[Dependence of ventricular wallstress-induced refractoriness changes on pacing cycle lengths and its mechanism].

The aim of this article was to investigate the dependence of ventricular wallstress-induced refractoriness changes on pacing cycle lengths and its mechanism in anaesthetized rabbits. The rabbit heart preparation was used. The left ventricular afterload was increased by partially clipping the root of the ascending aorta. The changes in effective refractory periods (ERP) induced by the left ventricular afterload rising were examined at different pacing cycle lengths (1000, 500, 300 and 200 ms). In addition, the effect of streptomycin on these changes was also observed. The results are as follows: (1) The rising of left ventricular afterload led to marked changes in ERP at rapidly pacing cycle lengths (300 ms, 21+/-5 ms, 17.0%; 200 ms, 19+/-3 ms, 18.8%. P<0.01) than at slow ones (1000 ms, 3+/-2 ms, 1.5%; 500 ms, 7+/-3 ms, 4.0%. P>0.05); (2) Streptomycin inhibited the changes caused by the left ventricular afterload rising at pacing cycle lengths 300 ms and 200 ms (P>0.05). It is suggested that ventricular wallstress-induced refractoriness changes are pacing cycle length-dependent, and the effect of streptomycin appears to be consistent with the inhibition of stretch-activated ion channels.