• ventricular repolarization;
  • monophasic action potential;
  • ibutilide;
  • QT interval;
  • torsades de pointes

Introduction: Ibutilide has been shown to prolong repolarization times and increase the risk of ventricular tachyarrhythmias particularly in patients with structural heart disease. The mechanisms underlying its proarrhythmic effects remain incompletely understood. We sought to define the effects of ibutilide on the temporal lability of ventricular repolarization in patients with and without structural heart disease.

Methods: Twenty-four patients referred for electrophysiology study underwent monophasic action potential (MAP) recordings in the right ventricle during sinus rhythm and random interval right atrial pacing (RIAP). Ibutilide was subsequently administered and the recordings repeated both in sinus rhythm and with RIAP. Digitized recordings were analyzed offline for calculation of the QT variability index (QTVI) based on surface ECG, and the MAP duration variability index (MAPDVI) based on the intracardiac MAP signal.

Results: Of 24 patients enrolled, analyses were performed in 21 patients (mean age 59 ± 15 years, 38% women). In three patients, the data were not analyzed due to frequent premature ventricular complexes. Ibutilide resulted in significant changes in heart rate (mean difference: −7.4 ± 0.91 bpm, P < 0.0001) and the surface QT interval (mean difference: 59.6 ± 12.2 ms, P = 0.0001) during sinus rhythm. After ibutilide, QTVI remained unchanged from baseline during sinus rhythm but was significantly different in the setting of RIAP (mean difference: 0.345 ± 0.098, P = 0.0022). With subgroup analyses, these differences remained significant regardless of the presence or absence of heart disease.

Conclusion: Ibutilide results in overall prolongation of ventricular repolarization and reductions in baseline sinus rates. Ibutilide increases temporal lability of repolarization only with enriched fluctuations in heart rate.