what is considered qt prolongation
QT Prolongation. Recognition of a prolonged QT interval is complicated by the problems inherent in identification of T wave end and the inaccuracy of Bazlet's formula for correcting for heart rate. It may be preferable to judge the QT interval by changes in length or when it exceeds 50% of the R-R interval.T prolongation can be due to rare hereditary abnormalities, to type Ia anti-arrhythmics such as quinidine, and to hypocalcemia or hypomagnesia. The importance of recognizing prolonged QT interval is that it is associated with PVC's, ventricular tachycardia and fibrillation (ie., vulnerability to lethal arrhythmia).