Long QT syndrome, or QT prolongation, is a disorder affecting cardiac rhythm. Although generally asymptomatic, it can manifest as palpitations, presyncope, loss of consciousness, seizures, severe hypotension, or even cardiac arrest or sudden death due to torsade de pointes, a serious cardiac rhythm disorder. Long QT syndrome can develop or worsen in certain situations, in particular in very old patients or patients with electrolyte disturbances or various cardiac, hepatic or renal conditions.

Many drugs can prolong the QT interval and provoke torsade de pointes in many therapeutic fields, including antiarrhythmics, neuroleptics, antidepressants, drugs used in attention deficit hyperactivity disorder, antiepileptics, some antibiotics, antiretrovirals, antimalarials, azole antifungals, antihistamines, antiemetics and opioids.

When the decision is taken to use one of these drugs, any risk factors should be corrected if possible before starting the treatment, then monitored. Watch out for interactions with other drugs and grapefruit, which can increase the risk.

QT prolongation often regresses when the dose is reduced, and can generally be reversed by stopping the drug. Tapered discontinuation is sometimes required. If torsade de pointes is observed on an electrocardiogram, the drug should be stopped and the patient monitored by electrocardiography.

Patients with risk factors, including exposure to QT-prolonging drugs, should be informed of the symptoms of cardiac arrhythmias, such as palpitations, dizziness, faintness and syncope.

©Prescrire 1 September 2021

Source: "Drug-induced QT prolongation, torsade de pointes and sudden cardiac death" Prescrire International 2021; 30 (229): 208-214. Subscribers only.

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