Characteristics of the acute rise of atrial natriuretic factor during ventricular pacing

Previous studies have shown that peripheral venous levels of atrial natriuretic factor (ANF) are elevated during ventricular pacing as a result of asynchrony of atrial and ventricular contraction. However, the pattern by which ANF rises following institution of ventricular pacing has not been fully established and its physiologic consequences are unclear.

Eight ambulatory patients in stable condition with dual-chamber pacemakers were studied. The pacemaker was reprogrammed from the dual-chamber to the ventricular pacing mode for 3 h, during which serial measurements were made of BP, heart rate and rhythm, levels of ANF, and plasma renin activity (PRA).

ANF levels rose markedly but slowly following the onset of ventricular pacing, reaching levels as high as 694% of control. The rise occurred over the course of 120 min, at which time the average value for the group plateaued at 82.5 +/- 22.1 fmol/mL (mean +/- SEM) vs 25.3 +/- 4.5 fmol/mL at control (p < 0.01); there was, however, marked variability in individual responses. By contrast, levels of PRA remained remarkably stable. Average BP changes were small, although there was a trend in the later part of the study for systolic pressure to decrease.

ANF levels rise markedly but gradually after institution of ventricular pacing and, hence, acute pacing studies must account for this delay in their design. The physiologic importance of the rise in ANF should be evaluated further since the rise in peptide levels may be associated with a decrease in systolic BP.