Increased susceptibility of the heart to arrhythmia in response to QT-prolongation associated with unhomogeneous repolarization: further data concerning the pathomechanism of arrhythmias associated with long QT-syndrome.

The pathomechanism of arrhythmias consecutive to a prolonged electrical systole --the long QT syndrome--was studied by local hypothermia in the heart. Local increase in the QT-interval (long QT with unhomogeneous repolarisation) was induced at a circumscribed area of the right ventricle by perfusion of the mid- and end-sections of the right coronary with cooled blood. The effect of local prolongation of QT on the arrhythmic susceptibility of the heart was studied by means of programmed electrical stimulation. Induced local hypothermia of the heart was found to increase the QT-interval of the ECG-tracings, also if QT had been corrected for heart rate. The local ECG tracings showed a considerable increase of the QT-interval at the selected right ventricular area under the effect of induced hypothermia but in relation to QT (ERP/QT) it diminished. The long QT in association with an unhomogeneous repolarization went hand in hand with an increased irritability of the heart. Early ventricular impulses were found to elicit extrasystolic runs, ventricular tachycardia or ventricular fibrillation. The results indicate that the cause of tachyarrhythmias consecutive to the long QT-syndrome may be ascribed to the inhomogeneity of repolarization on the one hand, and to the shortness of ERP in relation to the QT-duration on the other.