Comparative antifibrillatory effects of d- and dl-sotalol in normal and ischaemic ventricular muscle of the cat.

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 anaesthetized 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 ischaemia-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 anaesthetized cats is markedly increased by beta-adrenoceptor blockade and only marginally increased by the direct class III antiarrhythmic action of d-sotalol.