Ibutilide-induced alterations in electrocardiographic and spatial vectorcardiographic descriptors of ventricular repolarization.

BACKGROUND

Ibutilide is used for the pharmacologic cardioversion of atrial fibrillation (AF) or flutter (AFl). Ibutilide-induced QT interval prolongation has been demonstrated previously. However, its effects on vectorcardiographic (VCG) descriptors of ventricular repolarization (VR) have not been studied so far.

HYPOTHESIS

To evaluate the effects of ibutilide on electrocardiographic (ECG) and VCG descriptors of VR, one or two repeated 10-min infusions of 1 mg of ibutilide were given in 50 consecutively recruited patients (36 women, mean age 69.4 +/- 9.3 years) with AF or AFl of recent onset.

METHODS

The maximum and the minimum QT intervals, QT dispersion, the rate-corrected QT maximum, and the spatial VCG descriptors, spatial T amplitude, and spatial QRS-T angle were calculated before (baseline ECG) and 30 min after the start of ibutilide infusion (postinfusion ECG).

RESULTS

After ibutilide infusion, 40 (80%) patients were cardioverted to sinus rhythm (Group 1), while in the remaining 10 (Group 2) AF or AFl persisted. In both study groups, temporal measures of VR were significantly increased from baseline to the postinfusion ECG. In Group 1, spatial T amplitude and spatial QRS-T angle did not differ between those two ECGs, while in Group 2 spatial T amplitude was significantly increased (p = 0.005) and spatial QRS-T angle was significantly decreased (p = 0.002) post infusion compared with baseline ECG.

CONCLUSIONS

While temporal measures of VR are significantly affected in all patients who receive ibutilide infusion for AF or AFl cardioversion, spatial VCG descriptors of VR are significantly altered only in those patients who fail to respond to the drug. A dose-related effect of ibutilide on the different aspects of VR should be suspected.