Abstract
Long QT syndrome (LQTS) is hereditary disease caused by dysfunction of ion channels. Patients suffer from increased risk of polymorphic ventricular tacycardia or ventricular fibrilation, mainly during adrenergic stimulation.
Estimated prevalence is up to 1 : 2500. About 15–20% of sudden cardiac death in people of age less than 40 can be attributed to LQTS.
One of the goals of preparticipation examination is screening of LQTS for which the QT interval measurement is crucial part. Currently, proposal for cut-off value increased to 470 ms in men and 480 ms in women.
On one hand, it can increase positive predictive value and decrease number of false positives, but on the other hand it also increases number of (true) negative measurements. We don’t need to know the exact corrected QT interval (QTc) value in this cohort of athletes.
It is sufficient to know for sure, that the QTc is not prolonged. This was the aim of development of a completely new ECG ruler for graphic screening of QT interval prolongation.
The main principle of the ruler is to graphically find QT interval length corresponding to selected cut-off value (currently 430 ms) with conjunction with given RR interval. It is a sort of reverse correction of QTc.
The ruler can be used with ECG curves with 50 mm/s speed and in the range of heart rate of 50–120/min, correction is after Bazett. Detailed step by step instructions for use are enclosed.
The ruler is not meant to replace standard manual QTc measurement which we have to use in case of QTc prolongation suspicion, it is rather a complementary tool.