心房早期刺激中に機能的交代性脚ブロックの出現をみた1症例

A case with functional alternating bundle branch block induced by premature atrial stimulation

　電気生理学的検索において，心房早期刺激時や心房ペーシング時ヒス・プルキニエ系に交代性ブロックを含む脚ブロックや伝導遅延の出現することが報告されており^1〜4），しかもそれらが正常の心室内伝導を有する患者にも観察されている^3）。さらにそのようなブロックの出現が心拍依存性を示す例の電気生理学的検索も報告されている^1,5）。

　今回我々は上室性頻拍症を主訴とする患者における電気生理学的検索中，安静コントロール時正常のA-H間隔，H-V間隔を示したが，心房早期刺激時に機能的交代性脚ブロックの出現をみ，しかも基本刺激周期に依存性を示す症例を経験したので電気生理学的考察を加え報告する。

The patient was a 60 years old woman with episodes of supraventricular tachycardia. Her ECG was normal at rest. Electrophysiological studies revealed normal A-V conduction; A-H interval of 70 msec and H-V interval of 40 msec. With a basic cycle length of 667 msec, premature atrial stimuli induced functional alternating bundle branch block. (BBB). At A₁-A₂ intervals of 400 msec or more, H₁-H₂ intervals were longer than 420 msec, and H₂s were conducted to the ventricle with a normal QRS configuration. At A₁-A₂ intervals of 370-320 msec with corresponding H₁-H₂ intervalsof 395-385 msec, Hs₂ were conducted with a pattern of right BBB, but the H₂-V₂ interval were almost unchanged. At A₁-A₂ intervals of 315 and 310 msec with corresponding H₁-H₂ intervals of 370 and 380 msec, H₂s were propagated to the ventricle with left BBB configuration and marked prolongation of the H₂-V₂ intervals were found. At A₁-A₂ intervals of 300 msec or less, the corresponding H₁-H₂ intervals were 315 msec or more and H₂s were again conducted to the ventricle with normal QRS pattern. With more rapid basic cycle length, i.e. S₁S₁=500 and 400 msec, such alternating BBB were not induced, and intranodal reentrant tachycardia were induced at the critical A₁-A₂ intervals. The developmnt of functional alternating BBB depend on the basic cycle length and it developed at the critical H₁-H₂ interval. It seems that alternative BBB also develop in patients with normal A-V conduction.