QRS Dispersion Index During Tilt Test in Patients with Transient Loss of Consciousness

Objectives: The QRS dispersion index (QRSd) is the difference between the minimum and maximum duration of the QRS complex. QRSd is reported to have prognostic values and is associated with arrhythmias and mortality. There is a lack of information regarding QRSd changes during the tilt test (TT). This study was conducted to determine the QRSd changes during TT in patients with transient loss of consciousness. Methods: This descriptive-analytical study was conducted retrospectively. The QRSd was compared in the three stages of the TT: rest (baseline), tilt, and recovery. Repeated measure ANOVA was used for normally distributed variables; otherwise, Friedman's nonparametric test was used, and Bonferroni's adjusted test was used for pairwise comparisons in subgroups. Results: The mean and standard deviation of QRS complex duration in milliseconds (QRSt) in baseline, tilt, and recovery were 0.105±0.011, 0.099±0.015, and 0.103±0.013 in negative TT and 0.106±0.015, 0.099±0.017, and 0.170±0.103 in positive TT, respectively. There was a significant difference between baseline and tilt in the negative group and between baseline and tilt, and tilt and recovery in the positive group (P<0.05). The mean and standard deviation of QRSd in both groups between baseline, tilt and recovery were 0.035±0.009, 0.033±0.01 and 0.027±0.01 in negative TT and 0.039±0.013, 0.039±0.013 and 0.025±0.009 in positive TT, respectively. A significant difference was found between baseline and recovery in the negative group (P=0.048) and between baseline and recovery, and tilt and recovery in the positive group. (P<0.05). In women with positive TT, the QRSt was significantly different between baseline and tilt (P=0.005). This difference was not observed in men with positive TT. In the positive TT group, the comparison of QRSt and QRSd in sex and age subcategories had significant differences. This finding was not observed in the negative TT group. Conclusions: Patients with positive and negative TT have different QRSd changes. TT-induced QRSd changes may be sex and age- dependent. Hemodynamic-autonomic reflexes during TT are associated with increased inhomogeneity of conduction velocity during ventricular depolarization.