Drug use and torsades de pointes cardiac arrhythmias in Sweden: a nationwide register-based cohort study

OBJECTIVE: To study the occurrence of torsades de pointes (TdP) ventricular tachycardia in relation to use of drugs labelled with TdP risk, using two nationwide Swedish registers. DESIGN: Prospective register-based cohort study. SETTING: Entire Sweden. PARTICIPANTS: Persons aged ≥18 years prescribed and dispensed any drug classified with TdP risk during 2006–2017, according to CredibleMeds. Persons with a registered TdP diagnosis during the study period, using drugs labelled with known (TdP 1), possible (TdP 2) or conditional (TdP 3) risk at the incident of TdP were examined. PRIMARY OUTCOME MEASURES: Occurrence of TdP in relation to exposure rates for individual drugs with TdP risk. SECONDARY OUTCOME MEASURES: Concurrent use of more than one TdP-labelled drug in a person with a TdP diagnosis. RESULTS: During the study period, 410 TdP cases using drugs with TdP risk labels at the incident were registered; 205 women and 205 men, mean age 74.0 and 71.5 years, respectively. Antidepressants dominated (129/410, 30%), followed by antiarrhythmics (17%). Diuretics and gastric acid-secretion inhibitors, with TdP risk related to induction of hypokalaemia or hypomagnesaemia, were used in 56% and 32% of the 410 TdP cases, respectively. Among the most used antidepressants, citalopram with known TdP 1 risk was associated with both a higher absolute number and incidence of TdP per 100 000 users (two to four times), compared with mirtazapine with possible (TdP 2), and sertraline with conditional (TdP 3) risk. Multiple risk factors, including advanced age, cardiovascular disease and treatment with more than one TdP-classified drug, were frequently observed. CONCLUSIONS: Antidepressants followed by antiarrhythmics dominated among TdP risk drugs used by adults with TdP diagnosis, the majority being ≥65 years. TdP risk class and concomitant medication should be considered when prescribing antidepressants to older patients.