Changing QT interval in orthostasis — new diagnostic marker of syndrome of extended QT interval

Abstract

Long QT interval syndrome (LQTS) is a disease that causes life-threatening arrhythmias and sudden death syndrome. Recently, it has been shown that about half of patients with LQTS have normal QTc interval values on an ECG. The purpose of this study was to assess changes in the QT interval in patients with LQTS in orthostasis to identify additional criteria for the disease. Surveyed 64 patients from 4 to 47 years old (13.3 ± 10.0) with LQTIS. The control group consisted of 87 healthy people of 4–20 years (11.0 ± 3.5). An ECG was performed in a lying and standing position. HR, QT and QTc interrvals in both positions and the difference between these indicators were evaluated. In both groups, we noted an increase in heart rate and QTc and a shortening of the QT interval in orthostasis. Distinctions between all parameters were revealed reliably, except for the increase in the QTc interval (∆QTc) in the main and control groups. ROC analysis revealed that the optimal point for identifying patients with LQTS is QTc interval in orthostasis –500 ms with Se 73 % and Sp 93 %. Conclusions. In the early period of orthostasis, an increase in the heart rate, a shortening of the QT interval and a prolongation of the QTc interval occur; lengthening the QTc interval in the early period of orthostasis over 500 ms is highly sensitive and highly specific in identifying patients with the syndrome of prolonged QT-interval.