Effects of reducing sympathetic activities on acute myocardial ischemia in cats

The importance of the sympathetic nervous system in the genesis of ventricular arrhythmias associated with acute myocardial ischemia (AMI) was assessed in urethane-chloralose anesthetized cats. AMI was created by a ligation of the left anterior descending coronary artery. All control cats developed ventricular tachyarrhythmia (VT), ventricular fibrillation (VF), bradycardia and hypotension, resulting in 50% mortality. In other groups the paramedian reticular nucleus (PRN) was intermittently stimulated to inhibit the sympathetic nervous system. Both sides of the stellate ganglia (SG) or adrenal glands (AG) were removed to exclude direct effects of cardiac sympathetic nerve or indirect effects of circulatory catecholamines from the adrenal medulla on the heart, respectively. AMI did not affect plasma norepinephrine (NE) and epinephrine (EPI) concentrations in all groups. However, NE concentration was higher in SG removed but lower in AG removed group. Removal of SG and stimulation of PRN significantly reduced arrhythmia score and the incidence of VT, VF and mortality. Removal of AG appeared to be less effective. These findings suggest that cardiac sympathetic innervation is more important than neural and adrenal catecholamine secretions in the plasma.