EFFECT OF LONG-TERM DIGOXIN THERAPY ON AUTONOMIC FUNCTION IN PATIENTSWITH CHRONIC HEART-FAILURE

Objectives. This study was conducted to determine the effect of long-t erm digoxin therapy on autonomic function in patients with mild to mod erate chronic heart failure. Background. Chronic heart failure is char acterized by increased sympathetic activity and decreased parasympathe tic activity. Intravenous digitalis has been found to reduce sympathet ic activity immediately in these patients, but whether short-term neur ohormonal effects are sustained during long-term oral therapy has not been assessed. Methods. We determined sympathetic activity in 26 patie nts with heart failure by measuring plasma norepinephrine levels and p arasympathetic activity from variables of heart period variability der ived from 24-h ambulatory electrocardiographic Holter recordings obtai ned before and after 4 to 8 weeks of digoxin therapy. Results. After d igoxin therapy, plasma norepinephrine decreased significantly from a m ean +/- SEM of 552 +/- 80 to 390 +/- 37 ng/ml. In addition, the RR int erval increased significantly from 719 +/- 19 to 771 +/- 20 ms. High f requency power increased from 84 +/- 24 to 212 +/- 72 ms(2), and the r oot mean square of successive differences in RR interval increased fro m 20.3 +/- 1.8 to 27.0 +/- 3.4 ms, indicating a substantial increase i n parasympathetic activity. Low frequency power, an index of barorefle x activity, was also significantly increased (239 +/- 80 to 483 +/- 14 4 ms(2)) by digoxin therapy. Conclusions. These results indicate 1) th at long-term therapy with digoxin acts to ameliorate the autonomic dys function of patients with heart failure, and 2) that the short-term ne urohormonal effects of digoxin are sustained during prolonged treatmen t with the drug.