Mouse intracardiac ECG recordings

Intracardiac atrial, atrioventricular nodal, and ventricular electrograms were recorded simultaneously in anesthetized RyR2-WT and mutant mice using a 1.1-F octa-polar catheter (EPR-800, Millar Instruments, Houston, TX). To induce VAs, an LBLPS pacing protocol with a long burst (20 beats at a 60-ms cycle length) followed by a long-coupled ventricular extra-stimulus (122 ms) and a subsequent short-coupled extra-stimulus was used. The short-coupled interval was progressively reduced from 78 to 18 ms in 4-ms steps. VA was defined as four or more ventricular ectopic beats after pacing, VA inducibility (%) as the proportion of animals that developed VAs per group, average VA duration as the summed duration of VA/total VA episodes for each group, and VA incidence (%) as the total number of VA episodes/total numbers of pacing trials for each group.