Comparison of the effects of intravenous LNC-834, a new antiarrhythmic agent, and quinidine in canine models of arrhythmia

Suppression of inducible ventricular arrhythmias by intravenous azimilide in dogs with previous myocardial infarction

The class III antiarrhythmics azimilide dihydrochloride and dl-sotalol were evaluated for ability to suppress induction of ventricular tachyarrhythmias (VT) in anesthetized, male mongrel dogs 4-6 days after surgical infarction of the left ventricle (LV) produced by ligation/reperfusion of the left anterior descending coronary artery. Postmortem infarcts averaged 28.2 +/- 3.3% and 27.5 +/- 3.9% of the LV for azimilide- and sotalol-treated dogs, respectively. Both agents (0.3-30 mg/kg i.v.) increased ventricular effective refractory period as a function of dose in LV normal and infarcted zones without increasing conduction time. Azimilide was well tolerated hemodynamically up to 30 mg/kg i.v., whereas sotalol produced a significant and dose-related decrease in both blood pressure and heart rate. Azimilide was effective in five (56%) of nine dogs in preventing induction of ventricular arrhythmias by programmed electrical stimulation (PES) at doses from 1 to 30 mg/kg. Efficacy was seen for nonsustained and sustained VT and for ventricular fibrillation. Although sotalol (0.3-10 mg/kg) was effective in all five VT dogs tested, one of two nonsustained ventricular tachyarrhythmia (NSVT) dogs and two of three sustained ventricular tachyarrhythmia (SVT) dogs were reinducible with the baseline arrhythmia at doses higher than the effective dose, and one dog died after 30 mg/kg of sotalol. Both agents increased the cycle length of VT. Thus azimilide simultaneously increased refractoriness and provided antiarrhythmic efficacy as suppression of PES-induced ventricular arrhythmias in infarcted dogs without the hemodynamic depression seen with sotalol.

Proarrhythmic effects of a quinidine analog in dogs with chronic A-V block

The proarrhythmic effects of 3-hydroxy-hydroquinidine (3-OH-HQ) and quinidine were compared in a canine model of QT-dependent ventricular arrhythmias. Eight hypokalemic ([K+] < or = 3.2 mmol/l) dogs with AV block (around 45 bpm) were given either drug in a randomized order at 2-day intervals. Each drug was given as two 1 hour doses, with a bolus (low dose: 5 mg/kg or high dose: 10 mg/kg) plus infusion (25 or 50 micrograms/kg/min) protocol. Propranolol infusion was combined with a third hour of the high dose infusion. Electrophysiologic measurements were performed at baseline and 30 minutes after the beginning of each dose and propranolol infusion, and proarrhythmic events were recorded 30 minutes before and during the experiment. Neither drugs altered the ventricular cycle length. Quinidine and 3-OH-HQ prolonged the QT interval similarly and significantly when paced at 60 bpm after the low dose (+39 +/- 18 and +28 +/- 22 msec, respectively) and after the high dose (+51 +/- 29 and +50 +/- 22 msec). Quinidine was more arrhythmogenic than 3-OH-HQ: 7/8 dogs (p < or = 0.05) developed ventricular arrhythmias (isolated, repetitive ventricular beats, or polymorphic ventricular tachycardias) during quinidine infusion (low dose: 4 dogs) compared to 3/8 dogs (NS) during 3-OH-HQ infusion (low dose: 1 dog). Addition of propranolol-induced bradycardia (around 30 bpm) caused torsades de pointes (wave burst arrhythmias) or polymorphic ventricular tachycardias after both drugs (in 3 dogs after quinidine and in 2 dogs after 3-OH-HQ). Thus 3-OH-HQ was slightly less arrhythmogenic than quinidine in this model of torsades de pointes, but the addition of an extra favouring factor (bradycardia) reduced that difference.