Antiarrhythmic efficacy of selective blockade of the cardiac slowly activating delayed rectifier current, I-Ks, in canine models of malignant ischemic ventricular arrhythmia

Background-To date, the lack of potent and selective inhibitors has hampere d the physiological assessment of modulation of the cardiac slowly activati ng delayed rectifier current, I-Ks. The present study, using the I-Ks block er L-768,673, represents the first in vivo assessment of the cardiac electr ophysiological and antiarrhythmic effects of selective I-Ks blockade. Methods and Results-In an anesthetized canine model of recent (8.5 +/- 0.4 days) anterior myocardial infarction, 0.003 to 0.03 mg/kg L-768,673 IV sign ificantly suppressed electrically induced ventricular tachyarrhythmias and reduced the incidence of lethal arrhythmias precipitated by acute, thrombot ically induced posterolateral myocardial ischemia, Antiarrhythmic protectio n afforded by L-768,673 was accompanied by modest 7% to 10% increases in no ninfarct zone ventricular effective refractory period, 3% to 5% increases i n infarct zone ventricular effective refractory period, and 4% to 6% increa ses in QTc interval, In a conscious canine model of healed (3 to 4 weeks) a nterior myocardial infarction, ventricular fibrillation was provoked by tra nsient occlusion of the left circumflex coronary artery during submaximal e xercise, Pretreatment with 0.03 mg/kg L-768,673 IV elicited a modest 7% inc rease in QTc,prevented ventricular fibrillation in 5 of 6 animals, and supp ressed arrhythmias in 2 additional animals. Conclusions-The present findings suggest that selective blockade of I-Ks ma y be a potentially useful intervention for the prevention of malignant isch emic ventricular arrhythmias.