Myocardial performance after excision of the extrinsic cardiac nerves in the dog.

• The performance of the heart in the intact subject is determined by the complex interplay of cardiac and extracardiac factors; the initial length of the myocardial fibers and the state of activity of the cardiac autonomic nerves are most important. The profound changes in cardiac behavior that attend excitation of the cardiac autonomic nerves have led to the concept of neurogenic dominance in the control of cardiac output, particularly in situations that strongly constrain the cardiovascular system. This concept is basic to an evaluation of the mechanisms by which the heart responds to changes in the peripheral circulation and has important implications in clinical cardiac transplantation. In this review, the behavior of the denervated heart in different stressful situations is considered; the presentation is limited to studies in which dogs have been chronically deprived of both sympathetic and parasym-pathetic nerves. The role of cardiac receptors and their afferent innervation has recently been reviewed and is not discussed in this paper (1, 2). The four major techniques of cardiac denerva-tion currently used are described briefly, because the method of denervation will influence the results obtained. (1) According to the methods of Gasser and Meek (3) and of Ashkar and Hamilton (4), the stell-late ganglia and thoracic paravertebral sympathetic chains are bilaterally excised from T-l to T-4. The right vagus nerve is sectioned distal to the right recurrent laryngeal nerve. During a second operation, the left vagus nerve is sectioned in the neck. Some cardiac sympathetic fibers remain bia-ble but decentralized, and the myocardial content of catecholamines is reduced to a varying degree. Supersensitivity to catecholamines does not develop. The lungs and viscera are vagally denervated, resulting in altered respiratory dynamics, gastroin-testinal disturbances, and loss in body weight. Vagal cardiopulmonary afferent nerves are interrupted. (2) Complete cardiac denervation is assured after orthotopic autografts or allografts. This tech-niquerequires cardiac bypass and results in significant morbidity and mortality. Sympathetic dener-vation is postganglionic, and the heart is depleted of and becomes supersensitive to catecholamines. Pulmonary afferent fibers are preserved, but afferent fibers that course along the aorta, the main pulmonary artery, or the superior vena cava are interrupted. Dependong on the technique used, afferent fibers from receptors in the pulmonary veins, posterior atrial wall, and ostia of the vena cava may (5) or may not (6) be preserved. After transplantation, variability in the functional integrity of the donor sinus node has been noted. (3) …