急激な頭位変換時にのみ誘発される発作性房室ブロックの1例

A Case of Paroxysmal Atrioventricular Block Induced by Abrupt Change in Head Position

　症例は66歳男性．主訴は失神発作．安静時心電図は洞調律で，左軸偏位完全左脚ブロックを呈していた．理学所見，血液・生化学所見，心臓超音波検査，心筋シンチグラフィー，valsalva試験，頸動脈洞マッサージ，Head-up tilt test，頭部CT・MRI，聴覚・平衡覚検査では明らかな異常なし．発作性房室ブロックは非監視下で急激な頭位変換を施行した場合にのみ認め，同様の動作を監視下，あるいはゆっくり施行した場合には決して誘発されなかった．発作直前には，頻脈傾向なく，ブロック開始時に期外収縮も認めなかった．恒久型VDDペースメーカ植え込み後失神は全く認めない．機序として急激な頭位変換による副交感神経活動の亢進による第4相ブロックが考えられた．

　Paroxysmal atrioventricular (AV) block is an important cause of Adams-Stokes syndrome. We present a case of paroxysmal AV block induced merely by abrupt changes in the patient's head position. A 66-year-old man was admitted to our hospital for evaluation of long-standing, repetitive syncope. The 12-lead electrocardiogram showed complete left bundle branch block and a leftward axis, but auscultation of the chest, echocardiography, and 201-T1 scintigraphy yielded normal findings. Massage of the carotid sinus, valsalva test, and head-up tilt test disclosed no abnormality. Paroxysmal AV block was induced when the patient abruptly lay dawn on his back or bent his head, but did not provoke this reaction when he performed these actions under observation or at a low speed. The patient underwent the implantation of a VDD pacemaker, and has remained free of symptoms during a follow-up period of 2 years.