Reversible blockade of cardiac efferents with procaine instilled into the pericardium of cats

The blocking of afferent signals from the heart by the instillation of local anaesthetics into the pericardium has frequently been used for studying cardiac reflexes. Yet no attempts have been made to define what effects this has on efferent cardiac drive. Therefore, in nine chloralosed cats with open chests and catheters sewn into the pericardium the procaine concentrations were determined which would block the heart rate responses to electrostimulation of the vagi nerves or the stellate ganglia. The procaine effects on arterial pressure and left ventricular peak positive dP/dt were also evaluated and in 11 cats the vagolytic effects of atropine (0.25 mg . kg-1, intravenous) and intrapericardial procaine (0.1%) were compared. As little as 0.05% procaine attenuated the bradycardia associated with stimulation of the stellate ganglia by only about 30%. Virtual elimination of both sympathetic and vagal drive was achieved with 0.5% procaine having only mild effects on blood pressure and left ventricular dP/dt. Atropine (0.25 mg . kg-1, intravenously) and procaine (0.1% intrapericardially) affected heart rate equally. With procaine in the pericardium it is possible to reversibly and selectively block cardiac efferents and to separate vagal and sympathetic drive by choosing the appropriate concentration of the local anaesthetic.