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Long QT Syndrome
editor
May 7, 2025
5:13 am
Long QT Syndrome (LQTS) is a disorder of the electrical system that triggers the heartbeat, and regulates the muscle contractions that pump the body's blood supply. There are two types of LQTS:
Table of Contents
The QT Interval
Medications and the QT Interval
Acquired LQTS is caused by certain medications.
Inherited LQTS is caused by a genetic mutation that can be passed down from generation to generation. (We now know that acquired LQTS may be due to the inheritance of less severe genetic abnormalities that are made worse by environmental factors such as medications or electrolyte abnormalities)
It is not known exactly how many people have LQTS, but the inherited type is thought to be a common cause of sudden, unexplained death in children and young adults.

The QT Interval

ECG, color photoMost people are familiar with electrocardiography (ECG or EKG), a test in which electrodes are temporarily attached onto the chest, arms and legs to record the heart's electrical activity. The electrodes send information to a machine that records and prints a "picture" (an electrocardiogram) of the pattern, or rhythm, of the electrical impulses that pace the heart beat. Each impulse generates a heart beat. The line created for each beat on the ECG is called a "waveform."

ECG, B+W illustration

A waveform on an ECG represents the electrical activity of each heart beat.
The letters, P, Q, R, S, and T represent different parts of each waveform.
The Q-T interval, diagram The space between the beginning of the Q wave and the end of the T wave (called the QT Interval) is a critical juncture. It represents the time it takes for the heart's electrical system to recharge after each beat (a process called "repolarization") before generating the next signal to activate the ventricles, the major pumping chambers of the heart.
In Long QT Syndrome, the interval between Q and T is longer than normal. People with this syndrome are susceptible to an abnormally rapid heart rhythm (arrhythmia) called "torsade de pointes." When this occurs, the heart muscle cannot contract effectively, and the normal volume of blood is reduced to the body and - most important - to the brain. If the brain is starved of oxygen, the indivdiual faints within seconds. If the heart cannot regain its normal rhythm, it may go into spasms that lead to a deadly arrhythmia called ventricular fibrillation. Without immediate emergency treatment, death follows within minutes.
Fainting is the primary symptom - and may be the only warning sign - of LQTS. Once a person has been diagnosed with the LQTS, all family members should be tested, including the parents, siblings and children of the affected individual.
LQTS is caused by a dysfunction of cells in the heart called ion channels. Ions are "charged" particles found in substances such as sodium and potassium. It is the flow of ions in and out of the cells that produce the heart's electrical activity. Some medications may cause acquired LQTS. There are at least 50 or more FDA approved medications that are known to prolong the Q-T interval. This generally is not a problem and does not lead to torsades de pointes or other heart rhythm disorders for most people. These medications should be prescribed carefully, however, for people with some types of health problems. They must be avoided altogether by people who already have been diagnosed with LQTS. (Some of these medications may require monitoring in the hospital when they are started.) If you are taking any medications that cause dizziness, fainting, confusion or irregular heart rhythms, notify your doctor immediately.

Drugs that prolong the QT interval and/or induce Torsades De Pointes
The following list of drugs is derived from information found in the labeling of FDA-approved drugs, or in the medical literature. There may be other drugs and/or substances that also cause these heart rhythm problems that are not listed here.
Drug & Brand Names Drug Class (Clinical Use)
Arsenic trioxide (Trisenox�) Anti-cancer/Leukemia
Bepridil (Vascor�) Anti-anginal/heart pain
Chlorpromazine (Thorazine�) Anti-psychotic/Anti-emetic/schizophrenia/nausea
Cisapride (Propulsid�) GI stimulant/heartburn
Clarithromycin (Biaxin�) Antibiotic/bacterial infection
Disopyramide (Norpace�) Anti-arrhythmic/abnormal heart rhythm
Dofetilide (Tikosyn�) Anti-arrhythmic/abnormal heart rhythm
Dolasetron (Anzemet�) Anti-nausea/nausea, vomiting
Droperidol (Inapsine�) Sedative;Anti-nausea/anesthesia adjunct, nausea
Erythromycin (E.E.S.� ,Erythrocin�) Antibiotic;GI stimulant/bacterial infection; increase GI motility
Felbamate (Felbatrol�) Anti-convulsant/seizure
Fluoxetine (Prozac�,Sarafem�) Anti-depressant/depression
Foscarnet (Foscavir�) Anti-viral/HIV infection
Fosphenytoin (Cerebyx�) Anti-convulsant/seizure
Gatifloxacin (Tequin�) Antibiotic/bacterial infection
Halofantrine (Halfan�) Anti-malarial/malaria infection
Haloperidol (Haldol�) Anti-psychotic/schizophrenia, agitation
Ibutilide (Corvert�) Anti-arrhythmic/abnormal heart rhythm
Indapamide (Lozol�) Diuretic/stimulate urine & salt loss
Isradipine (Dynacirc�) Anti-hypertensive/high blood pressure
Levofloxacin (Levaquin�) Antibiotic/bacterial infection
Levomethadyl (Orlaam�) Opiate agonist/pain control, narcotic dependence
Mesoridazine (Serentil�) Anti-psychotic/schizophrenia
Moexipril/HCTZ (Uniretic�) Anti-hypertensive/high blood pressure
Moxifloxacin (Avelox�) Antibiotic/bacterial infection
Naratriptan (Amerge�) Serotonin receptor agonist/Migraine treatment
Nicardipine (Cardene�) Anti-hypertensive/high blood pressure
Octreotide (Sandostatin�) Endocrine/acromegaly, carcinoid diarrhea
Paroxetine (Paxil�) Anti-depressant/depression
Pentamidine (NebuPent�,Pentam�) Anti-infective/pneumocystis pneumonia
Pimozide (Orap�) Anti-psychotic/Tourette's tics
Procainamide (Procan� ,Pronestyl�) Anti-arrhythmic/abnormal heart rhythm
Quetiapine (Seroquel�) Anti-psychotic/schizophrenia
Quinidine (Cardioquin�, Quiniglute�) Anti-arrhythmic/abnormal heart rhythm
Risperidone (Risperdal�) Anti-psychotic/schizophrenia
Salmeterol (Serevent�) Sympathomimetic/asthma, COPD
Sertraline (Zoloft�) Anti-depressant/depression
Sotalol (Betapace�) Anti-arrhythmic/abnormal heart rhythm
Sparfloxacin (Zagam�) Antibiotic/bacterial infection
Sumatriptan (Imitrex�) Serotonin receptor agonist/Migraine treatment
Tacrolimus (Prograf�) Immunosuppressant/Immune suppression
Tamoxifen (Nolvadex�) Anti-cancer/breast cancer
Thioridazine(Mellaril�) Anti-psychotic/schizophrenia
Tizanidine (Zanaflex�) Muscle relaxant
Venlafaxine (Effexor�) Anti-depressant/depression
Ziprasidone(Geodon�) Anti-psychotic/schizophrenia
Zolmitriptan (Zomig�) Migraine treatment
Adapted with permission from the Arizona Center for Education and Research on Therapeutics
Category : heart disease & disorders

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