1. To determine the influence of loss of atrioventricular synchrony on release of atrial natriuretic peptide (ANP), plasma ANP concentrations were measured by radioreceptor assay in 16 patients during sequential and ventricular cardiac pacing at normal heart rates.

2. Ventricular pacing induced an increase in plasma ANP concentrations (means ± SEM) from 44 ± 3 to 104 ± 4 pmol/l (P < 0.01) in 11 patients in whom systemic blood pressure was maintained.

3. In contrast, when ventricular pacing was associated with a fall in blood pressure (five patients), ANP levels (means ± SEM) fell from 68 ± 6 to 14 ± 4 pmol/l (n = 5, P < 0.05) within 5 min, despite an increase in atrial pressure. Plasma catecholamines also rose significantly in these latter patients.

4. We conclude that when loss of atrioventricular synchrony is well tolerated haemodynamically, cardiac release of ANP is increased in keeping with elevation in atrial pressure. However, the fall in plasma ANP concentration observed when ventricular pacing produces a fall in blood pressure suggests that in addition to atrial pressure, ANP release may be influenced by negative feedback mechanisms, possibly involving the baroreflex and autonomic nervous system.

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