Usefulness of Low Doses of Atropine to Quantify the Vagal Stimulus-Response Relation in Patients With Congestive Heart Failure

The response of low doses of atropine is reported to be attenuated in patients with congestive heart failure (CHF). Judging from the main site of action of low doses of atropine, we may be able to assess the functional state of the vagal center in the central nervous system. This study examines the clinical significance of heart rate (HR) response to a low dose of atropine in patients with CHF. Low and high doses of atropine were administered intravenously in 72 patients with CHF. HR after a low (parasympathomimetic) dose injection was assessed by the ratio Rm (minimal HR/basal HR), and after a high (parasympatholytic) dose by the ratio R1 (augmented HR/basal HR). Rm and R1 were related to indexes of CHF. Rm increased with progression of CHF (0.92 +/- 0.03 in New York Heart Association functional class I, 0.98 +/- 0.05 in class II, and 1.00 +/- 0.04 in class III). It also correlated with ejection fraction (r = -0.48, p <0.01) and more importantly, with peak oxygen uptake (r = -0.59, p <0.01). R1 exhibited weak correlation with basal HR (r = -0.33, p <0.05) and ejection fraction (r = 0.31, p <0.05), but had no correlation with other indexes. The vagal center may be already blunted in New York Heart Association class II with respect to increased Rm, which may be related to depressed exercise capacity. A low dose of atropine injection offers a simple and safe method for providing important information on the functional state of the vagal center in the central nervous system in patients with CHF.