Submitted on August 27, 2007
Accepted on February 23, 2008
Moderate Hypothermia Increases the Chance of Spiral Wave Collision in Favor of Self-termination of Ventricular Tachycardia/Fibrillation
Masahide Harada1, Haruo Honjo2, Masatoshi Yamazaki1, Harumichi Nakagawa2, Yuko S. Ishiguro2, Yusuke Okuno1, Takashi Ashihara3, Ichiro Sakuma4, Kaichiro Kamiya2, and Itsuo Kodama1*
1 Department of Cardiovascular Research, RIEM Nagoya University, Nagoya, Japan
2 Nagoya, Japan; Department of Cardiovascular Research, RIEM Nagoya University, Nagoya, Japan
3 Department of Cardiovascular Medicine, Shiga University of Medical Science, Otsu, Japan
4 Graduate School of Engineering, The University of Tokyo, Tokyo, Japan
* To whom correspondence should be addressed. E-mail: ikodama{at}riem.nagoya-u.ac.jp.
In cardiac arrest due to ventricular fibrillation (VF), moderate hypothermia (MH, 33°C) has been shown to improve defibrillation success compared with normothermia (NR, 37°C) and severe hypothermia (SH, 30°C). The underlying mechanisms remain unclear. We hypothesized that MH might prevent reentrant excitations rotating around functional obstacles (rotors) which are responsible for the genesis of VF. In 2-dimensional Langendorff-perfused rabbit hearts prepared by cryoablation (n=13), action potential signals were recorded by a high-resolution optical mapping system. During basic stimulation (2.5-5.0Hz), MH and SH caused significant prolongation of action potential duration, and significant reduction of conduction velocity. Wavelength was unchanged at MH, whereas shortened significantly at SH at higher stimulation frequencies (4.0-5.0Hz). The duration of DC stimulation-induced VT/VFs was reduced dramatically at MH compared with NR and SH. The spiral wave (SW) excitations documented during VT at NR were by and large organized, whereas those during VT/VF at MH and SH were characterized by disorganization with frequent breakup. Phase maps during VT/VF at MH showed a higher incidence of SW collision (mutual annihilation or exit from the anatomical boundaries), which caused temporal disappearance of phase singularity points (PS-0), compared with NR and SH. There was an inverse relation between PS-0 period in the observation area and VT/VF duration. MH data points were located in longer PS-0 period and shorter VT/VF duration zone compared with SH. MH causes a modification of SW dynamics leading to an increase in the chance of SW collision in favor of self-termination of VT/VF.
