Anisotropy of steady speeds and delays of the extrasystolic waves in the heart of the dog

The authors have studied the spread of excitation in strips of the atria and ventricles of the myocardium of dogs. They demonstrate the anisotropy of the steady speeds and delays of the origin of the extrasystolic excitation. Along the fibres the speed is greater and the delay less than in the transverse direction. The degrees of anisotropy of the speeds and delays in each structure are approximately equal. The strongest anisotropy of the delays and speeds (~4·5) is in the muscular layer of the ventricle and the weakest (1·7) in the specialized layer. The anisotropies of the speeds and delays are greater the greater the anisotropy of the electrotonus. A new mechanism of the origin of extrasystolies (re-entry) in the system uniform in membrane properties but possessing anisotropy of the intercellular links is considered.