Acquired drug-induced long QTc: new insights coming from a retrospective study.

INTRODUCTION: Several drug classes (antiarrhythmics, antimicrobials, antidepressants, phenothiazines, opiates, prokinetics of digestive tract, etc.) have been related to ventricular hyperkinetic arrhythmias such as torsade de pointes (TdP). TdPs are usually heralded by an abnormal prolongation of heart rate-corrected QT interval on the electrocardiogram, so-called drug-induced long heart rate-corrected QT (diLQTc). We do not know to what extent the drug-induced QTc prolongation is able to predict malignant arrhythmias. Thus, we have retrospectively examined the clinical history of patients with diLQTc.

METHODS: The case record, concerning the period January 2008-December 2017, was collected from two hospitals. diLQTc was defined as drug-induced heart rate-corrected QT of ≥ 450 ms or ≥ 470 ms, respectively in male or female patients. The primary purpose was to verify whether in diLQTc patients the length of this electrocardiographic segment was associated with the risk of symptoms or events (TdP, ventricular fibrillation).

RESULTS: Seventy-three validated cases of diLQTc were gathered. Among them, the QTc duration was not able to predict the occurrence of symptoms or events (odds ratio, 0.998; 95% CI, 0.984 to 1.013; p = 0.8821). Likewise, a diQTc lasting longer than 500 ms compared to diQTc comprised between 450 and 500 ms was not associated with an increased risk of arrhythmic events.

CONCLUSIONS: In our diLQTc patients, QTc duration did not predict occurrence of symptoms, or arrhythmic events. Thus, other determinants should be postulated to clarify why sometimes diQTc prolongation propitiates ventricular malignant arrhythmias whereas in other cases this arrhythmogenic effect is lacking.