https://www.mayoclinic.org/diseases-conditions/long-qt-syndrome/symptoms-causes/syc-20352518
Long QT syndrome (LQTS) is a heart rhythm disorder that causes fast, chaotic heartbeats. The irregular heartbeats can be life-threatening. LQTS affects the electrical signals that travel through the heart and cause it to beat. Some people are born with changes in DNA that cause long QT syndrome. This is known as congenital long QT syndrome.

https://www.uptodate.com/contents/acquired-long-qt-syndrome-definitions-pathophysiology-and-causes
Long QT syndrome (LQTS) is a disorder of myocardial repolarization characterized by a prolonged QT interval on the electrocardiogram (ECG) ( waveform 1 ). This syndrome is associated with an increased risk of polymorphic ventricular tachycardia (VT) and a characteristic life-threatening cardiac arrhythmia also known as torsades de pointes (TdP

https://www.medicalnewstoday.com/articles/qt-prolongation
QT prolongation is a condition that affects the heart rhythm and can lead to sudden cardiac arrest. Learn about the factors that can cause it, how to diagnose it, and what treatment options are available.

https://my.clevelandclinic.org/health/diseases/17183-long-q-t-syndrome-lqts
Long QT syndrome is a heart condition that affects the electrical system and increases the risk of life-threatening arrhythmias. Learn about the types, causes, diagnosis and treatment options for this rare disorder.

https://www.mayoclinic.org/diseases-conditions/long-qt-syndrome/diagnosis-treatment/drc-20352524
In a prolonged QT interval, it takes longer than usual for the heart to recharge between beats. A prolonged QT interval can be seen on a heart test called an electrocardiogram. An ECG is the most common test used to diagnose long QT syndrome. It records the electrical signals in the heart and shows how fast or how slow the heart is beating.

https://litfl.com/qt-interval-ecg-library/
Learn how to measure and interpret the QT interval and corrected QT interval on ECG, and the causes and consequences of QT prolongation and shortening. See examples of QT abnormalities and their associated conditions.

https://www.webmd.com/heart-disease/long-qt-syndrome-overview
Long QT syndrome (LQTS) is a rare disorder where your heart takes longer than usual to recover after each beat. It can be inherited or acquired, and can cause fainting, fluttering, seizures, or sudden death. Learn how to diagnose and treat it.

https://en.wikipedia.org/wiki/Long_QT_syndrome
Long QT syndrome (LQTS) is a condition affecting repolarization (relaxing) of the heart after a heartbeat, giving rise to an abnormally lengthy QT interval. It results in an increased risk of an irregular heartbeat which can result in fainting, drowning, seizures, or sudden death. These episodes can be triggered by exercise or stress. Some rare forms of LQTS are associated with other symptoms

https://www.ncbi.nlm.nih.gov/books/NBK441860/
The QT interval on an electrocardiogram (ECG) represents the duration of the ventricular action potential, and this physiologically correlates with the duration of the ventricular depolarization and repolarization. Cardiac events and fatal arrhythmias may occur when the QT interval is prolonged either congenitally or through acquired causes.[1][2][3]

https://www.merckmanuals.com/professional/cardiovascular-disorders/arrhythmogenic-cardiac-disorders/long-qt-interval-syndromes
Learn about the causes, symptoms, diagnosis, and treatment of long QT interval syndromes, a group of genetic disorders that prolong ventricular action potential and increase the risk of arrhythmias. Find out how to prevent triggers, use beta blockers, and consider an implantable cardioverter-defibrillator.

https://www.nhs.uk/conditions/long-qt-syndrome/
Long QT syndrome is an inherited heart problem that affects how your heart beats and can cause fainting or fits. Learn about the causes, symptoms, treatments and how to live with this condition from the NHS website.

https://www.uptodate.com/contents/acquired-long-qt-syndrome-clinical-manifestations-diagnosis-and-management
Acquired long QT syndrome (LQTS) is a disorder of myocardial repolarization that can be induced by drugs or other factors. It can cause life-threatening ventricular tachycardia and requires prompt recognition and treatment.

https://www.cedars-sinai.org/health-library/diseases-and-conditions/l/long-qt-syndrome.html
Long QT syndrome (LQTS) is a disease that can cause a dangerous rapid heart rate and irregular rhythm involving the bottom pumping chambers of the heart (ventricles). The heart has both muscular and electrical components. Electricity flowing through the heart muscle triggers the muscle to squeeze (contract) or beat.

https://www.hopkinsmedicine.org/health/conditions-and-diseases/long-qt-syndrome-lqts
LQTS is a heart condition that can cause abnormal electrical activity and life-threatening arrhythmias. Learn about the causes, symptoms, diagnosis and treatment of LQTS, and how to prevent triggers and complications.

https://www.nhlbi.nih.gov/health/long-qt-syndrome
Learn about long QT syndrome (LQTS), a rare condition that affects the electrical system of the heart and can cause sudden death. Find out the causes, symptoms, diagnosis, treatment, and prevention of LQTS.

https://www.verywellhealth.com/long-qt-syndrome-8382876
Long QT syndrome is a condition that affects the heart's electrical activity and can cause arrhythmias, fainting, or sudden death. Learn about the types, risk factors, diagnosis, and treatment options for this inherited or acquired disorder.

https://ecgwaves.com/comprehensive-list-of-drugs-causing-qt-prolongation-torsade-de-pointes-and-long-qt-syndrome-lqts/
A comprehensive list of conditions and drugs that may prolong the QT interval, cause torsade de pointes (TdP) and long QT syndrom (LQTS) is presented below. With regards to drugs, the risk of QT prolongation and TdP varies markedly across the list but tends to be rather similar within a drug class.

https://newsnetwork.mayoclinic.org/discussion/mayo-clinic-q-and-a-understanding-and-treating-long-qt-syndrome/
Long QT syndrome is a heart rhythm disorder that can cause fainting, seizures or sudden death. Learn how it's diagnosed, treated and prevented with medications, surgery or a defibrillator.

https://www.ncbi.nlm.nih.gov/books/NBK534864/
The heart has an electrical system that allows it to contract in a rhythm. A vital aspect of this electrical system is depolarization and repolarization. The focus of this activity is on the QT interval. It is measured from the Q wave until the T wave, and the QT interval clinically represents the repolarization of the ventricles. Many commonly used medications exhibit QT-prolonging effects

https://www.pennmedicine.org/for-patients-and-visitors/patient-information/conditions-treated-a-to-z/long-qt-syndrome
Long or prolonged QT interval is the name of the abnormal pattern displayed on an electrocardiogram. Long QT syndrome is often inherited, meaning it runs in the family and you're born with it. It can also develop later in life. Many medications can make the condition worse, including:

https://www.uptodate.com/contents/image?imageKey=CARD/57431
This is not a complete list of all corrected QT interval (QTc)-prolonging drugs and does not include drugs with either a minor degree or isolated association(s) with QTc prolongation that appear to be safe in most patients but may need to be avoided in patients with congenital long QT syndrome, depending upon clinical circumstances.

https://www.ahajournals.org/doi/10.1161/CIRCULATIONAHA.119.039598
In addition, acute QTc increases (ie, ΔQTc >60 ms) are indicative of the exaggerated QTc response that accompanies increased risk of torsades de pointes/SCD in drug-induced LQTS. 3,4 It is interesting to note that even modest QTc prolongation, perhaps mediated by elevated sympathetic tone, subclinical atherosclerosis, and electrolyte/metabolic

https://litfl.com/drugs-causing-qt-prolongation/
October 9, 2020 / 05:08 Reply. I realize your list for QTc prolonging medications is not exhaustive, but I really think it should include ondansetron since its a very commonly used agent. Drugs associated with QT Prolongation, QTc prolongation including Antipsychotics, antiarrhythmics, antidepressants, and antihistamines.