Effect of adenosine on heart rate variability in humans

By stimulating afferent nerve endings in skeletal muscle, heart, kidney and the carotid body, adenosine infusion evokes a receptor-specific sympatho-e xcitatory reflex in humans that overrides its direct negative chronotropic effect. We tested the hypothesis that adenosine increases heart rate by sup pressing parasympathetic and augmenting sympathetic components of heart rat e variability. High-frequency (P-H; 0. 15-0.50 Hz) and low-frequency (P-L; 0.05-0.15 Hz) components of heart rate variability total power (PT) Were de termined by spectral analysis. The ratios P-H/P-T and P-L/P-H respectively were used to estimate parasympathetic and sympathetic input to the sino-atr ial node. Heart rate was recorded before and during a 5 min intravenous inf usion of adenosine (140 mu g.min(-1) kg(-1)) in seven healthy men. Adenosin e did not affect blood pressure, but increased heart rate by 33 +/- 6 beats /min, and reduced P-T P-H P-L and P-H/P-T. In contrast, there was an increa se in P-L/P-H. In a second experiment in nine men, brachial artery infusion of adenosine (15 mu g.min(-1) 100 ml(-1) forearm tissue) increased heart r ate by 3 beats/min, had no effect on P-T, P-H, P(L)or P-H/P-T, yet increase d P-L/P-H. Intra-arterial adenosine exerts a modest effect on heart rate by modulating cardiac sympathetic indices, without affecting parasympathetic indices, of heart rate variability, whereas intravenous infusion of adenosi ne reduces heart rate variability and raises heart rate by decreasing paras ympathetic and increasing cardiac sympathetic tone. These reflex effects ma y become clinically relevant during adenosine stress testing, or when endog enous adenosine is increased, such as during ischaemia, exercise or vasodep ressor reactions, or in heart failure.