Differential effects of cervical vagosympathetic and mediastinal nerve activation on atrial arrhythmia formation in dogs

To investigate the influence of the thoracic autonomic neuronal hierarchy on atrial arrhythmia formation, we compared the characteristics of atrial tachyarrhythmias induced by electrical stimulation of 1) the right vagosympathetic nerve complex at the cervical level and 2) the more caudal juxta-cardiac mediastinal nerves located on the anterior surface of the superior vena cava. Unipolar electrograms were recorded from 191 sites on the entire epicardial atrial surface and, in some experiments, from 63 right atrial endocardial sites. The sites of origin of initial beats at the onset of atrial tachyarrhythmias so induced were investigated analysing atrial activation maps. Neural effects on repolarization were determined by computing the integral surface subtended by unipolar recordings under basal conditions and at maximum neurally induced bradycardia, and calculating differences at each recording site. The mean area affected by nerve stimulation in all animals was significantly greater in response to vagosympathetic than mediastinal nerve stimulation. Atrial cycle length prolongation prior to tachyarrhythmia onset was more pronounced in response to vagosympathetic than mediastinal nerve stimulation. The earliest epicardial activations in early tachyarrhythmia beats were localized in the right atrial free wall and Bachmann bundle region in both cases, but with a higher incidence of double breakthroughs from septal sites of origin in response to vagosympathetic versus mediastinal nerve stimulation. Sites of early activation were associated with the areas of neurally induced repolarization changes. Thus, differential contributions are made to the electrophysiologic substrate of neurally induced atrial tachyarrhythmias depending on the pattern of engagement of neural elements within the autonomic neuronal hierarchy.