Conditions and symptoms
What Is QT Prolongation? ECG and Medicine Warnings Explained
QT prolongation · say it: Q-T pro-long-GAY-shunAlso written: long QT, prolonged QT interval, QTc prolongation
Short answer
QT prolongation means a part of the heart's electrical cycle, seen on an ECG, takes longer than expected. Some medicines can cause it.
What it means
The QT interval is a measurement on an ECG (heart tracing). It shows how long the heart's lower chambers take to recharge electrically between beats. QT prolongation means this time is longer than expected. On its own it usually causes no symptoms, but a very long QT can raise the chance of a dangerous heart rhythm.
Many medicine labels mention QT prolongation, including some antibiotics, antipsychotics, antidepressants and anti-sickness medicines. The warning is telling your doctor to think about your heart rhythm, your other medicines and your salt levels (such as potassium and magnesium) before and during treatment. Sometimes an ECG is done to check.
QTc is the QT interval corrected for heart rate, and it is the number usually reported. QT prolongation is different from a slow heart rate (bradycardia) or a fast one, though these can be linked.
Where you may see it
- The 'Warnings' section of some antibiotic, antipsychotic and anti-sickness medicine labels
- ECG reports, often written as 'QTc'
- Cardiology letters and drug interaction checks
📄 How it looks on a report
ECG: Sinus rhythm. Prolonged QTc interval.
🙅 What it does not mean
- It does not mean you have had a heart attack.
- A medicine that can prolong QT is not off-limits for everyone. Doctors weigh the risk for each person.
- A borderline result does not by itself mean danger; your doctor will interpret it alongside your other results and medicines.
🎯 Check yourself
Which of these is the right meaning of “QT prolongation”?
🗒️ Questions to ask your doctor
💊 Medicines whose labels mention “QT prolongation”
Plain-English explanations of each medicine, from its official FDA label.
- Artemether and Lumefantrine
an antimalarial medicine, which is a fixed combination of two blood-stage antimalarial ingredients (artemether, an artemisinin derivative, and lumefantrine)
- Azithromycin
a macrolide antibacterial (antibiotic) medicine
- Ciprofloxacin
a fluoroquinolone antibacterial medicine
- Citalopram
a selective serotonin reuptake inhibitor (SSRI), a type of antidepressant medicine
- Famotidine
A histamine-2 (H2) receptor blocker, a type of medicine that lowers stomach acid.
- Fluconazole
an azole antifungal medicine, a type of medicine that treats fungal (yeast) infections
- Fluoxetine
a selective serotonin reuptake inhibitor (SSRI), a type of antidepressant medicine
- Hydroxychloroquine
an antimalarial and antirheumatic drug, which means it is used for malaria and for certain joint and immune conditions
- Loperamide
a synthetic antidiarrheal medicine
- Metronidazole
An antimicrobial medicine of the nitroimidazole type, used to treat certain bacterial and parasitic infections
🔗 Read more from trusted sources
- “QT prolongation” on MedlinePlus ↗
US National Library of Medicine
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