後天性QT 延長症候群の病態

The definition of long QT syndrome depends on demonstration of QT prolongation and recurrent syncope due to life-threatening ventricular arrhythmia . Acquired long QT syndromes are those due to drugs ( antiarrhythmic agents , antibiotics and phenothazines ), electrolyte abnormalities , acute ischemia and heart block. The ventricular arrhythmia is of a unique type known as torsade de pointes (TdP), which is characterized by rapid rates and gradually changing QRS morphology. Recently, It is reported that the cause of congenital long QT syndrome was abnormalities of gene coded myocardial ion channel, and some of acquired long QT syndrome was associated with congenital abnormalities of ion channel gene. In treatment of acquired long QT syndrome, the first step is to stop administration of the causative drug if can be identified. The aim of the therapy of TdP is to shorten and unify the uneven ventricular repolarization ; that is to correct the underlying electrophysiological disorder . Ventricular pacing and isoproterenol frequently prevent recurrent episodes of TdP by shortening action potential duration. Magnesuim is useful in treating TdP. The antiarrhythmic effect of magnesuim is due to shortening of the duration of ventricular vulnerable period during the cardiac cycle and prevention of ventricular arrhythmias related to reentry mechanism.

四国医学雑誌 : http://www.tokushima-u.ac.jp/med/research/shikoku_acta_medica.html