Acquired long QT interval: a case series of multifactorial QT prolongation

Abstract

Background: Acquired long QT (LQT) interval is thought to be a consequence of drug therapy and electrolyte disturbances.

Hypothesis: We characterize the potential effects of polypharmacy in a case series of acquired LQT and torsades de pointes (TdP) in order to determine whether multiple risk factors play a role in the development of LQT.

Methods: The case series consisted of 11 patients presenting to 4 tertiary care hospitals with LQT and ≥ 2 risk factors for developing LQT. Clinical characteristics, medications, electrolyte disturbances, and course in hospital were analyzed.

Results: Mean age was 49.1 ± 5.8 years. Eight patients were female. Four had hypertension, 1 had a history of dilated cardiomyopathy, and 1 patient demonstrated complete atrioventricular block. Average QTc interval at presentation was 633.8 ± 29.2 ms. Nine patients developed TdP. In 3, LQT was not initially detected and amiodarone was administered, followed by development of TdP. Patients were taking an average of 2.8 ± 0.3 QT-prolonging medications-an antidepressant in 6 cases and a diuretic in 8 cases. All patients had an electrolyte abnormality; 8 patients presented with severe hypokalemia (<3.0 mmol/L). Average serum potassium and magnesium were 2.82 ± 0.10 mmol/L and 0.75 ± 0.03 mmol/L, respectively. There were no deaths.

Conclusions: This case series highlights the risks of polypharmacy in the development of LQT and TdP. It illustrates the importance of early detection of LQT in patients with multiple risk factors in ensuring appropriate treatment.

Figure 1

Sample electrocardiogram (A) of patient 3 at admission; QTc = 549 ms. Sample electrocardiogram (B) demonstrating TdP as obtained by telemetry monitor. Abbreviations: QTc, corrected QT interval; TdP, torsades de pointes.