Classification of LQTS Cases*
*According to Confidence in Drug-Induced Long QT Syndrome Diagnosis and the Presence of Cofactors
Drug-induced Long QT syndrome (LQTS):
Prolonged QT intervals (QTc>460 msec) plus polymorphic ventricular arrhythmia fitting the description of torsades de pointes temporally associated with the administration of a drug or combination of drugs.
Drug-induced LQTS Cofactors:Agents or conditions known to induce or facilitate the induction of LQTS (e.g., agents that directly prolong the QT interval, including drugs that inhibit the metabolism of drugs known to prolong the QT interval), and conditions such as hypokalemia, hypomagnesemia and bradycardia that might enhance the action of an agent that induces LQTS.
Classification of Episodes When Temporally Associated with Drug Administration
High confidence in Drug-induced LQTS diagnosis:
Electrocardiographic documentation of long QT and torsades de pointes
Sudden death, ventricular tachycardia, or torsades de pointes with measurements, statement, or electrocardiograms, indicating prolonged QT intervals.
Syncope with polymorphic premature ventricular contractions (PVCs) and measurements, statements or electrocardiograms indicating prolonged QT intervals with resolution of arrhythmia and QT intervals when LQTS factors are removed.
Medium confidence in Drug-induced LQTS diagnosis:
Sudden death, ventricular fibrillation, ventricular tachycardia, or syncope with no plausible cause and without documented long QT interval (unspecified, normal when measured only from monitor strips, or otherwise equivocal).
Ventricular tachycardia or ventricular fibrillation without documented prolonged QT interval, which subsides after removal of LQTS factors.
Syncope without documented ventricular tachycardia but with documented prolonged QT interval.
Low confidence in Drug-induced LQTS diagnosis:
Sudden death, ventricular fibrillation, ventricular tachycardia or syncope with plausible cause and normal QT interval.
Syncope without documented ventricular tachycardia with a normal QT interval.
Isolated QT prolongation:
Prolonged QT interval without associated arrhythmia or clinical events.
Not Drug-induced LQTS:
Another condition (e.g., acute myocardial infarction, aspiration, bradyarrhythmia) or artifact identified as the basis for the ventricular tachycardia, ventricular fibrillation, sudden death, or syncope; no prolonged QT interval documented or stated.
This classification is adapted with permission from the work of Drs. Ralph Lazarra, Doug Zipes and Jean Barbey.