Prolonged QT Interval: Causes, Consequences-and Prevention

When the QT interval is prolonged, amultifocal ventricular tachycardiasyndrome (torsades de pointes) mayoccur and produce sudden cardiacdeath. QT prolongation can resultfrom congenital abnormalities, suchas the long QT interval syndrome, orfrom certain drugs. Other factors thatincrease the risk of a prolonged QTinterval and torsades de pointes includehypokalemia, hypomagnesemia,older age, female sex, low ventricularejection fraction, ischemia,and low heart rate.Numerous drugs have been implicatedin QT interval prolongation,including antiarrhythmics, antipsychotics,and antidepressants (Table).Before you prescribe a drug that canprolong the QT interval, make sureits benefits outweigh the potential forharm. This is especially importantwhen multiple agents are indicated. Ifa drug that can prolong the QT intervalis prescribed (particularly an antiarrhythmic),obtain an initial ECGand repeat the study if other drugsare added to the regimen.Certain antibiotics, includingquinolones, may prolong the QT interval.Although the overall risk is notstatistically great, be aware of the potentialrisk. You may decide that an alternativeantibiotic would be moreprudent or that an ECG is warranted.The FDA is working on guidelinesto assess QT interval prolongationduring clinical trials. When thefinal version is available, clinicianswill have a more reliable road map formaking safe medication choices.Meanwhile, there is no substitute forconsidered clinical judgment.

References:

REFERENCE:

1.

Al-Khatib SM, LaPointe NMA, Kramer JM, CaliffRM. What clinicians should know about the QT interval.

JAMA.

2003;289:2120-2127.