EFFECT OF CLONIDINE ON HEART-RATE-VARIABILITY IN CONGESTIVE-HEART-FAILURE

In patients with congestive heart failure, abnormal heart rate variabi lity is a predictor of total mortality and sudden cardiac death. Drugs that improve heart rate variability may have a potential role for imp roving the survival among these patients. The effects of clonidine wer e studied in 24 patients with congestive heart failure, sinus rhythm, a left ventricular ejection fraction <0.40, and systolic blood pressur e >115 mm Hg. A 6-minute corridor walk test and 24-hour Holter monitor ing were performed before and 42 +/- 24 days after initiation of cloni dine therapy (Catapres-TTS patch, mean dose: 0.33 +/- 0.21 mg). Change s in other medications used at baseline were not allowed. One patient died suddenly. Two patients did not complete the protocol due to worse ning congestive heart failure, which required changes in medications, 1 patient discontinued due to hypotension, and 2 for personal reasons. Among the 18 patients who completed the protocol, the mean RR interva l of sinus beats increased from 760 +/- 106 to 822 +/- 125 ms (p = 0.0 01) and the distance covered during the 6-minute walk test increased f rom 1,148 +/- 277 to 1,255 +/- 359 feet (p = 0.042). Systolic blood pr essure decreased from 139 +/- 15 to 119 +/- 10 mm Hg (p <0.0001). The following increases were noted in the heart rate variability measureme nts: high-frequency power in 0.15 to 0.40 Hz: 4.58 +/- 1.07 to 4.94 +/ - 1.17 In (ms), p = 0.002; SD: 47.0 +/- 16.9 to 52.5 +/- 18.4 ms, p = 0.034; SD of the mean of all RR intervals in 24 hours: 116 +/- 94 to 1 30 +/- 19 ms, p = 0.033; SD of all 5-minute mean RR intervals: 106 +/- 44 to 124 +/- 66 ms, p = 0.042; root-mean square of difference of suc cessive RR intervals: 28.8 +/- 10.7 to 34.1 +/- 14.2 ms, p = 0.017. Cl onidine improves heart rate variability in the patients with congestiv e heart failure by increasing the parasympathetic tone. It is well tol erated by most patients with heart failure and may have a beneficial e ffect on exercise capacity. (C)1998 by Excerpta Medica, inc.