Acute aldosterone antagonism improves cardiac vagal control in humans

OBJECTIVES We have examined the acute effects (<45 min) of aldsterone antagonism on heart rate variability and baroreflex sensitivity, markers of cardiac vagal control, in 13 healthy subjects. BACKGROUND Evidence for the beneficial effects of aldosterone antagonists comes from studies showing increased survival rates following their addition to standard heart failure therapy. Many mechanisms have been suggested for this action, including effects upon the autonomic nervous system. METHODS Heart rate variability and baroreflex sensitivity were examined 30 min following the administration of potassium canrenoate (intravenous) (aldosterone antagonist) or saline (control). RESULTS Active treatment reduced resting heart rate (-6 +/- 1 beats/min [mean +/- standard error mean]) compared to control (0 +/- 1 beat/min) (p < 0.001) and increased measures of high frequency (HF) heart rate variability. Root mean square of successive RR interval differences increased by 21 +/- 5 ms versus - 6 +/- 5 ms control (p < 0.001); HF power increased by 1,369 +/- 674 ms(2) with aldosterone antagonism compared to -255 +/- 431 ms(2) following saline infusion (p < 0.01). Baroreflex sensitivity (alpha-HF) was increased after active treatment (+4 +/- 2 ms/mm Hg vs. 0 +/- 1 ms/mm Hg control [p < 0.05]). No changes in plasma potassium levels were observed. CONCLUSIONS These results provide evidence that aldosterone antagonists acutely improve cardiac vagal control, irrespective of any diuretic effects, and may in part explain their beneficial effects in treatment of heart failure. (C) 2004 by the American College of Cardiology Foundation.