Introduction: Is known that the QT interval duration depends on the heart rate (HR) and is related with the autonomic nervous system regulation. Patients with Long QT Syndrome (LQTS) due to mutation of the potassium channels have an abnormal response to abrupt changes in HR and to the sympathetic stimulation that occurs with the brisk standing. Electrocardiograms (ECGs) performed immediately after standing could be a diagnostic tool for this syndrome.
Objectives: To describe the presence of QT interval changes provoked by standing in patients with genetic confirmation of LQTS, and compare the results with a group of family members of patients with LQTS not carrying the familial mutation.
Methods: Results: LQTS patients had a mean age of 39 ± 18 years (mean±SD), and 40% were male. Among these, 8 (30%) had LQTS1, 16 (59%) LQTS2, and 3 (11%) LQTS7.In the control group the mean age was 42 ± 19 years, 50% males. QTc values in supine and in standing positions for both groups are shown in Table 1. Patients with LQTS mutations showed statistically significant differences between the mean QTc interval in supine and after brisk standing (p = 0.003 DII, P <0.001 V5). In contrast, the control group showed no differences (p = 0.928 DII, p = 0.432 V5). We also noted significant differences when compared the mean increase in the QTc interval between both groups (p = 0.001 DII, P = 0.015 V5). In the subgroup analysis, the increase in the mean QTc interval was 53 ± 51ms in DII and 31 ± 35ms in V5 for LQTS1; and 34 ± 34ms in DII and 29 ± 26ms in V5 for LQTS2, evidencing no significant differences between both subtypes of LQTS (p = 0,65).
Conclusions: Our population of patients with congenital LQTS had an abnormal QTc interval adaptation with the standing, showing a significant increase of this measure. Since our controls did not show this behavior, the performance of this test could be a useful tool in the diagnosis of individuals with baseline QTc interval at the upper limit of normal.