An expanded Methods section is available in the online Data Supplement .
Hearts of New Zealand White rabbits (n=45) were perfused with 37°C oxygenated normal Tyrode's solution. We simultaneously mapped Cai and Vm using Rhod-2 AM and RH237 on epicardial (n=14) or endocardial (n=14) surface of ventricles. In additional hearts, we mapped epicardial surfaces to explore the effect of IK1 suppression (n=8), and endocardial surfaces to study the effect of ryanodine (n=3) and IKr blocker, E-4031(n=2). Transmembrane potential (TMP) was recorded in an additional 4 rabbits. Cytochalasin D (10 μmol/L, n=7) or blebbistatin (10 to 20 μmol/L, n=15) or both (n=23) was used to inhibit contraction during optical and TMP recordings (online Supplement Figure I ).
Atrioventricular block was created in all hearts with cryoablation. VF was induced with burst ventricular pacing, and defibrillated with transvenous electrodes. To characterize spontaneous Cai elevation (SCaE), we performed ventricular pacing for 100 beats at a pacing cycle length (PCL) of 600, 500, 400, 300, 200 ms, and the minimum cycle length with 1:1 pacing capture. When substantial SCaEs emerged, pacing at the same PCL with different numbers of paced beats (50, 200, 300, and 400) were performed (n=6) to study a dependence of SCaE on the pacing duration. Isoproterenol at various concentrations (0.01 to 1.0 μmol/L) was administered, and defibrillation and pacing protocols were repeated. We defined the amplitude of baseline Vm and Cai transient as 1 arbitrary unit (AU). A focal ectopy with DAD at the earliest activation site (the onset of the optical action potential was required to precede the QRS onset of pseudo-ECG if it was available) was defined as TA.
Hearts of New Zealand White rabbits (n=45) were perfused with 37°C oxygenated normal Tyrode's solution. We simultaneously mapped Cai and Vm using Rhod-2 AM and RH237 on epicardial (n=14) or endocardial (n=14) surface of ventricles. In additional hearts, we mapped epicardial surfaces to explore the effect of IK1 suppression (n=8), and endocardial surfaces to study the effect of ryanodine (n=3) and IKr blocker, E-4031(n=2). Transmembrane potential (TMP) was recorded in an additional 4 rabbits. Cytochalasin D (10 μmol/L, n=7) or blebbistatin (10 to 20 μmol/L, n=15) or both (n=23) was used to inhibit contraction during optical and TMP recordings (
Atrioventricular block was created in all hearts with cryoablation. VF was induced with burst ventricular pacing, and defibrillated with transvenous electrodes. To characterize spontaneous Cai elevation (SCaE), we performed ventricular pacing for 100 beats at a pacing cycle length (PCL) of 600, 500, 400, 300, 200 ms, and the minimum cycle length with 1:1 pacing capture. When substantial SCaEs emerged, pacing at the same PCL with different numbers of paced beats (50, 200, 300, and 400) were performed (n=6) to study a dependence of SCaE on the pacing duration. Isoproterenol at various concentrations (0.01 to 1.0 μmol/L) was administered, and defibrillation and pacing protocols were repeated. We defined the amplitude of baseline Vm and Cai transient as 1 arbitrary unit (AU). A focal ectopy with DAD at the earliest activation site (the onset of the optical action potential was required to precede the QRS onset of pseudo-ECG if it was available) was defined as TA.
