Our goal was to determine the effect of regadenoson (a novel A2A adenosine receptor agonist) on the QT interval in conscious dogs. Eleven mongrel dogs were chronically instrumented for measurements of blood pressure and ECG. Regadenoson (2.5, 5 and 10 μg/kg, IV) caused a dose-dependent QT interval shortening (ΔQT: 14±3, 24±5 and 27±5 ms, mean±SEM, n=7-11, all p<0.05) associated with significant increases in HR (Peak HR: 114±9, 125±6 and 144±7 bpm). Atrial pacing (135, 150 and 165 bpm) also caused a frequency-dependent shortening of the QT interval (ΔQT: 15±3, 22±3, and 39±5 ms, n=6-7, all p<0.05). Regadenoson- and pacing-induced shortenings in the QT interval were significantly correlated with the R-R interval (r= 0.67 and 0.8, both p<0.05). Regadenoson at 5 and 10 μg/kg did not cause a significant change in HR or QT interval either during atrial pacing at 165 bpm or after administration of propranolol and atropine to prevent HR from changing, or after treatment of dogs with hexamethonium to block autonomic ganglia. Regadenoson (5-10 μg/kg) caused no significant changes of QT interval in the heart in which HR was kept constant via physiological or pharmacological procedures, indicating that regadenoson has no a direct effect on the QT interval.
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