Sustained left ansae subclaviae stimulation for a 5-hour period inhibits cesium-induced ventricular arrhythmogenesis in rabbits

The acute stimulation of the left ansae subclaviae (LAS) augments cesium ch loride (Cs)- induced early afterdepolarizations (EADs) and ventricular arrh ythmias. However, the effect of sustained cardiac sympathetic nerve stimula tion on Cs-induced arrhythmogenesis remains to be elucidated. Three protoco ls were used. In protocol A, seven rabbits received continuous LAS stimulat ion for 5 h (study group), and were then given bolus injections of Cs at 5- min intervals (initial dose 1.5 mmol/kg, followed by repetitive doses 1 mmo l/kg). Another eight rabbits received the same dose of Cs after a 5-h obser vation period without LAS stimulation (control group). The effects of 2 h o f LAS stimulation were also assessed in five rabbits of each group. In prot ocol B, a bolus injection of Cs (1 mmol/kg) was administered during atrial pacing (cycle length: 250 ms) after a 5-h period with (study group, n = 5) or without (control group, n = 5) LAS stimulation, and the amplitude of Cs- induced EADs was measured. In protocol C, a bolus injection of isoprotereno l (0.05 mg/kg) was given after a 5-h period with (study group, n = 5) or wi thout (control group, n = 5) LAS stimulation to assess the sensitivity to P -adrenergic stimulation. In protocol A, the cumulative doses of Cs required for the induction of ventricular tachycardia (VT) and fibrillation (VF) we re significantly greater in the study group than in the control group (4.4 +/- 0.1. v 2.8 +/- 0.3 mmol/kg for VT, P<0.05; 5.8 +/- 0.3 v 4.1 +/- 0.4 mm ol/kg for VF, P<0.05). However, 2 h of LAS stimulation did not influence th e cumulative doses of Cs required for the induction of VT and VF. In protoc ol B, the amplitude of Cs-induced EADs was significantly lower in the study group than in the control group. In protocol C, the increase in rate-press ure product by isoproterenol was significantly less in study than in contro l groups (3492 +/- 612 v 6504 +/- 829 P<0.05). These results suggest that s ustained LAS stimulation exerts a protective effect against Cs-induced arrh ythmogenesis in the rabbit heart, which may be partially explained by desen sitization to the beta-adrenergic stimulation. (C) 1998 Academic Press.