What's long QT syndrome?
Long QT syndrome (LQTS) is a group of inherited heart-rhythm conditions in which the heart muscle takes too long to recover (repolarize) after each beat. This shows up on an ECG as a prolonged QT interval and raises the risk of dangerous arrhythmias, fainting, and sudden cardiac death. It is genetically diverse: different subtypes are defined by which channel gene is affected.
| Also indexed as | OMIM:192500, MONDO:0100316 |
|---|---|
| Features mapped | 9 |
| Treatments mapped | 6 |
| Published sources | 17 |
| Last reviewed | 2026-08-04 |
Signs and symptoms
Torsade de pointes
Torsades de pointes is a fast, dangerous rhythm of the heart's lower chambers that can arise in long QT syndrome. It can cause fainting and, if it does not stop on its own, can lead to sudden death.
Sudden cardiac death
Because the heart's electrical reset is delayed, long QT syndrome raises the risk of dangerous rhythms of the lower chambers, especially torsades de pointes. These rhythms can cause fainting, cardiac arrest, or sudden death, often triggered by physical or emotional stress.
Ventricular fibrillation
Ventricular fibrillation is a chaotic electrical disturbance in the heart's lower chambers that stops them from pumping blood. In long QT syndrome it is one of the rhythms that can lead to fainting and sudden death.
Prolonged QTc interval
The hallmark of long QT syndrome is a prolonged QTc interval on the ECG, reflecting delayed electrical recovery of the heart, which can set off the dangerous arrhythmia torsade de pointes.
Syncope
Syncope means fainting or a sudden, brief loss of consciousness. In long QT syndrome it can happen when a dangerous heart rhythm briefly interrupts blood flow to the brain, and it is often brought on by physical or emotional stress.
Prolonged QT interval
The defining feature of long QT syndrome is a prolonged QT interval. The QT interval is the part of the heartbeat, measured on an electrocardiogram (ECG), when the heart's lower chambers reset electrically between beats. In long QT syndrome this reset is delayed, so the QT interval is longer than normal.
Cardiac arrest
Cardiac arrest means the heart suddenly stops pumping effectively. In long QT syndrome it can result from a dangerous rhythm such as torsades de pointes, and it is often triggered by physical or emotional stress.
Notched T wave
In long QT syndrome type 2, the T wave, the part of the ECG tracing that reflects the heart's lower chambers resetting, can take on a characteristic abnormal shape. These T-wave changes have been described in children with this subtype.
Ventricular tachycardia
Long QT syndrome can trigger ventricular tachycardia, a fast, abnormal heart rhythm that may cause collapse.
How it is diagnosed
Long QT syndrome 1
Diagnosed using: Schwartz diagnostic score.
“…the diagnosis of long QT syndrome (LQTS) should not rely solely on QTc duration, but rather on a combination of findings, including QT prolongation, clinical features, and family history, as outlined by the Schwartz score.”
Long QT syndrome 1
Diagnosed using: exercise stress testing.
“Exercise stress testing can be useful to identify children who are gene positive borderline LQTS from a normal population and gene negative borderline QTc children, allowing for selective gene testing in a higher risk group of patients with borderline QTc intervals and intermediate Schwartz scores.”
Long QT syndrome 1
Diagnosed using: genetic testing of KCNQ1, KCNH2, and SCN5A.
“Diagnostic testing yield reached 75% in index patients; all causal variants were found in KCNQ1, KCNH2, and SCN5A genes.”
Long QT syndrome 1
Diagnosed using: 12-lead ECG QTc measurement.
“A markedly prolonged QTc (> 500 ms on at least two separate ECGs) strongly supports the diagnosis.”
Treatment and management
What the research describes, not a recommendation. Treatment decisions belong with your clinician.
This covers treatments that appear in the published research mapped here. Investigational and experimental therapies are not included, so their absence is a boundary of this map, not a sign they do not exist.
beta-blockers
Beta-blockers are the main, first-line treatment for long QT syndrome. They blunt the effect of adrenaline on the heart, which lowers the chance of a dangerous rhythm. They are not fully protective for everyone, so some people need additional measures.
Used to help with: Long QT syndrome 1.
“Beta-blockers remain the mainstay treatment.”
implantable cardioverter-defibrillator (ICD)
An implantable cardioverter-defibrillator (ICD) is a small device placed under the skin that watches the heart rhythm and delivers a shock to restore a normal beat if a life-threatening rhythm occurs. In long QT syndrome it is used for people at high risk and can reduce the risk of death.
Used to help with: Long QT syndrome 1.
“For high-risk patients, the implantable cardioverter-defibrillator (ICD) offer an effective therapeutic option to reduce mortality.”
left cardiac sympathetic denervation (LCSD)
Left cardiac sympathetic denervation (LCSD) is a surgical procedure that interrupts specific nerves carrying adrenaline-driven signals to the heart. By reducing those signals it lowers the chance of a dangerous rhythm, and it has been shown to help people with long QT syndrome.
Used to help with: Long QT syndrome 1.
“Left cardiac sympathetic denervation (LCSD) confers a strong antifibrillatory effect and provides significant therapeutic efficacy for patients with genetic heart diseases, especially long QT syndrome (LQTS) and catecholaminergic polymorphic ventricular tachycardia (CPVT).”
lifestyle modification and exercise restriction
Lifestyle measures are part of managing long QT syndrome. These include avoiding competitive exercise, since intense exertion can trigger dangerous rhythms in some people, alongside other adjustments tailored to the individual.
Used to help with: Long QT syndrome 1.
“Prohibition of competitive exercise and avoidance of QT-prolonging drugs are important issues in life-style modification.”
avoidance of QT-prolonging drugs
Certain medicines can lengthen the QT interval further, so avoiding QT-prolonging drugs is an important part of managing long QT syndrome. Keeping a list of medicines to avoid helps lower the risk of a dangerous rhythm.
Used to help with: Long QT syndrome 1.
“Prohibition of competitive exercise and avoidance of QT-prolonging drugs are important issues in life-style modification.”
mexiletine (for long QT syndrome type 3)
Mexiletine is a medicine that blocks sodium channels in the heart. It has shown benefit in long QT syndrome type 3, the subtype driven by a sodium-channel problem, where it can help shorten the prolonged QT interval.
Used to help with: Long QT syndrome 1.
“Mexiletine is a well-known sodium channel blocker, with proven efficacy in patients with sodium channel-mediated long QT syndrome type 3.”
Triggers to avoid
In this condition, certain drugs, foods, or other exposures can set off an acute episode in people who are affected, even when they are otherwise well. The research mapped here describes the agents below. This is information, not a recommendation: what to avoid and what is safe for any individual is a conversation for their own care team.
QT-prolonging drugs
Many common medications further prolong the QT interval and can trigger dangerous arrhythmias in people who are already susceptible. Avoiding QT-prolonging drugs is a core part of staying safe; what to avoid for any individual is a conversation for their care team.
Reported in the research mapped here as able to provoke: Torsade de pointes in people with this condition.
“Cardiac toxicity from QT-prolonging drugs can precipitate malignant ventricular arrhythmias in susceptible individuals, and family screening may clarify inherited risk.”
What changes how it shows up
Carrying the genetic change is not the whole story. The factors below are described in the research mapped here as changing whether, or how strongly, the condition appears. They modulate how the genotype is expressed; they do not, on their own, cause or cure it.
variable penetrance
Penetrance varies: carrying a disease-linked gene change does not, by itself, mean a person has a prolonged QT or symptoms. Within one family, some members carry the change with little sign of it while others are affected.
Described as modulating: Long QT syndrome 1.
“In addition, family members are presented to demonstrate the variable penetrance that is commonly seen.”
genotype-negative long QT
Genetic testing is not the whole story. About 15 to 20 percent of people clinically diagnosed with long QT syndrome have no identifiable gene change, so a negative genetic test does not rule the condition out. Diagnosis rests on the clinical picture and ECG, not on genetics alone.
Described as modulating: Long QT syndrome 1.
“Approximately 15% to 20% of patients clinically diagnosed with long QT syndrome (LQTS) are genotype-negative (GEN-).”
How to read the evidence labels
Where this comes from
This guide is built from 17 published source(s). Every claim above links back to one of them. Click any source ID to read the original on PubMed.
Take it further
Printed, source-linked documents built from this condition's graph — ready to bring to an appointment or attach to a coverage request. Every claim carries its published source, the same as this guide.