Objectives To understand the function of the repolarisation reserve provided by slowly activated delayed rectifier potassium current (I_Ks) in the prevention of ventricular arrhythmias during cardiac ischemia/reperfusion.

Methods The responses of monophasic action potential duration (MAPD) prolongation and triangulation were investigated following an L-768, 673-induced blockade of I_Ks (L-768, 673 or vehicle) with or without ischemia/reperfusion (IR or Sham) in a rabbit model of left circumflex coronary artery occlusion/reperfusion.

Results MAPD90 and MAPD60 of Group IR+L-768,673 were significantly prolonged during reperfusion and Triangulations of Group IR+L-768, 673 were increased by 31.1%, 26.5%, 19.3% at the time point of reperfusion 45 min, 60 min and 75 min respectively, when compared with those of Group IR+vehicle. Within this period, the median number of premature ventricular beats increased by 4.6-fold in comparison with that of Group IR+vehicle (p<0.05) and a higher ventricular tachycardia incidence was detected in Group IR+vehicle than IR+vehicle (4/8 vs 1/8, p>0.05).

Conclusion Blockade of I_Ks caused MAP triangulation, which precipitated ventricular arrhythmias.