Quinidine sulfate administration in horses with atrial fibrillation reduced median dominant frequency from 6.4 Hz to 3.0 Hz immediately before conversion to sinus rhythm, with an EC50 of 0.78 μg/mL.
Does quinidine sulfate reduce dominant frequency in Thoroughbred horses with atrial fibrillation?
A plasma quinidine concentration of 2.6 μg/mL is predicted to achieve a dominant frequency of 3.0 Hz, which may represent a target concentration for conversion to sinus rhythm in horses with atrial fibrillation.
ABSTRACT Quinidine has long been used for the pharmacological treatment of atrial fibrillation (AF) in horses; however, the plasma concentration required for conversion to sinus rhythm remains unclear. Dominant frequency (DF), derived from surface electrocardiograms, reflects atrial activation rate during AF. This study aimed to quantify the relationship between plasma quinidine concentration and DF using a pharmacokinetic/pharmacodynamic (PK/PD) approach. Ten Thoroughbred horses with naturally occurring AF received quinidine sulfate via a nasogastric tube. Plasma quinidine concentrations and DF values, calculated from digitized atrial fibrillatory segments, were measured during treatment. PK/PD was analyzed using a sigmoid inhibitory E max model, with typical parameters including a baseline DF of 6.27 Hz, a maximal DF reduction of 3.63 Hz, a theoretical minimum DF of 2.64 Hz, an EC 50 of 0.78 μg/mL, and a Hill coefficient of 1.81. Nine horses converted to sinus rhythm, with median DF decreasing from 6.4 Hz to 3.0 Hz immediately before conversion. Model simulations indicated a pharmacodynamic plateau, with an increase in plasma quinidine concentration from 4 to 5 μg/mL resulting in only a 0.06‐Hz reduction in DF. A model‐predicted plasma quinidine concentration of 2.6 μg/mL achieved a DF of 3.0 Hz and may represent a target concentration for conversion.
Kuroda et al. (Thu,) conducted a other in Atrial fibrillation (n=10). Quinidine sulfate was evaluated on Relationship between plasma quinidine concentration and dominant frequency (DF). Quinidine sulfate administration in horses with atrial fibrillation reduced median dominant frequency from 6.4 Hz to 3.0 Hz immediately before conversion to sinus rhythm, with an EC50 of 0.78 μg/mL.
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