Exaggerated QT prolongation after cardioversion of atrial fibrillation

J Am Coll Cardiol. 1999 Aug;34(2):396-401. doi: 10.1016/s0735-1097(99)00226-0.


Objectives: The purpose of this study was to test the hypothesis that the extent of drug-induced QT prolongation by dofetilide is greater in sinus rhythm (SR) after cardioversion compared with during atrial fibrillation (AF).

Background: Anecdotes suggest that when action potential-prolonging antiarrhythmic drugs are used for AF, excessive QT prolongation and torsades de pointes (TdP) often occur shortly after sinus rhythm is restored.

Methods: QT was measured in nine patients with AF who received two identical infusions of dofetilide: 1) before elective direct current cardioversion and 2) within 24 h of restoration of SR.

Results: During AF, dofetilide did not prolong QT (baseline: 368 +/- 48 ms vs. drug: 391 +/- 60, p = NS) whereas during SR, QT was prolonged from 405 +/- 55 to 470 +/- 67 ms (p < 0.01). In four patients (group I), the SR dofetilide infusion was terminated early because QT prolonged to >500 ms, and one patient developed asymptomatic nonsustained TdP. The remaining five patients (group II) received the entire dose during SR. Although deltaQT was greater in group I during SR (91 +/- 22 vs. 45 +/- 25 ms, p < 0.05), plasma dofetilide concentrations during SR were similar in the two groups (2.72 +/- 0.96 vs. 2.77 +/- 0.25 ng/ml), and in AF (2.76 +/- 1.22 ng/ml). DeltaQT in SR correlated inversely with baseline SR heart rate (r = -0.69, p < 0.05), and QT dispersion developing during the infusion (r = 0.79, p < 0.01).

Conclusions: Shortly after restoration of SR, there was increased sensitivity to QT prolongation by this I(Kr)-specific blocker. Slower heart rates after cardioversion and QT dispersion during treatment appear to be important predictors of this response.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Anti-Arrhythmia Agents / therapeutic use
  • Atrial Fibrillation / physiopathology
  • Atrial Fibrillation / therapy*
  • Atrial Flutter / physiopathology
  • Atrial Flutter / therapy
  • Electric Countershock*
  • Electrocardiography* / drug effects
  • Female
  • Heart Rate / drug effects
  • Humans
  • Male
  • Phenethylamines / therapeutic use
  • Sulfonamides / therapeutic use


  • Anti-Arrhythmia Agents
  • Phenethylamines
  • Sulfonamides
  • dofetilide