Handgrip strength test for the diagnosis of long QT syndrome

Abstract

Long QT syndrome (LQTS) assessment is based on the QT/ÖRR equation (the so-called Bazett's formula) and calculating the corrected QT (QTc). However, this formula reliably estimates the QT interval in the heart rate range (HR) of 60-90 bpm, which makes it difficult to diagnose LQTS in patients with sinus bradycardia, typical of this disease.Aim. To improve the LQTS diagnosis in patients with sinus bradycardia using the handgrip strength test.Material and methods. A total of 188 patients aged 5-53 years (16 [13;17]) were examined: group I — 40 healthy children aged 9-17 years (14 [12;16]); group II — 98 athletes with sinus bradycardia <60 bpm aged 16 [16;17] years; group III — 50 patients with LQTS aged 5-53 years (12 [10;16]). The handgrip strength test consisted of regular rhythmic compression of a hand expander with a resistance of 20 kg until the heart rate increased >60 bpm. The patients had an electrocardiogram recorded twice before and after the handgrip test. Heart rate, QT and QTc intervals were analyzed.Results. In all groups, after using the expander, there was a significant increase in heart rate, QT interval shortening and QTc interval prolongation. QTc interval prolongation after the handgrip test >460 ms was a highly sensitive marker of LQTS (Se 96%, Sp 60%).Conclusion. Proposed handgrip test for sinus bradycardia makes it possible to increase heart rate, which ensures a more correct use of the Bazett's formula for assessing the corrected QT interval (QTc). QTc interval prolongation over 460 ms after the handgrip test is a highly sensitive additional marker for identifying patients with LQTS.