system
Medical AI Inquiry: You was designed to assist in medical decision-making based on the provided user questions. It is crucial to provide accurate and comprehensive information to receive a well-informed response.  Labels: OBJECTIVE, METHODS, RESULTS. Meshes: Adrenergic Uptake Inhibitors, Adrenergic beta-Antagonists, Analysis of Variance, Animals, Atenolol, Cardiac Pacing, Artificial, Desipramine, Electric Stimulation, Electrocardiography, Female, Heart Failure, Lung, Male, Myocardial Infarction, Myocardium, Norepinephrine, Perfusion, Potassium, Propanolamines, Rats, Rats, Sprague-Dawley, Sex, Statistics, Nonparametric, Sympathetic Nervous System, Tachycardia, Ventricular.
user
Does sympathetic activation trigger ventricular arrhythmias in rat heart with chronic infarction and failure? Context: To seek direct evidence for a cause-effect relation between sympathetic activation and arrhythmogenesis. Rats underwent open-chest surgery with either coronary artery occlusion or sham operation, and were studied 8 weeks later using in situ heart perfusion and nerve stimulation methods. Infarcted rats showed cardiac functional impairment and increased heart and lung weight. The extent of these changes correlated well with infarct size (IS). In in situ perfused hearts, sympathetic nerve stimulation (2 and 4 Hz, 45 s duration) induced a frequency-dependent release of norepinephrine (NE). NE release was lower in MI than that in control groups. In hearts with large IS (> or = 40%, n = 19) ventricular arrhythmias were rare at baseline, but nerve stimulation evoked the onset of ventricular premature beats (95%), tachycardia (37%) and fibrillation (26%), IS and stimulation frequency were key determinants for the inducibility of arrhythmias. Lower K- concentration enhanced arrhythmia inducibility. beta-blockade inhibited the frequency of arrhythmias produced by nerve stimulation.
assistant
In infarcted rat hearts sympathetic activation is a potent trigger for the onset of ventricular tachyarrhythmias. Final Decision: yes