QT prolongation means the heart takes too long to recover electrically after each beat, seen as a long QTc on the ECG. It can be inherited or caused by drugs and low electrolytes, and it raises the risk of torsades de pointes and sudden death.
Key symptoms
- Often no symptoms
- Palpitations
- Fainting, in inherited forms often triggered by exercise, a sudden noise or sleep
- Seizure-like episodes from brief arrhythmias
What you find on exam
- Usually a normal exam
- Medication review: antiarrhythmics, macrolides, fluoroquinolones, antipsychotics, ondansetron, methadone
- Signs of an eating disorder, vomiting or diarrhea
- Family history of sudden death or congenital deafness
Tests
- 12-lead ECG: QTc above about 450 ms in men or 460 ms in women; 500 ms or more is high risk
- Potassium, magnesium and calcium
- Repeat ECG after starting or changing a QT-prolonging drug
- Genetic testing and family screening if inherited
Treatment basics
- Stop QT-prolonging drugs
- Keep potassium at 4 mEq/L or more and magnesium at 2 mg/dL or more
- Torsades: IV magnesium sulfate 2 g; defibrillate if unstable
- Inherited long QT: beta blocker such as nadolol; defibrillator if high risk
Red flags
- QTc of 500 ms or more
- Fainting, or torsades on the monitor
- Several QT-prolonging drugs with low potassium or magnesium
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Sources: NCCPA PANCE Content Blueprint; NBOME COMLEX-USA clinical presentations; AAMC Core Entrustable Professional Activities (Core EPAs). Written by Making Synapses. Making Synapses is not affiliated with these organizations.