CONGESTIVE-HEART-FAILURE AND VVI PACING MODE - DYNAMIC BEHAVIOR OF THE DISPERSION OF VENTRICULAR REPOLARIZATION

Dynamic Behavior of the Dispersion of Ventricular Repolarization. The aim of this study was to evaluate the circadian variation in the spati al dispersion of ventricular repolarization in continuously paced pati ents with congestive heart failure (CHF). Fourteen patients (10 males, 4 females, aged 65 +/- 8 years) with CHF due to dilated cardiomyopath y (DCM) and an echocardiographic ejection fraction of 28% +/- 3% were studied. All patients underwent AV junctional RF ablation and permanen t pacemaker implantation for drug refractory chronic atrial fibrillati on (AF). Patients were evaluated at 1 month postimplant with a three-c hannel 24-hour Holter monitor, using the three plane Frank orthogonal leads (X, Y, and Z), in VVI pacing mode at 70 beats/min. For each hour , the mean value of spike-T interval dispersion of the first five beat s was measured. The control group consisted of 20 patients without str uctural heart disease, but with AF and complete Ali block, continuousl y paced in VVI mode at 70 beats/min. The dispersion of the spike-T int erval had a circadian behavior in the study population, with higher va lues at night and lower during the daytime. During the daytime, the me an value of spike-T interval dispersion was 39 +/- 5 ms and during the nighttime it was 45 +/- 7 ms (P = 0.003). Such a difference between d ay and night was not found in the control group (38 +/- 6 ms and 40 +/ - 8 ms, respectively, P = NS). In the daytime period the mean value of spike-T interval dispersion of our study population was comparable to that of the control group (P = NS), while during the nighttime if was significantly higher (P = 0.0004). In conclusion, by evaluating the d ispersion of ventricular repolarization in two dimensions, space and t ime, a circadian variation was found in paced patients with CHF due to DCM. The increased QT dispersion in these patients during the nightti me period was attributed to different effects of vagal activity in nor mal and abnormal myocardial areas.