Moderate Hypothermia (33 C) Decreases the Susceptibility to Pacing-Induced Ventricular Fibrillation Compared with Severe Hypothermia (30 C) by Attenuating Spatially Discordant Alternans in Isolated Rabbit Hearts

Background: Severe hypothermia (SH, 30 C) increases the risk of pacing-induced ventricular fibrillation (PIVF) by enhancing spatially discordant alternans (SDA). Whether moderate hypothermia (MH, 33 C), which is clinically used for therapeutic hypothermia, also facilitates SDA remains unclear.We hypothesized thatMH attenuates SDA occurrence compared with that achieved by SH, and decreases the susceptibility of PIVF. Methods: Using an optical mapping system, action potential duration (APD)/conduction velocity restitutions and thresholds of APD alternans were determined by S1 pacing in Langendorff-perfused isolated rabbit hearts. In the MHgroup (n = 7), S1 pacing was performed at baseline (37 C), after 5-minMH, and after 5-min rewarming (37 C). In the SH group (n = 9), pacing was also performed at baseline (37 C), after 5-min SH, and after 5-min rewarming (37 C). The thresholds of APD alternans were defined as the longest S1 pacing cycle length at which APD alternans were detected. Results: Although the thresho