Value of the "Standing Test" in the Diagnosis and Evaluation of Beta-blocker Therapy Response in Long QT Syndrome

Introduction and objectives: Patients with congenital long QT syndrome (LQTS) have an abnormal QT adaptation to sudden changes in heart rate provoked by standing. The present study sought to evaluate the standing test in a cohort of LQTS patients and to assess if this QT maladaptation phenomenon is ameliorated by beta-blocker therapy.

Methods: Electrographic assessments were performed at baseline and immediately after standing in 36 LQTS patients (6 LQT1 [17%], 20 LQT2 [56%], 3 LQT7 [8%], 7 unidentified-genotype patients [19%]) and 41 controls. The corrected QT interval (QTc) was measured at baseline (QTc_supine) and immediately after standing (QTc_standing); the QTc change from baseline (ΔQTc) was calculated as QTc_standing - QTc_supine. The test was repeated in 26 patients receiving beta-blocker therapy.

Results: Both QTc_standing and ΔQTc were significantly higher in the LQTS group than in controls (QTc_standing, 528 ± 46ms vs 420 ± 15ms, P < .0001; ΔQTc, 78 ± 40ms vs 8 ± 13ms, P < .0001). No significant differences were noted between LQT1 and LQT2 patients. Typical ST-T wave patterns appeared after standing in LQTS patients. Receiver operating characteristic curves of QTc_standing and ΔQTc showed a significant increase in diagnostic value compared with the QTc_supine (area under the curve for both, 0.99 vs 0.85; P < .001). Beta-blockers attenuated the response to standing in LQTS patients (QTc_standing, 440 ± 32ms, P < .0001; ΔQTc, 14 ± 16ms, P < .0001).

Conclusions: Evaluation of the QTc after the simple maneuver of standing shows a high diagnostic performance and could be important for monitoring the effects of beta-blocker therapy in LQTS patients.