Depression of the heart by quinidine and its treatment

Poisoning due to class IA antiarrhythmic drugs. Quinidine, procainamide and disopyramide

Quinidine, procainamide and disopyramide are antiarrhythmic drugs in the class 1A category. These drugs have a low toxic to therapeutic ratio, and their use is associated with a number of serious adverse effects during long term therapy and life-threatening sequelae following acute overdose. Class 1A agents inhibit the fast inward sodium current and decrease the maximum rate of rise and amplitude of the cardiac action potential. Prolonged Q-T interval and, to a lesser extent, QRS duration may be observed at therapeutic concentrations of quinidine. With increasing plasma concentrations, progressive depression of automaticity and conduction velocity occur. 'Quinidine syncope' (a transient loss of consciousness due to paroxysmal ventricular tachycardia, frequently of the torsade de pointes type) occurs with therapeutic dosing, often in the first few days of therapy. Extracardiac adverse effects of quinidine include potentially intolerable gastrointestinal effects and hypersensitivity reactions such as fever, rash, blood dyscrasias and hepatitis. Procainamide produces electrophysiological changes that are similar to those of quinidine, although Q-T interval prolongation with the former is less pronounced at therapeutic concentrations. Hypersensitivity reactions including fever, rash and (more seriously) agranulocytosis are associated with procainamide, and a frequent adverse effect requiring cessation of therapy is the development of systemic lupus erythematosus. Of the 3 drugs, disopyramide has the most pronounced negative inotropic effects, which are especially significant in patients with pre-existing left ventricular dysfunction. As with quinidine, unexpected 'disopyramide syncope' at therapeutic concentrations has been described. Anticholinergic side effects are common with this drug and may require cessation of therapy. Disopyramide therapy may unpredictably induce severe hypoglycaemia. Severe intoxication with the class 1A agents may result from acute accidental or intentional overdose, or from accumulation of the drugs during long term therapy. Acute overdose can result in severe disturbances of cardiac conduction and hypotension, frequently accompanied by central nervous system toxicity. Decreased renal function can cause significant accumulation of procainamide and its active metabolite acecainide (N-acetyl-procainamide), resulting in severe intoxication. Mild to moderate renal dysfunction is less likely to lead to quinidine or disopyramide intoxication, unless renal failure is severe or concurrent hepatic dysfunction is present. Management of acute intoxication with class 1A drugs includes gut decontamination with provision of respiratory support and treatment of seizures as needed. Hypertonic sodium bicarbonate, by antagonising the inhibitory effect of quinidine on sodium conductance, may reverse many or all manifestations of cardiovascular toxicity.(ABSTRACT TRUNCATED AT 400 WORDS)

Cardiovascular collapse associated with disopyramide therapy

Five patients with severe left ventricular failure, renal insufficiency, and recurrent ventricular tachycardia had cardiovascular collapse and died eight hours to 23 days after initiation of the usual doses of disopyramide. Three patients had recent myocardial infarction (12 to 33 days), and one had severe congestive cardiomyopathy. ECG changes antedated appearance of cardiovascular collapse and consisted of lengthening of the QRS (0.10 plus or minus 0.02 to 0.22 plus or minus 0.09; P less than 0.025) and the QTc duration (0.44 plus or minus 0.04 to 0.56 plus or minus 0.09; P less than 0.05). Sinus bradycardia or varying degrees of atrioventricular block or both occurred in all patients. Terminal disopyramide blood concentration (4.9 and 8.1 micrograms/ml) were available in two patients. A syndrome of progressive lengthening of ventricular depolarization and repolarization terminating in cardiovascular collapse and death associated with disopyramide is described. In addition, a high incidence of sinus bradycardia, atrioventricular conduction disturbances, or both was also noted. Disopyramide is contraindicated in patients with severe heart failure and renal insufficiency. Progressive widening of the QRS complex or the QT interval may presage appearance of severe myocardial dysfunction.

The management of acute quinidine intoxication

A 16-year-old patient survived severe intoxication with quinidine. Hypotension, rapidly progressing to oliguria and shock, was resistant to the usual therapeutic interventions but responded favorably to the use of an intra-aortic balloon pump. Some hemodynamic implications are discussed. Pulmonary edema occurred and was treated with positive end-expiratory pressure. Electrocardiographic disturbances in conduction, transient bradycardia and recurrent ventricular arrhythmias characterized the initial 36-hour critical period. Unexplained electrolyte abnormalities occurred and further complicated management.

Relationship Between Adrenergic Activity and Cardiac Actions of Quinidine

Unanesthetized dogs with complete heart block were used to explore the relationship between adrenergic activity and quinidine action on the heart. After vagolysis, quinidine still increased both the atrial and ventricular rates. Following reduction in adrenergic activity by reserpine, hexamethonium, or surgical sympathectomy, the atrial and ventricular pacemakers were depressed. After sympathetic activity had been reduced by a combination of hexamethonium and reserpine, quinidine caused profound pacemaker depression and sometimes ventricular asystole. Quinidine produced coupling and occasionally runs of ventricular tachycardia independent of the level of sympathetic activity. There was no significant prolongation of the QRS time by quinidine in doses of 5 and 10 mg./Kg. Both the development of ectopic pacemakers and the depression of pacemaker activity of quinidine were dose dependent.

Quinidine intoxication treated by isoproterenol (Isuprel)

Images