Comparative Antifibrillatory Effects of d- and dl-Sotalol in Normal and Ischaemic Ventricular Muscle of the Cat

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Abstract
The aim of this study was to compare the effects of d- and dl-sotalol on the ventricular fibrillation threshold (VFT) and the effective refractory period (VERP) in anaesthetised cats subjected to coronary artery occlusion. Occlusion of the left anterior descending coronary artery caused a decrease in VFT (measured in mA) (1.40 .+-. 0.1 to 0.6 .+-. 0.1). dl-Sotalol (1 and 5 mg kg-1) increased VFT before the induction of ischaemia (1.7 .+-. 0.1 to 33.8 .+-. 1.0 and 38, respectively), and the higher dose prevented the ishaemia-induced fall in VFT. d-Sotalol (1 and 5 mg/kg-1) caused only small increases in VFT in normal (1.9 .+-. 0.3 to 2.3 .+-. 0.3 and 2.6 .+-. 0.3) and ischaemic (0.8 .+-. 0.1 to 1.2 .+-. 0.2 and 1.3 .+-. 0.2) myocardium. Both d- and dl-sotalol increased VERP measured in normal myocardium. The % changes observed with 1 and 5 mg kg-1 of the racemate (17 .+-. 1 and 57 .+-. 4) were significantly greater than those with the d-isomer (8 .+-. 3 and 16 .+-. 2). dl-Sotalol, but not d-sotalol, prevented the haemodynamic responses to 50 ng kg-1 isoprenaline. These results suggest that VFT in anaesthetised cats is markedly increased by .beta.-adrenoceptor blockade and only marginally increased by the direct class III antiarrhythmic action of d-sotalol.