The Journal of Thoracic and Cardiovascular Surgery, Vol 103, 1192-1199, Copyright © 1992 by The American Association for Thoracic Surgery and The Western Thoracic Surgical Association
Influences of cardiopulmonary bypass, temperature, cardioplegia, and topical hypothermia on cardiac innervation
DA Murphy and JA Armour
Department of Surgery, Faculty of Medicine, Dalhousie University, Halifax, Nova Scotia, Canada.
The effects of normothermic and hypothermic cardiopulmonary bypass,
crossclamping of the aortic root, cold cardioplegia, as well as epicardial
application of iced slush, on the efficacy of the efferent sympathetic
nervous system to augment the heart and the efferent parasympathetic
nervous system to depress the heart were studied in anesthetized dogs.
Cardiac rate and force are augmented by stimulation of the intrathoracic
efferent sympathetic nervous system and reduced by stimulation of the
intrathoracic efferent parasympathetic nervous system. After
cardiopulmonary bypass, which included systemic and topical hypothermia,
aortic crossclamping, and crystalloid cardioplegia, the augmentor effects
of the efferent sympathetic nervous system were obtunded whereas the
depressor effects exerted by the efferent parasympathetic nervous system
were not. Direct cardiac myocyte augmentor responses induced by
isoproterenol were unaffected by these interventions. Normothermic
cardiopulmonary bypass, hypothermic cardiopulmonary bypass, crossclamping
of the aorta, or cold cardioplegia did not result in blunting of the
efferent sympathetic cardiac nervous system. Significant blunting of
cardiac augmentation induced by the efferent sympathetic nervous system
occurred after topical application of iced slush alone. These data
demonstrate that blunting of the efferent sympathetic, but not
parasympathetic, innervation of the heart occurs after cardiopulmonary
bypass, which presumably is primarily due to altering the function of
subepicardial efferent sympathetic axons by topical hypothermia and not due
to altered cardiac myocyte function. These data imply that after
cardiopulmonary bypass involving the procedures described, the ability of
the efferent sympathetic nervous system to support cardiac rate and force
is transiently impaired.
