Role of Apamin-Sensitive Calcium-Activated Small-Conductance Potassium Currents on the Mechanisms of Ventricular Fibrillation in Pacing-Induced Failing Rabbit Hearts

Background-Ventricular fibrillation (VF) during heart failure is characterized by stable reentrant spiral waves (rotors). Apamin-sensitive small-conductance calcium-activated potassium currents (I-KAS) are heterogeneously upregulated in failing hearts. We hypothesized that I-KAS influences the location and stability of rotors during VF. Methods and Results-Optical mapping was performed on 9 rabbit hearts with pacing-induced heart failure. The epicardial right ventricular and left ventricular surfaces were simultaneously mapped in a Langendorff preparation. At baseline and after apamin (100 nmol/L) infusion, the action potential duration (APD(80)) was determined, and VF was induced. Areas with a >50% increase in the maximum action potential duration (Delta APD) after apamin infusion were considered to have a high I-KAS distribution. At baseline, the distribution density of phase singularities during VF in high I-KAS distribution areas was higher than in other areas (0.0035 +/- 0.0011 versus 0.0014 +/- 0.0010 phase singularities/pixel; P=0.004). In addition, high dominant frequencies also colocalized to high I-KAS distribution areas (26.0 versus 17.9 Hz; P=0.003). These correlations were eliminated during VF after apamin infusion, as the number of phase singularities (17.2 versus 11.0; P=0.009) and dominant frequencies (22.1 versus 16.2 Hz; P=0.022) were all significantly decreased. In addition, reentrant spiral waves became unstable after apamin infusion, and the duration of VF decreased. Conclusions-The I-KAS current influences the mechanism of VF in failing hearts as phase singularities, high dominant frequencies, and reentrant spiral waves all correlated to areas of high I-KAS. Apamin eliminated this relationship and reduced VF vulnerability.