![]() Bipolar electrode pairs were sutured to the epicardium of both atrial appendages and the ventricular apex. Additionally, in some animals, histologic sections proved that the excised tissue contained the entire SA node. ![]() Successful excision of the SA node was verified intraoperatively by ECG recordings. ![]() was employed to excise atrial tissue (1.5 x 0.7 cm) from the rostral end of the sulcus terminalis and the junction with the superior vena cava ( Figure 1). Briefly, with approval of the Institutional Animal Care Committee, a right thoracotomy was performed in eight mongrel dogs (18.5–21 kg). The methodology was similar to that reported previously, with changes pertaining to the excision of the SA node. Such knowledge should have relevance to the anesthetic management of patients with known or suspected SA node dysfunction. Although volatile anesthetic agents are known to modify SA nodal automatically through direct effects and the modification of autonomic reflexes, their effects on spontaneous automaticity and recovery from overdrive suppression of subsidiary atrial pacemakers in vivo remain to be elucidated. It has been demonstrated that excision of the high rostral portion of the canine sulcus terminalis ultimately produced permanent atrial escape rhythms, after the subsidiary atrial pacemakers adapted to the lack of overdrive suppression by the SA node, thus permitting studies in vivo over an extended period without competition from pacemakers with greater automatically. Removal of the SA node is necessary to further characterize the properties of subsidiary pacemakers in conscious and anesthetized dogs, because it enables suppressed pacemakers to assume permanent control of the heart rhythm. ![]()
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