N-acetyl procainamideにより誘発されたTorsade de Pointesの1例

A case of Torsade de Pointes induced by N-acetyl procainamide

　Torsade de Pointes（TdP）は，1966年フランスのDessertenne^1）が命名した突然起こる心拍数150回／分以上で，心電図上QRS軸が基線に対してねじれる（twist）ようにみえる特異な心室頻拍である。

　最近我々は，Procainamide（PA）の代謝産物であるN-acetyl procainamide（NAPA）が原因でTdPを生じた1例を経験したので若干の考察を加えて報告する。

The patient was a 57-year-old man with chronic renal failure due to amyloidosis.

He was admitted to the hospital for hemodialysis. As the patient had frequent episodes of short runs ofventricular tachycardia, procainamide (PA) (1.0g/day) was started. On 24th days after PA administration, he experienced frequent episodes of Torsade de Pointes (TdP) during hemodialysis.

Blood concentrations of PA and N-acetyl procainamide (NAPA), which is a major metabolic product of PA, were 4.6μg/ml and 41.5μg/ml respectively. The former was in the therapeutic level but the latter was in the toxic one.

QT interval (0.66 second) and QTc (0.68 second) were both markedly prolonged. PA was discontinued and lidocaine was started.

About 20 days later, blood concentration of PA and NAPA were decreased to 0μg/ml and 0.4μg/ml respe-ctively. At that time, QT interval and QTc were normalized.

The cause of TdP was considered to be the accumula-tion of NAPA due to chronic renal failure.

Prompt cessation of PA and lidocaine therapy were effective in this case.