Absence of sympathetic overactivity in Afro-Caribbean hypertensive subjects studied by heart rate variability

Black hypertensives present a greater prevalence of left ventricular hypert rophy and an increased mortality compared to white hypertensives. Differenc es in sympathetic activity might contribute to explain these racial differe nces in hypertension. Nevertheless, previous laboratory studies did not sho w any increase of sympathetic activity direct to the heart in black subject s. The aim of the present study was to investigate the cardiac sympatho-vag al balance in black and white hypertensives analysing heart rate variabilit y, during the entire 24 h. We analysed Holter recordings of 52 essential hy pertensive patients, who had never received antihypertensive treatment, 26 of whom were black and 26 were white. Consecutive series of 300 beats, with 150 beats overlapped (approximately 600 series/day), were considered for t he analysis in time and frequency domain. The mean 24-h value of the power of the low frequency spectral component (0.04-0.15 Hz), expressed in normal ised units, ie a marker of sympathetic modulation, was significantly lower in the group of black patients compared to whites (respectively 40.0+/-2.1 vs 53.6+/-3.6 nu, P< 0.01). Similar results were observed for the LF/HF rat io, an index of the sympatho-vagal balance (respectively 4.11 +/- 0.58 vs 5 .98 +/- 0.79; P< 0.05). In a multiple linear regression analysis, consideri ng diastolic blood pressure, left ventricular mass index, race and age as i ndependent variables, only race (P < 0.002) and age (P < 0.01) could indepe ndently predict the normalised low frequency power or the LF/HF ratio, as d ependent variables. The results of this study suggest some blunting of the cardiac sympathetic neural modulation in black hypertensives compared to wh ite hypertensives, during the entire 24 h.