Although β-adrenergic blockade is beneficial in heart failure, inhibition of central sympathetic outflow using moxonidine has been associated with increased mortality. In the present study, we studied the acute effects of the imidazoline-receptor agonist moxonidine on haemodynamics, NA (noradrenaline) kinetics and myocardial metabolism. Fifteen patients with CHF (chronic heart failure) were randomized to a single dose of 0.6 mg of sustained-release moxonidine or matching placebo. Haemodynamics, NA kinetics and myocardial metabolism were studied over a 2.5 h time period. There was a significant reduction in pulmonary and systemic arterial pressures, together with a decrease in cardiac index in the moxonidine group. Furthermore, there was a simultaneous reduction in systemic and cardiac net spillover of NA in the moxonidine group. Analysis of myocardial consumption of substrates in the moxonidine group showed a significant increase in non-esterified fatty acid consumption and a possible trend towards an increase in myocardial oxygen consumption compared with the placebo group (P=0.16). We conclude that a single dose of moxonidine (0.6 mg) in patients already treated with a β-blocker reduced cardiac and overall sympathetic activity. The finding of increased lipid consumption without decreased myocardial oxygen consumption indicates a lack of positive effects on myocardial metabolism under these conditions. We suggest this might be a reason for the failure of moxonidine to prevent deaths in long-term studies in CHF.

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