The relationship between circadian blood pressure pattern and ventricular repolarization dynamics assessed by QT dynamicity

Objective The aim of the present cross-sectional study was to evaluate ventricular repolarization dynamics by QT dynamicity in normotensive and hypertensive individuals with either a non-dipper-type or a dipper-type circadian rhythm of blood pressure (BP). Methods A total of 103 patients were allocated into four groups as follows: (i) normotensive/dipper, n = 28; (ii) normotensive/nondipper, n = 26; (iii) hypertensive/dipper, n = 25; and (iv) hypertensive/nondipper, n = 24. The linear regression slopes of the QT interval measured to the apex and to the end of the T wave plotted against R-R intervals (QTapex/R-R and QTend/R-R slopes, respectively) were calculated from 24-h ambulatory ECG recordings using a dedicated algorithm. Results QTapex/R-R and QTend/R-R slopes were higher in the nondipper subgroup of normotensive cases with respect to the dipper subgroup of normotensive cases (QTapex/R-R=0.171 +/- 0.017 vs. 0.127 +/- 0.023, P = 0.001; QTend/R-R=0.159 +/- 0.015 vs. 0.133 +/- 0.025, P = 0.001). QTapex/R-R and QTend/R-R slopes were higher in the nondipper subgroup of hypertensive cases with respect to the dipper subgroup of hypertensive cases (QTapex/R-R=0.187 +/- 0.019 vs. 0.133 +/- 0.019, P = 0.001; QTend/R-R=0.183 +/- 0.018 vs. 0.147 +/- 0.022, P = 0.001). Pearson's correlation analyses revealed a higher negative correlation between night-time decline in BP and QTapex/R-R (r = -0.638, P = 0.001). There was also a moderate negative correlation between night-time decline in BP and QTend/R-R (r = -0.504, P = 0.001). The correlation coefficients for degree of night-time dipping and QT dynamicity indices were higher in hypertensive groups than in the normotensive groups. Conclusion Blunting of the nocturnal fall in BP associates with impaired QT dynamicity indices in both normotensive and hypertensive groups. Blood Press Monit 17:14-19 (C) 2012 Wolters Kluwer Health vertical bar Lippincott Williams & Wilkins.