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.