Therapeutic hypothermia (30 degrees C) enhances arrhythmogenic substrates, including spatially discordant alternans, and facilitates pacing-induced ventricular fibrillation in isolated rabbit hearts.
BACKGROUND
Therapeutic hypothermia (TH, 30 degrees C) protects the brain from hypoxic injury. However, TH may potentiate the occurrence of lethal ventricular fibrillation (VF), although the mechanism remains unclear. The present study explored the hypothesis that TH enhances wavebreaks during VF and S(1) pacing, facilitates pacing-induced spatially discordant alternans (SDA), and increases the vulnerability of pacing-induced VF.


RESULTS
Using an optical mapping system, epicardial activations of VF were studied in 7 Langendorff-perfused isolated rabbit hearts at baseline (37 degrees C), TH (30 degrees C), and rewarming (37 degrees C). Action potential duration (APD)/conduction velocity (CV) restitution and APD alternans (n=6 hearts) were determined by S(1) pacing at these 3 stages. During TH, there was a higher percentage of VF duration containing epicardial repetitive activities (spatiotemporal periodicity) (P<0.001). However, TH increased phase singularity number (wavebreaks) during VF (P<0.05) and S(1) pacing (P<0.05). TH resulted in earlier onset of APD alternans (P<0.001), which was predominantly SDA (P<0.05), and increased pacing-induced VF episodes (P<0.05). TH also decreased CV, shortened wavelength, and enhanced APD dispersion and the spatial heterogeneity of CV restitution.


CONCLUSIONS
TH (30 degrees C) increased the vulnerability of pacing-induced VF by (1)facilitating wavebreaks during VF and S(1) pacing, and (2)enhancing proarrhythmic electrophysiological parameters, including promoting earlier onset of APD alternans (predominantly SDA) during S(1) pacing.
Cardiovascular Center, Taichung Veterans General Hospital, Taichung and Department of Internal Medicine, Institute of Clinical Medicine, National Yang-Ming University School of Medicine, Taipei, Taiwan.
Yu-Cheng
YC
Hsieh
Shien-Fong
SF
Lin
Tung-Chao
TC
Lin
Chih-Tai
CT
Ting
Tsu-Juey
TJ
Wu
D000200:Action Potentials; D000818:Animals; D002304:Cardiac Pacing, Artificial / Q000009:adverse effects*; D004562:Electrocardiography / Q000379:methods; D005583:Fourier Analysis; D006329:Heart Conduction System / Q000503:physiopathology*; D007036:Hypothermia, Induced / Q000009:adverse effects*; D066298:In Vitro Techniques; D010477:Perfusion; D011817:Rabbits; D012815:Signal Processing, Computer-Assisted; D013997:Time Factors; D014693:Ventricular Fibrillation / Q000209:etiology* / Q000503:physiopathology; D056969:Voltage-Sensitive Dye Imaging