Ventricular tachycardia following ingestion of a commonly used antihistamine

To the Editor: Kuchar et al1 describe a patient who received an implantable defibrillator discharge after a single ingestion of loratadine. We are concerned that their conclusion — that this patient "probably" had drug-induced torsade de pointes — is incorrect.

Review of the intracardiac electrograms from this patient (shown in Box 2 of their article) with known monomorphic ventricular tachycardia (VT; shown in their Box 1) shows a relatively fixed rate of the VT without the large variations in cycle length consistent with torsade de pointes.

While there are no established guidelines for determining torsade de pointes based on intracardiac electrograms, it is clear that during monomorphic VT electrocardiograms can show variability in amplitude and orientation. Consistent with the early stages of monomorphic VT,2 the first three electrograms have a different orientation compared with the remaining electrograms, which are largely similar. Unfortunately, as the transition from supraventricular rhythm to tachycardia was not shown, it cannot be ascertained whether the tachycardia began with a pause-dependent mechanism, an important criterion to help diagnose torsade de pointes.3 Given that this patient's implantable defibrillator intracardiac electrograms do not show a continually changing electrogram pattern, that the cycle length is relatively constant, and that there is a lack of documented QT prolongation, there is no evidence of the patient's arrhythmia being torsade de pointes.

Incidentally, it is unclear whether these electrograms were recorded before (as specified in the discussion) or after defibrillator discharge (title of Box 2). It is well documented that a defibrillator discharge can have significant effects on the recording of intraventricular electrograms. Most likely, this patient, with documented pre-existing monomorphic VT (their Box 1[b]), had an episode of VT (not torsade de pointes) appropriately treated by the implanted defibrillator, probably having no direct relationship with loratadine. Notably, their Box 3 shows torsade de pointes in another patient, not receiving loratadine.

In summary, Kuchar et al1 correctly state that there have been no documented episodes of torsade de pointes after ingestion of loratadine. Similarly, their report does not appear to document an episode of torsade de pointes.