Epidemiologic study findings reveal that alterations in cardiac autonomic function (CAF) are already present in normotensive individuals with a family history of hypertension (FHH) and those with prehypertension.

Chih-Jen Chang (National Cheng Kung University Hospital, Taiwan, Republic of China) and colleagues measured cardiac autonomic function (CAF) in 1436 individuals in Tainan City, Taiwan, comparing changes in CAF across the different blood pressure (BP) groups: normotensive with no FHH (NT[-]); normotensive with FHH (N[+]); prehypertension (BP 120-139/80-89 mmHg); and hypertension (BP ≥140/90 mmHg).

They determined CAF by the standard deviation of normal-to-normal intervals or RR-intervals (SDNN), power spectrum in low frequencies (LF) and high frequencies (HF) and the LF/HF ratio in supine position for 5 min, the ratio between the longest RR-interval at approximately the 30th beat and the shortest RR-interval at approximately the 15th beat after standing (30 max/15 min ratio), and the ratio between the longest RR-interval during expiration and the shortest RR-interval during inspiration (E/I ratio).

All measured CAF indexes differed significantly among the various BP groups, the team reports in the Journal of the American College of Cardiology.

• NT(+)
• prehypertensive
• and hypertensive individuals
• had lower parasympathetic drive,
• as indicated by the E/I ratio
• the 30 max/15 min ratio
• and HF power after adjustment for covariates,
• than NT(-) individuals.

However, SDNN did not differ among NT(-), NT(+), pre-hypertensive, and hypertensive individuals.

Prehypertensive individuals had higher LF power than that of NT(-) participants, but neither NT(+) nor hypertensive individuals exhibited higher LF power than that of NT(-) participants after adjustment for other variables.

In the sympathovagal balance domain, both prehypertensive and hypertensive patients displayed higher square roots of LF/HF ratios than those of NT(-) participants, but there was no difference in the square roots of LF/HF ratios between NT(+) and NT(-) individuals after adjustment for other confounders.

In a related editorial, Daniel Duprez (University of Minnesota, Minneapolis, USA) commented:

•  "The future challenge is to investigate whether nonmedical and medical regimens can restore the equilibrium of the cardiac autonomic balance in normotensive subjects with a positive family history of hypertension and in subjects with prehypertension in order to prevent or delay the development of hypertension and its cardiovascular damage."

J Am Coll Cardiol 2008; 51: 1896-1901