulation, 2008.PMID 18427136
10. [10]Brugada R, Hong K, Dumaine R, et al. Sudden death associated with short-QT syndrome linked to mutations in HERG Circulation, 2004.PMID 14676148
11. [11]Haïssaguerre M, Derval N, Sacher F, et al. Sudden cardiac arrest associated with early repolarization N Engl J Med, 2008.PMID 18463377
12. [12]Antzelevitch C, Yan GX, Ackerman MJ, et al. J-Wave syndromes expert consensus conference report: Emerging concepts and gaps in knowledge Heart Rhythm, 2016.PMID 27423412
13. [13]Schwartz PJ, Priori SG, Spazzolini C, et al. Genotype-phenotype correlation in the long-QT syndrome: gene-specific triggers for life-threatening arrhythmias Circulation, 2001.PMID 11136691
14. [14]Chockalingam P, Crotti L, Girardengo G, et al. Not all beta-blockers are equal in the management of long QT syndrome types 1 and 2: higher recurrence of events under metoprolol J Am Coll Cardiol, 2012.PMID 23083782
15. [15]Schwartz PJ, Priori SG, Cerrone M, et al. Left cardiac sympathetic denervation in the management of high-risk patients affected by the long-QT syndrome Circulation, 2004.PMID 15051644
16. [16]Ruan Y, Liu N, Bloise R, et al. Gating properties of SCN5A mutations and the response to mexiletine in long-QT syndrome type 3 patients Circulation, 2007.PMID 17698727
17. [17]Khositseth A, Tester DJ, Will ML, et al. Identification of a common genetic substrate underlying postpartum cardiac events in congenital long QT syndrome Heart Rhythm, 2004.PMID 15851119
18. [18]Belhassen B, Glick A, Viskin S Efficacy of quinidine in high-risk patients with Brugada syndrome Circulation, 2004.PMID 15381640
19. [19]Banai S, Tzivoni D Drug therapy for torsade de pointes J Cardiovasc Electrophysiol, 1993.PMID 8269292
20. [20]Gollob MH, Redpath CJ, Roberts JD The short QT syndrome: proposed diagnostic criteria J Am Coll Cardiol, 2011.PMID 21310316
21. [21]Hwang HS, Hasdemir C, Laver D, et al. Inhibition of cardiac Ca2+ release channels (RyR2) determines efficacy of class I antiarrhythmic drugs in catecholaminergic polymorphic ventricular tachycardia Circ Arrhythm Electrophysiol, 2011.PMID 21270101
22. [22]Seth R, Moss AJ, McNitt S, et al. Long QT syndrome and pregnancy J Am Coll Cardiol, 2007.PMID 17349890
23. [23]Probst V, Veltmann C, Eckardt L, et al. Long-term prognosis of patients diagnosed with Brugada syndrome: Results from the FINGER Brugada Syndrome Registry Circulation, 2010.PMID 20100972
24. [24]Cohagan B, Brandis D Torsade de Pointes StatPearls, 2026.PMID 29083738
25. [25]Frommeyer G, Fischer C, Ellermann C, et al. Severe Proarrhythmic Potential of the Antiemetic Agents Ondansetron and Domperidone Cardiovasc Toxicol, 2017.PMID 28185059
26. [26]Schwartz PJ, Crotti L QTc behavior during exercise and genetic testing for the long-QT syndrome Circulation, 2011.PMID 22083145
27. [27]Ji L, Yang S, Wang Q, et al. Clinical and genetic analysis of pediatric catecholaminergic polymorphic ventricular tachycardia: focus on sinus bradycardia and neurodevelopmental disorders Front Pediatr, 2026.PMID 42290763
28. [28]Al-Akchar M, Siddique MS Long QT Syndrome StatPearls, 2026.PMID 28722890
29. [29]Bagkaki A, Papagiannis J, Anastasakis A, et al. Estimation of Incidence and Prevalence of Pediatric Channelopathies in a Mediterranean Population Based on a Single-Center, Retrospective Analysis Children (Basel), 2026.PMID 42194185
30. [30]Ertugrul I, Blom NA Sports or no sports? How to manage the young arrhythmia patient Herzschrittmacherther Elektrophysiol, 2025.PMID 40721681