Changes in ventricular refractoriness and conduction velocity induced by local hypothermia and hyperthermia

VF pattern is related to the electrophysiological parameters of the myocardium. Although the influence of global temperature on these parameters is known, the effects of its regional variations have not been sufficiently studied. We examined the effects of local hypothermia and hyperthermia on refractoriness and conduction velocity (VC), during constant pacing at cycle lengths of 250 ms. In an experimental model (rabbit isolated heart) we used a new method to perform epicardial cooling and heating on the registered surface. The results show that local variations of temperature generate heterogeneity in the electrophysiological properties of the heart. Hypothermia prolongs refractoriness and decreases VC, in a reversible manner. Hyperthermia (42degC) has the opposite effects. The wavelength of the cardiac impulse is not altered because of the opposite and proportional actions on functional refractory period and VC