[Dynamic of the changes of the paced QT dispersion after ventricular pacemaker implantation (WIR) and radiofrequency atrioventricular junction ablation in drug refractory atrial fibrillation].

INTRODUCTION: Transcutaneous RF catheter ablation of the atrioventricular junction (AVJ) in pts with ventricular pacemaker (VVIR) implantated is an accepted treatment for drug-intolerant or drug refractory atrial fibrillation. The ventricular arrhythmias and sudden cardiac death may be associated with increased of QT dispersion (QTD), mainly in pts with reduced LV function (low ejection fraction - EF) after AVJ ablation. The present study evaluates the dynamic of the changes of QTD in response to a sudden pacing rate drop from 80/min to 40/min in follow up 1 day, 3, 6 and 9 months after ablation (1d, 3m, 6m, 9m).

MATERIAL AND METHODS: The 12-lead ECGs were recorded on 22 pts (mean age 72.6+/-5.4 yrs) (10 with low EF (<50%) - group A, 12 with normal EF (> or =50%) - group B) on the 1 day, 3, 6 and 9 months following AVJ ablation during a sudden drop in ventricular pacing rate from 80 to 40 beats/min. The maximum QT interval (QTM), minimum QT interval (QTm), and QTD were measured on the last 5 beats prior to the rate drop (QTM-80, QTm-80, QTD-80) and on the first 5 beats after the rate drop (QTM-40, QTm-40, QTD-40). These QT parameters were compared. The echocardiographical studies were performed on the 1d, 3m, 6m and 9m following AVJ ablation.

RESULTS: In response to a sudden paced heart rates drop from 80 to 40 beats/min, the DeltaQTM (QTM-40 - QTM-80) increased during follow-up in both groups, while the DeltaQTm (QTm-40-QTm-80) increased in group B(23.3+/-25.7 in 1d, 27,5+/-20.1ms in 9m; p< 0.001), but not in group A (1+/-16.6 in 1d, 5+/-25.1ms in 9m). Consequently, the AQTD (QTD-40 - QTD-80) increased significantly in group A at 6 months (29+/-31.1ms; p<0.05) but not in group B (9.2+/-17.3msl. The negative correlation between QTD-40, QTD-80 and EF was observed in group A.

CONCLUSIONS: Following AVJ ablation, QTD increased during a sudden rate drop in pts with reduced LV function, but not in pts with EF > or = 50%. The significant correlation between QTD and paced rate was found in pts with LV dysfunction. The increased QTD in response to a sudden heart rate drop in pts with low EF was due to a failure of the expected prolongation of the QTm.