初回に有効性の確認された塩酸ニフェカラントの使用で著明なQT延長を伴う多形性心室頻拍を生じた心サルコイドーシスの1例

A Case of Cardiac Sarcoidosis Showing Variable Effects of Nifekalant Hydrochloride:Low dose of nifekalant hydrochloride induced QT prolongation and polymorphic ventricular tachycardia

　患者は心室頻拍と完全房室ブロックを合併した心サルコイドーシスの女性．無投薬状態での電気生理検査（EPS）では，早期刺激で単形性心室頻拍が繰り返し誘発された．塩酸ニフェカラントを通常量の50％用量（6.6mg静注）で導入した後，50％の維持量（8.8mg／hr），次いで80％用量（14.1mg／hr点滴静注）に増量すると，QT間隔は用量依存的に延長し，80％用量下では心室頻拍の誘発が不能となった．2回目のEPSにおいても右室心尖部からの単発早期刺激で同一の心室頻拍が誘発され，再度塩酸ニフェカラントを通常量の10％用量（1.3mg静注）で導入したところ，著明なQT間隔の延長（QT間隔500ms→750ms,QTc間隔602ms→823ms）とそれに引き続く多形性の非持続性心室頻拍が生じた．1回目の塩酸ニフェカラント使用時の心房心拍数が2回目より多く（107／分，87／分），交感神経活動が塩酸ニフェカラントのQT延長作用に何らかの修飾をもたらした可能性が考えられた．

This case was a 57-year-old woman having sustained monomorphic ventricular tachycardia (VT) associated with cardiac sarcoidosis. In the first study, nifekalant hydrochloride (NIF) was administrated with a loading dose of 0.15mg/kg followed by a maintenance dose of 0.2mg/kg/hr. Sustained VT came to be non-inducible concomitant with QT (QTc) interval prolongation from 500ms (666ms) to 520ms (684ms). Ten days later, a smal-ler dose of NIF was again administrated with a loading dose of 0.03mg/kg. However, the QT (QTc) interval unexpectedly prolonged from 500ms (602ms) to 700ms (823ms), and polymorphic non-sustained VT developed spontaneously. However basic heart rate and blood pressure were similar and electrocyte analysis was normal in both studies. Atrial rate in the first study was faster than in second study (107/min vs. 87/min). This suggests that a sympathetic situation might modify the QT prolongation by NIF. Magnitude of QT interval prolongation by NIF may vary in each situation, and we should pay attention to the QT interval in each treat-ment to prevent a possible proarrhythmic effect of the drug.