Abstract 2480: Abnormal Physiology of QT Adaptation in Short QT Syndrome: Impact for Diagnosis
Short QT syndrome (SQTS) is a malignant disease with remarkable risk of sudden cardiac death. Albeit crucial for clinical management, the diagnosis is often difficult for the lack of standards to measure QT duration. We aimed at assessing the dynamic of QT interval in SQTS (n=12) patients (QTc ≤350ms) and healthy subjects (CTRL n=12). All subjects underwent Holter recordings (HOL) and exercise stress test (StT). We determined at least one QT measure in lead II for each hour at different RR intervals during HOL. QT and RR intervals were also assessed at rest and at the peak exercise. During HOL, QT was shorter in SQTS than in CTRL but the difference between QTc intervals became progressively less evident with heart rate increase (delta: 42±19ms vs. 22±19ms, p<0.05 RR range: 700–1100ms -Figure⇓). Furthermore, QT (at 60bpm) during sleep increased significantly vs. daytime in SQTS (343±12ms, vs. 318±12ms p<0.001) while no difference was found in CTRL (398±9ms vs. 396±16ms, p=ns). Different QT/RR relationship was observed during StT: QT interval shortening was less marked in SQTS vs. CTRL: 75±19ms vs. 138±23 p<0.001 despite similar RR change (delta RR 492±114ms vs. 534±73ms; p=ns) and QT/RR slope was lower (0.14 vs. 0.36; p<0.001) indicating impaired QT adaptation in SQTS. In summary our data show significant abnormalities of QT dynamics in SQTS that may impair the diagnostic sensitivity by increasing the overlap between healthy subjects and SQTS in some instances. The evidence of impaired adaptation to sudden heart rate changes but increased day-night differences suggest that correct SQTS diagnosis should be made on ECG recordings at rest, during daytime at a rate range between 60 and 80 bpm.