| Click the image to view an animation on Long QT Syndrome 
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Long QT Syndrome (LQTS) is a disorder of the heart’s electrical system, in which the heart muscle cells take longer than normal to recover electrically after each beat. There are two types of LQTS: inherited and acquired. People with inherited LQTS have an abnormal gene that controls the heart muscle protein that is responsible for electrical activity in the heart muscle cells. Other people have normal genes, but are taking a medication or combination of medications that interfere with these same heart muscle proteins and cause acquired long QT. Some people may have a minor genetic abnormality that does not cause obvious LQTS by itself, but they may be very sensitive to certain medications and be more prone to developing LQTS.
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
| Click the image to view an animation on an electrocardiogram 
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A waveform on an ECG represents the electrical activity of each heart beat.
Most 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 control the heart beat. The line created for each beat on the ECG is called a "waveform." The curves that are drawn on the ECG graph show when the heart chambers are being activated and also when they are recovering after each beat.
The letters, P, Q, R, S, and T represent different parts of each waveform.
The distance between the beginning of the Q wave and the end of the T wave (called the QT Interval) is a critical measurement. It represents the amount of time the heart's electrical system takes to recharge after each beat (repolarization). After the heart cells have repolarized, the next signal, or heartbeat, can be generated
In LQTS, the QT interval is longer than normal. People with LQTS are at risk of developing an abnormally rapid heart rhythm (arrhythmia) called "Torsades de Pointes." This dangerous arrhythmia happens when an electrical impulse triggers a new heartbeat before the ventricles have fully recovered from the previous beat (repolarized). When this occurs, the heart muscle begins to quiver, and cannot contract effectively. Blood is not pumped out to the body and - most important - to the brain. If the brain is starved of blood and oxygen, the indivdiual faints within seconds. If the heart does not return to a normal rhythm on its own, it may switch into deadly arrhythmia called ventricular fibrillation. Without immediate emergency treatment, death follows within minutes.
Fainting or syncope is the primary symptom - and may be the only warning sign - of LQTS. Once a person has been diagnosed with LQTS, all family members should be tested, including the parents, siblings and children of the affected individual. Testing may include taking ECG recordings, performing an exercise treadmill test, and/or sending blood for genetic testing to look for the presence of an abnormal gene that can cause LQTS.
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, particularly in people who are taking more than one of these medications, or in the setting of some other types of health problems. These medications must be avoided altogether by people who already have been diagnosed with LQTS.
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 |
