Congenital Long QT Syndrome: Due to ion channel abnormalities in LQT1 and LQT2 (potassium channels) and LQT3 (sodium channels) that affect cardiac replorization.
Acquired Long QT syndrome: Due to heart disease, electrolyte abnormalities (hypokalemia, hypomagnesemia, hypocalcemia), or exposure to medications that are known to prolong QTc (quinidine, flecainide, sotalol, amiodarone, chloroquines, macrolide and quinoline antibiotics, haldol, citalopram, TCAs, methadone, ondansetron, donepazil, milrinone among others).
Prolonged QTc can lead to syncope, torsades de pointes, and cardiac arrest
Acute management of prolonged QTc:
- Repletion of magnesium to treat torsades de pointes, in addition to potassium and calcium repletion
- Removal of inciting agents
- Avoid antiarrhythmics like amiodarone as this may increase the prolongation
In refractory cases, increasing the underlying heart rate with isoproteronol or transvenous pacing may be required.
Updated definition 2020:
Prolonged QT can be caused by a variety of reasons including medications and electrolyte abnormalities (hypocalcemia, hypomagnesemia, hypokalemia). QT prolongation can also be inherited, the most common syndrome associated with long QT is Romano-Ward syndrome.
Common drugs that cause prolonged QT include:
- Antiarrhythmics – flecainide, procainamide, sotalol, dofetilide, amiodarone
- Psychiatric drugs – haloperidol, droperidol, amitriptyline, nortriptyline, lithium
- Antihistamines – diphenhydramine, loratadine
- Antiemetics – ondansetron
- Antimicrobial and antimalarial – erythromycin, clarithromycin, ketoconazole, chloroquine
- Other agents – methadone, organophosphates, papaverine, vasopressin, adenosine, tacrolimus, cocaine
***this is not a comprehensive list
Prolonged QT can lead to torsades de pointes, a fatal cardiac arrhythmia. Management of prolonged QT syndrome includes avoiding strenuous exercise, monitoring electrolytes, use of beta blockers to control heart rate and insertion of an implantable cardiac device.
References
- Thomas SHL, Behr ER. Pharmacological treatment of acquired QT prolongation and torsades de pointes. Br J Clin Pharmacol. 2016 Mar; 81(3): 420–427. PubMed Link
- Naegle P, Pal S, Brown F, et al. Postoperative QT Interval Prolongation in Patients Undergoing Noncardiac Surgery under General Anesthesia. Anesthesiology 8 2012, Vol.117, 321-328. PubMed Link
- Kies SJ, Pabelick CM, Hurley HA, et al. Anesthesia for Patients with Congenital Long QT Syndrome. Anesthesiology 1 2005, Vol.102, 204-210 PubMed Link
- Yap YG. Drug Induced QT Prolongation and Torsades De Pointes. Heart. 2003; 89(11): 1363–1372 PubMed Link
Other References
- Roden DM. Drug-Induced Prolongation of the QT Interval. NEJM. 2004;350(25): 2618–2621 Link
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