Epinephrine antiarrhythmic effects

Lidocaine is used in cardiovascular medicine for its antiarrhythmic properties (see Ch. 12). More recently, studies have looked at the i.v. administration of lidocaine to horses with colic (see Ch. 6). It appears that i.v. lidocaine (without epinephrine (adrenaline)) may have some desirable effects on jejunal distension and peritoneal fluid accumulation and is well-tolerated periop-eratively in horses with colic (Brianceau et al 2002). In addition, i.v. lidocaine reduced the halothane MAC significantly (Doherty Frazier 1998) in ponies. 

Cardiovascular System Following systemic absorption, local anesthetics decrease electrical excitabdity, conduction rate, and force of contraction. Most local anesthetics also cause arteriolar dilation. Untoward cardiovascular effects usually are seen only after high systemic concentrations are attained and effects on the CNS are produced. However, on rare occasions, lower doses of some local anesthetics wUl cause cardiovascular collapse and death, probably due to either an action on the pacemaker or the sudden onset of ventricular fibrillation. Ventricular tachycardia and fibrillation are relatively uncommon consequences of local anesthetics other than bupivacaine. The use of local anesthetics as antiarrhythmic drugs is discussed in Chapter 34. Untoward cardiovascular effects of local anesthetic agents may result from their inadvertent intravascular administration, especially if epinephrine also is present. 

Lycorine (1) is an analgesic, more so than aspirin, and a hypotensive (489,490), as are caranine (10) and galanthine (7). The analgesic activity exhibited by the Amaryllidaceae alkaloids is attributed to their resemblance to the morphine and codeine skeletons. Lycorine also has antiarrhythmic action, and lycorine hydrochloride is a strong broneholytic (30). In fact, lycorine shows a relaxant effect on an isolated epinephrine-preeontracted pulmonary artery and increases contractility and the rate of an isolated perfused heart. These effects are mediated by stimulation of S-adrenergic receptors (491). 

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