Does sympathetic overactivation feature all hypertensives? Differences of sympathovagal balance according to night/day blood pressure ratio in patients with essential hypertension

When evaluating the 'night/day BP ratio', both hypertensives and normotensives can be arbitrarily classified into four groups: extreme dippers (ratio ≤0.8), dippers (0.8<ratio ≤0.9), mild dippers (0.9<ratio≤1.0) and reverse dippers (ratio ≥1.0). Reverse and mild dipper hypertensives have poorer prognoses compared with the physiological dipper profile, but the prognostic relevance of the extreme dipper profile remains uncertain. The evaluation of heart rate variability (HRV), obtained by 24-h Holter ECG monitoring, is the most frequently used noninvasive form of assessment of the activity of the autonomic nervous system. Reverse and mild dipper hypertensives have reduced HRV, indicating an overactivation of the sympathetic nervous system (SNS); however, the HRV behavior in extreme dippers is still controversial. The goal of this study was to compare HRV indexes of extreme vs. reverse dipper essential hypertensives measured on the basis of time domains. We enrolled 125 hypertensive subjects, divided in 4 quartiles according to day/night blood pressure (BP) ratios. The upper and lower quartiles (31 subjects per quartile) were compared; 30 normotensive subjects were enrolled as a control group. Time domain HRV parameters of the three groups revealed a higher degree of sympathetic activation in the lower quartile (reverse dipper) vs. the upper quartile (extreme) and normotensive controls. HRV parameters related to parasympathetic tone did not show any significant variations among the three groups. Contrary to common belief, not all hypertensives have SNS overactivation.