Background QTc (corrected QT interval) prolongation can lead to acute ventricular arrhythmias. A risk factor for this condition is the use of drugs that potentially prolong the QTc interval.

Purpose To analyse the effect of QTc-prolonging drugs (QTPDs) on the QTc interval of patients admitted to cardiology units. Drug-drug interactions that could increase this effect were also evaluated.

Material and methods Observational, prospective study was completed in a tertiary hospital (1,350 beds) from July–September 2014. QTc intervals upon admission were measured by two arrhythmologists for prolonged QTcs (>450 ms for men, >460 ms for women per American Heart Association/European Heart Association consensus). Patients with pacemakers or wide QRS (>120 ms) were excluded. Home and inpatient drug treatment regimens were evaluated by pharmacists for QTPDs and drug-drug interactions.

Results Over the study period, 111 patients were evaluated (median age = 71.8 years, 38.2% female). Upon admission, 34 patients (30.6%, 95% CI: 22.2–40.1) had a prolonged QTc interval (mean QTc = 488.53 ± 21.8 ms). Of these, 9 patients (26.5%) had a home regimen that included at least one QTPD. A difference was not found between the mean QTcs of patients treated with QTPDs (486.0 ± 17.8 ms), QTPDs with interacting drugs (487.8 ± 20.8 ms), or no QTPDs (480.5 ± 22.1 ms). Half of the QTPDs prescribed were antidepressants. Furthermore, 18 patients (52.9%) were taking interacting medicines prior to admission that potentially contributed to this QTc prolongation (beta-blockers = 94.0%; diuretics = 61.1%).

Conclusion Almost one-third of patients hospitalised in cardiology units had a prolonged QTc interval at admission, increasing their risk of developing potentially fatal arrhythmias. Before hospitalisation, the majority of patients were receiving QTPDs or interacting medicines; however, this study did not observe a related increased risk of QTc prolongation (limited by a small sample size). It is unknown how further treatment in the hospital affects these patients’ risk. Therefore, it is recommended to evaluate QTc intervals of cardiology patients upon admission and closely monitor for additional risk factors of QTc prolongation and arrhythmias during hospitalisation.

References and/or acknowledgements Nursing staff

No conflict of interest.