4種類のgap現象を認めた大動脈弁狭窄症の1例

A case of aortic stenosis with four types of gap phenomenon in A-V conduction

　房室伝導におけるgap現象は，房室伝導系各部位における不応期に相違があるために出現し，順伝導および逆伝導におけるいくつかの型があることが報告されている^1〜4）。

　基本周期の変化は，伝導系各部の不応期の変化をもたらすが，その程度に差があるため，基本周期の変化によりgap現象が出現，消失もしくは他の型のgap現象へ変化することがある。

Electrophysiological study was performed in a 57-year-old patient with aortic stenosis for evaluation of sinus bradycardia. Atrial extra-stimulus methods were performed during sinus rhythm and with atrial pacing at cycle length of 900msec and 750 msec.

During sinus rhythm, A₂ was not conducted to the ventricle (H-V block) at A₁-A₂ intervals of 405 msec to 380 msec. At A₁-A₂ interval between 375 msec and 320 msec, the H₂-V₂ interval prolonged remarkably and conduction resumed to the ventricle (type 2 gap phenomenon). At A₁-A₂ interval between 315 msec and 310 msec (HRA₁-HRA₂ interval: 305 msec.~295 msec), H-V block occurred again. When the HRA₁-HRA₂ interval was reduced to 290 msec, resumption of conduc-tion to the ventricle occurred because of intra-atrial conduction delay (type 5 gap phenomenon).

During atrial pacing at cycle length of 900 msec, type 2 and type 1 gap phenomenon occurred and at cycle length of 750 msec, type 4 gap phenomenon occurred. The conduction delay occurred within the slow pathway of the A-V node in type 1 and type 4 gap phenomenon.

The occurrence of these gap phenomenon was con-sidered due to the existence of the dual A-V nodal pathways and conduction disturbance in the His-Purk-inje system.