The effect of bretylium tosylate on the normal and digitalis-sensitized dog heart

Digitalis glycosides: a discussion of the similarities and differences in actions and existing controversies

The writing of this review was initiated to answer the question of whether differences in the actions of the various digitalis glycosides exist and to discuss current controversies in the research area of the digitalis glycosides. Data obtained in our laboratory indicated that the effect of digoxin on postganglionic cardiac sympathetic neural discharge in the minute prior to the occurrence of arrhythmia differed from that of ouabain. This raised the question of whether data published in other laboratories would support the contention that differences in glycosides do exist. To answer this question, a review of the literature was begun. Our survey of these studies are cited in the tables of this review. These tables summarize the actions of glycosides in vivo and in vitro in different animal models. The reader should bear in mind that the data included within the tables do not represent an inclusive summary of all studies in the literature. For detailed review articles, the reader is referred to the following references: Gillis et al; Gillis and Quest; Roberts et al; Lathers and Roberts; Farah and Alousi; Benthe; Levitt et al; Smith and Haber; Somberg; Lee and Klaus; Mason; Schwartz. Furthermore the summary of the results for each particular study cited in the table may not, in all cases, include each finding of the published data. Nevertheless, the tables do provide a summary of data obtained in various species with different glycosides in several different areas of research, and as such, represent an abridged compendium for the research working in the field of digitalis glycosides. This review has been organized firstly to consider glycoside-induced alterations in the autonomic nervous system and, secondly, to examine their direct actions on the heart.

Bretylium in severe ventricular arrhythmias associated with digitalis intoxication

Bretylium has been well-recognized as an effective antiarrhythmic agent for acute ventricular arrhythmias, but its use is believed to be contraindicated in digitalis intoxication. We report of two patients in whom digitalis-induced malignant ventricular arrhythmias were refractory to lidocaine. One patient had had repeated episodes of ventricular fibrillation associated with digitoxin and quinidine intoxication, and one patient had had malignant premature ventricular beats associated with digoxin intoxication. Cardiac electrical activity was paced in both instances. In the two patients, ventricular arrhythmias rapidly resolved, and no side effect was encountered. These observations support the administration of bretylium for severe digitalis-induced ventricular arrhythmias.

Acute and chronic digitalis toxicity: presentation and treatment

Although digitalis toxicity is commonly encountered, it can easily be mistaken because of its many manifestations. Recognition of toxicity depends on an awareness of the difference between an acute digitalis overdose and chronic digitalis toxicity. The gastrointestinal, central nervous, and cardiac conduction systems are most commonly involved. Ventricular ectopy and arrhythmias are common with chronic toxicity, while disturbances of sinus impulse formation, A-V blocks, and nodal arrhythmias are seen with both acute and chronic digitalis toxicity. Treatment is mainly supportive, except in acute poisoning, in which case attempts must be made to clear as much drug as possible from the gastrointestinal tract.

Deleterious effects of bretylium in cats with digitalis-induced ventricular tachycardia

The effect of bretylium on ventricular tachycardia induced by digitalis was studied in Dialurethane-anesthetized cats with continuous monitoring of the electrocardiogram and arterial blood pressure. Ventricular tachycardia was produced by repeated injections of deslanoside (25 µg/kg) at 15 min intervals. Only one of eight animals showed conversion of ventricular tachycardia to sinus rhythm with bretylium administration (2-100 mg/kg i.v.). In each animal, bretylium increased the ventricular rate. The effect of bretylium (30 mg/kg i.v.) on duration of ventricular tachycardia induced by deslanoside (0.75 µg/kg/min) was also studied. Duration was shortened from 65 ± 8.0 min to 7 ± 1.0 min, but the reduction was due to the intervention of either ventricular fibrillation or severe hypotension caused by bretylium. Pretreatment with propranolol (0.5 mg/kg i.v.) prevented these deleterious effects and unmasked an antiarrhythmic effect of bretylium since duration of ventricular tachycardia was significantly shorter (40 ± 6.0 min) than the controls (65 ± 8.0 min). In addition, an antiarrhythmic effect of bretylium was noted when it was administered as a dose of 30 mg/kg ip to animals 24 and 4 hours prior to deslanoside intoxication; 231 µg/kg deslanoside were now required for inducing ventricular tachycardia as compared to 175 µg/kg deslanoside in controls. Thus, bretylium given alone during a digitalis-induced ventricular tachycardia increases both the rate of ventricular tachycardia and the likelihood of ventricular fibrillation. These deterious effects appear to be related to a norepinephrine-releasing action and may be avoided by either pretreatment with propranolol or administration of bretylium several hours prior to digitalis intoxication.

Response of resistant ventricular tachycardia to bretylium. Relation to site of ectopic focus and location of myocardial disease

Ventricular tachycardias were determined to be of either right-or left-sided origin in 25 patients whose arrhythmias were life-threatening and resistant to lidocaine and other antiarrhythmic drugs. All five patients with right ventricular tachycardia responded well to bretylium and survived. Eleven of 20 patients with left ventricular tachycardia did not do well. Four did not respond to bretylium but survived, five had no response and died, and two responded but died when hypotension prevented continued treatment. Eight of these 11 had acute anterior myocardial infarction or ischemia. Of nine patients with left ventricular tachycardia who responded well to bretylium and survived, only two had anterior infarction, and none had anterior ischemia. Because bretylium was efficacious in all patients with right ventricular tachycardia or inferior myocardial infarction in this study, it seems warranted to investigate further the relationship between drug responsiveness and the site of ectopic impulse formation and the location of myocardial disease.