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Keywords:

  • QT interval;
  • torsades de pointes;
  • arrhythmia;
  • epidemiology

Abstract

Background:  QT interval prolongation carries an increased risk of torsade de pointes and death.

Aim:  We sought to determine the prevalence of QT prolongation in medical inpatients and to identify determinants of this condition.

Methods:  We enrolled consecutive patients who were admitted to the internal medicine ward and who had an electrocardiogram performed within 24 h of admission. We collected information on baseline patient characteristics and the use of QT-prolonging drugs. Two blinded readers manually measured the QT intervals. QT intervals were corrected for heart rate using the traditional Bazett formula and the linear regression-based Framingham formula. We used logistic regression to identify patient characteristics and drugs that were independently associated with QTc prolongation.

Results:  Of 537 inpatients, 22.3% had a prolonged QTc based on the Bazett formula. The adjusted odds for QTc prolongation based on the Bazett correction were significantly higher in patients who had liver disease (OR 2.9, 95% CI: 1.5–5.6), hypokalaemia (OR 3.3, 95% CI: 1.9–5.6) and who were taking ≥1 QT-prolonging drug at admission (OR 1.7, 95% CI: 1.1–2.6). Overall, 50.8% of patients with QTc prolongation received additional QT-prolonging drugs during hospitalisation.

Conclusions:  The prevalence of QTc prolongation was high among medical inpatients but depended on the method used to correct for heart rate. The use of QT-prolonging drugs, hypokalaemia and liver disease increased the risk of QTc prolongation. Many patients with QTc prolongation received additional QT-prolonging drugs during hospitalisation, further increasing the risk of torsade de pointes and death.