Disopyramide (INN, trade names Norpace and Rythmodan) is an antiarrhythmic medication used in the treatment of ventricular tachycardia. It is a sodium channel blocker and therefore classified as a Class 1a anti-arrhythmic agent. Disopyramide has a negative inotropic effect on the ventricular myocardium, significantly decreasing the contractility. Disopyramide also has an anticholinergic effect on the heart which accounts for many adverse side effects. Disopyramide is available in both oral and intravenous forms, and has a low degree of toxicity. Mechanism of action
Disopyramides Class 1a activity is similar to that of quinidine in that it targets sodium channels to inhibit conduction. Disopyramide depresses the increase in sodium permeability of the cardiac myocyte during Phase 0 of the cardiac action potential, in turn decreasing the inward sodium current. This results in an increased threshold for excitation and a decreased upstroke velocity. Disopyramide prolongs the PR interval by lengthening both the QRS and P wave duration. This effect is particularly well suited in the treatment of ventricular tachycardia as it slows the action potential propagation through the atria to the ventricles. Disopyramide does not act as a blocking agent for beta or alpha adrenergic receptors, but does have a significant negative inotropic effect on the ventricular myocardium. As a result, the use of disopyramide may reduce contractile force up to 42% at low doses and up to 100% in higher doses compared to quinidine.Levites proposed a possible secondary mode of action for disopyramide, against reentrant arrhythmias after an ischemic insult.
Treatment
Treatment is a relatively simple surgery in which excess skin of the outer lids is removed or tendons and muscles are shortened with one or two stitches. General anesthesia is sometimes used before local anesthetics are injected into the muscles around the eye. Prognosis is excellent if surgery is performed before the cornea is damaged. Entropion in other species
Entropion has been documented in most dog breeds, although there are some breeds (particularly purebreds) that are more commonly affected than others. These include the Akita, Pug, Chow Chow, Shar Pei, St. Bernard, Cocker Spaniel, Boxer, English Springer Spaniel, Welsh Springer Spaniel, Labrador Retriever, Cavalier King Charles Spaniel, Neapolitan Mastiff, Bull Mastiff, Great Dane, Irish Setter, Shiba Inu, Rottweiler, Poodle and particularly Bloodhound. The condition is usually present by six months of age. If left untreated, the condition can cause such trauma to the eye that it will require removal. Entropion has also been seen in cat breeds. Typically it is secondary to trauma or infection leading to chronic eyelid changes. It is also seen secondary to enophthalmos. Primary entropion might also be encountered : the brachycephalic breeds (mostly the Persian) and the Maine Coon are predisposed.Upper-lid entropion involves the eyelashes rubbing on the eye, but the lower lid usually has no eyelashes, so little or no hair rubs on the eye. Surgical correction is used in more severe cases. A number of techniques for surgical correction exist.