Efficacy of pentamidine analogue 6 in dogs with chronic atrial fibrillation

BACKGROUND: The inward rectifier inhibitor pentamidine analogue 6 (PA-6) is effective in cardioversion of goats with persistent rapid pacing induced atrial fibrillation (AF) and is not proarrhythmic in dogs with experimental chronic 3rd-degree AV block. Efficacy and safety in the clinical setting are unknown. HYPOTHESIS: That PA-6 would be effective in converting AF to sinus rhythm (SR) in dogs with naturally occurring AF, without the presence of overt adverse effects. ANIMALS: Ten client-owned large and giant breed dogs. METHODS: for a maximum of 50 minutes in conscious dogs. Standard 6 lead limb ECG was recorded during the infusion. Visible and audible signs of adverse effects were scored during the entire procedure. RESULTS: PA-6 did not induce changes in QRS duration (54.7 ± 4.6 versus 56.7 ± 6.1 ms, P = .42), QTc interval (241.1 ± 19.5 versus 258.7 ± 19.8 ms, P = .061) or RR interval (363.4 ± 84.6 versus 440.8 ± 96.3 ms, P = .072) at the end of the bolus. No cardioversion to SR was observed in any dog. Three dogs displayed no adverse effects. Five dogs had premature ventricular depolarizations during PA-6 infusion on the ECG. Respiratory distress with laryngeal stridor, subtle muscle twitching, and mild generalized muscular weakness were noncardiac adverse effects observed in 5 dogs. Adverse effects resolved spontaneously. CONCLUSIONS AND CLINICAL IMPORTANCE: Chronic naturally occurring AF in large and giant breed dogs could not be cardioverted to SR by PA-6.