Objective The purpose of this study was to clarify the mechanism of 2:1 atrioventricular block (AVB) during AV node reentrant tachycardia (AVNRT) induced during electrophysioloic study.Methods In consecutive patients with AVNRT referred for electrophysiologic study, the data of 2 : 1 AVB during induced AVNRT was retrospectively analysed. Results The data of 4 patients was excluded from analyzing because of the unsatisfactory recording of His bundle potential during AVNRT. A His bundle deflection was present in the blocked beats in three of the remaining 5 patients and absent in the other two. At the beginning of AVNRT induced in those patients whose His bundle deflection was present in the blocked beats, H-V Wenckebach sequence with a QRS pattern of RBBB or LBBB was seen preceding and following the 2 : 1 AVB. A pattern of H-V Wenckebach phenomenon occurred once during AVNRT with 2:1 AVB in one of the two patients whose His bundle deflection was absent in the blocked beats.Conclusion The induced 2:1 AVB during AVNRT is due to functional block in the His-Purkinje system regardless of the presence or absence of a His bundle deflection in blocked beats.

Objective To study the effect of light intensity and light quality on the growth and total flavonoid accumulation of Erigeron breviscapus. Methods Young plants of E. breviscapus were planted under various color films and light intensities, their biomass and total flavonoid content were determined when plants flowered. Results The biomass and total flavonoid content of individuals under 100% and 80% sunshine were higher than those under 50% sunshine. The biomasses of plants under yellow, red, purple, or blue film were lower than those under white film. Under the blue film, the total flavonoid content of the plant was the highest; while under white film, the total flavonoid yield was the highest. Conclusion Light intensity and light quality significantly affect the growth and total flavonoid accummulation of E. breviscapus. The biomass and total flavonoid yield are the highest when under full sunshine.