In reply: We agree that there are no guidelines defining torsade de pointes based on intracardiac electrograms, but there are several reasons why the likelihood of torsade de pointes (as opposed to any other arrhythmia) in our patient is high.

The electrogram shows the arrhythmia just before delivery of direct current shock, this being about 30 minutes after the patient took her first ever dose of loratadine. There are marked variations in electrogram morphology, despite minimal variation in RR interval, in a short strip of recording in this patient with documented QT prolongation. Further, she had no history of monomorphic ventricular tachycardia, no inducible monomorphic ventricular tachycardia at electrophysiologic examination, and no evidence of structural heart disease. Neither was a mechanism for supraventricular arrhythmia identified.

The absence of initiating beats showing pause-dependence is unfortunate, but this is not provided by the generation of device implanted in this patient. Hence, we believe the word "probable" is an apt description for the observation made.