植込み型除細動器が感知しなかった心室頻拍による突然死ニアミス

Near-miss Sudden Arrhythmic Death caused by Ventricular Tachycardia that was not detected by the Implantable Cardioverter Defibrillator

要旨　植込み型除細動器(ICD)は心室頻拍/心室細動(VT/VF)による心臓突然死(SCD)予防に最も優れている．しかし，その治療設定に苦慮する症例も少なくない．われわれは，自然発作などで予測した心室不整脈(VA)周期以下のVAのためのICD非作動によるSCDニアミスを経験した．患者は69歳，男性．陳旧性心筋梗塞(駆出率15%)に伴うVTから意識消失発作の既往があり，ICDとアミオダロン200mg/日で治療を行っていた．ICD植込み5カ月後に２度VT(心拍数210bpm)がみられているが，いずれもICDによる治療に成功した．その後，非持続性VT増加のため入院し，アミオダロンが300mg/日に増量された．しかし，増量後9日目にSCDニアミスを起こした．心電図モニター上は持続性VAが記録されていたが，その心拍数はそれまでに確認されていたVTよりも明らかに低下しており(心拍数150bpm)，ICDの設定を下回り治療が行われなかった．院内発症であったため蘇生が可能であった．

Summary

Implantation of cardioverter defibrillators(ICDs) is the most useful method for the prevention of sudden cardiac death(SCD), but the adjustment of the algorism for optimal treatment is not always easy. We encountered a case who experienced a near-miss SCD due to a ventricular arrhythmia(VA) with a longer cycle length than the tachycardia detection interval(TDI). The case was that of a 69 year-old male with poor cardiac function(ejection fraction of the left ventricle was only 15%) caused by a previous myocardial infarction and who had a history of near-miss SCD. For this reason, an ICD and the administration of amiodaron(200mg/day) were prescribed. Five months after the implantation, two discharges were successful in terminating two VA episodes. However, because repeated non-sustained VAs took place, amiodaron was augmented to 300mg/day. Nine days later, near-miss SCD occurred due to a failure in detection by the ICD. The electrocardiograms revealed a VA with a lower late(150 bpm) than the TDI. The patient survived because the event occurred in the hospital. Catheter ablation of the VAs induced in the electrophysiological study using the pace-mapping method was helpful in this patient.