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 that MH 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 MH group (n = 7), S1 pacing was performed at baseline (37 °C), after 5-min MH, 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 thresholds of APD alternans were not different between the MH (273 ± 46 ms) and the SH (300 ± 35 ms) (p = 0.281) groups, SDA threshold was shorter (at a faster heart rate) during MH (228 ± 33 ms) than that during SH (289 ± 42 ms) (p = 0.028). At APD alternans threshold, SH hearts showed more SDA than that during MH (SH: 7 hearts, MH: 2 hearts, p = 0.049). SDA could be induced in all 9 SH hearts (100%), while only 4 MH hearts (57%) had SDA (p = 0.029). The PIVF inducibility during SH (44 ± 53%) was higher than that during MH (0%) (p = 0.043).


CONCLUSIONS
Compared with SH, the MH group showed greater attenuation of SDA and decreased the susceptibility of PIVF. Therefore, MH is safer as a procedural guideline for use in clinical therapeutic hypothermia than SH.


BACKGROUND
Cardiac alternans; Conduction velocity; Hypothermia; Optical mapping.
Cardiovascular Center, Taichung Veterans General Hospital, Taichung, and Department of Internal Medicine, Faculty of Medicine, Institute of Clinical Medicine, Cardiovascular Research Center, National Yang-Ming University School of Medicine, Taipei; ; Department of Financial and Computational Mathematics, Providence University, Taichung, Taiwan;
Yu-Cheng
YC
Hsieh
Krannert Institute of Cardiology and the Division of Cardiology, Department of Medicine, Indiana University School of Medicine, Indianapolis, IN; ; Institute of Biomedical Engineering, National Chiao Tung University, Hsinchu, Taiwan.
Shien-Fong
SF
Lin
Cardiovascular Center, Taichung Veterans General Hospital, Taichung, and Department of Internal Medicine, Faculty of Medicine, Institute of Clinical Medicine, Cardiovascular Research Center, National Yang-Ming University School of Medicine, Taipei;
Jin-Long
JL
Huang
Cardiovascular Center, Taichung Veterans General Hospital, Taichung, and Department of Internal Medicine, Faculty of Medicine, Institute of Clinical Medicine, Cardiovascular Research Center, National Yang-Ming University School of Medicine, Taipei;
Chen-Ying
CY
Hung
Cardiovascular Center, Taichung Veterans General Hospital, Taichung, and Department of Internal Medicine, Faculty of Medicine, Institute of Clinical Medicine, Cardiovascular Research Center, National Yang-Ming University School of Medicine, Taipei;
Jiunn-Cherng
JC
Lin
Cardiovascular Center, Taichung Veterans General Hospital, Taichung, and Department of Internal Medicine, Faculty of Medicine, Institute of Clinical Medicine, Cardiovascular Research Center, National Yang-Ming University School of Medicine, Taipei;
Ying-Chieh
YC
Liao
Department of Financial and Computational Mathematics, Providence University, Taichung, Taiwan;
Chu-Pin
CP
Lo
Cardiovascular Center, Taichung Veterans General Hospital, Taichung, and Department of Internal Medicine, Faculty of Medicine, Institute of Clinical Medicine, Cardiovascular Research Center, National Yang-Ming University School of Medicine, Taipei;
Kuo-Yang
KY
Wang
Cardiovascular Center, Taichung Veterans General Hospital, Taichung, and Department of Internal Medicine, Faculty of Medicine, Institute of Clinical Medicine, Cardiovascular Research Center, National Yang-Ming University School of Medicine, Taipei;
Tsu-Juey
TJ
Wu