交代性脚ブロックの出現機序に関する検討

Mechanism of alternating bundle branch block

　心室内変行伝導とは，短い連結期の上室性刺激が心室に達した際に，QRS波形の変化をきたす場合をいい，機能的脚ブロック^1,2）または第3相ブロック^3,4）とも呼ばれる。

　心房早期刺激法施行時に心室内変行伝導はしばしばみられる所見で，右脚ブロック型を示す場合が多い。しかし，まれに連結期の短縮により右脚（左脚）ブロック型の心室内変行伝導が出現し，さらに連結期を短縮させると左脚（右脚）ブロック型の心室内変行伝導が出現する交代性脚ブロックを経験することがある。

Atrial extrastimulus method was performed in 376 cases without bundle branch block and abnormal axis deviation. In eight of 376 cases, alternating bundle branch block appeared. Right bundle bran-ch block type of ventricular aberration occurred always in longer coupling interval than that of leftbundle branch block type of aberration. Remarka-ble propongation of H-V interval was found in left bundle branch block type of aberration. Five cases did not have splitting of His potential (type 1) and three cases had the splitting of its (type 2).

In type 1, difference between conduction time and refractory period of left and right bundle bran-ches or gap phenomenon (Damato's classification : Type II) could explain the occurrence of alternat-ing bundle branch block.

In type 2, the longitudinal dissociation in His bundle and gap phenomenon (Damato's classifica-tion : Type III) could explain the occurrence of alternating bundle branch block.