ATRIAL-NATRIURETIC-FACTOR RELEASE DURING RAPID VENTRICULAR PACING - INTERPLAY BETWEEN AUTONOMIC AND HEMODYNAMIC STIMULANTS

Plasma levels of atrial natriuretic factor (ANF) and norepinephrine ar e markedly elevated during episodes of ventricular tachycardia. Althou gh atrial distention appears to be the major stimulus for ANF release, reflex changes in autonomic tone might also contribute. Plasma ANF an d norepinephrine levels, sinus node cycle length, systolic blood press ure, and mean right atrial pressure were therefore assessed during rap id right ventricular pacing at 150 beats/min for 10 minutes. In five p atients (group 1) observations were made without autonomic blockade, a nd another five patients (group 2) had ventricular pacing after cardia c autonomic blockade. In group 1 systolic blood pressure fell during v entricular pacing from 122 +/- 4 to 105 +/- 5 mm Hg (p < 0.02), norepi nephrine levels increased from 195 +/- 26 to 411 +/- 71 pg/ml (p < 0.0 2), and sinus node cycle length decreased from 936 +/- 99 to 688 +/- 5 8 msec (p < 0.02). Right atrial pressure was elevated from 2.6 +/- 0.6 to 7.4 +/- 0.6 mm Hg (p < 0.02), and ANF levels increased from 161 +/ - 23 to 240 +/- 26 pg/ml (p < 0.05). Whereas systolic blood pressure, norepinephrine, sinus cycle length, and right atrial pressure returned promptly to baseline levels when ventricular pacing was stopped, ANF levels continued to rise (296 +/- 37 pg/ml; p < 0.05). Compared with g roup 1, ventricular pacing in group 2 induced a greater reduction in s ystolic blood pressure (19 +/- 2% vs 8 +/- 5%; p < 0.05) and a more ma rked increase in norepinephrine levels (271 +/- 52% vs 111 +/- 22%; p < 0.05), but because of cardiac autonomic blockade the decline in sinu s cycle length was attenuated (8 +/- 2% vs 33 +/- 5%; p < 0.05). Inasm uch as there was no significant difference between the increase in rig ht atrial pressure and ANF levels, it was concluded that changes in au tonomic tone during ventricular tachycardia do not significantly influ ence ANF release.