Unsuspected echocardiographic abnormality in the long QT syndrome. Diagnostic, prognostic, and pathogenetic implications.

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Abstract
BACKGROUND The idiopathic long QT syndrome (LQTS) is characterized by electrocardiographic abnormalities and by a high incidence of lethal arrhythmias. The present case/control study demonstrates the frequent occurrence of unusual and specific ventricular wall motion abnormalities in LQTS and their association with history of syncope or cardiac arrest. These anomalies were present in 23 of 42 LQTS patients (55%) and in two of 42 healthy controls (5%, p less than 0.0001) matched for age, sex, height, and weight. METHODS AND RESULTS Two new measurements were developed to assess quantitatively the abnormalities observed. The first, Th1/2, is an index of the rapidity of the early contraction phase; the second, TSTh, is an index of the presence of a slow movement in the late thickening phase. Th1/2 was smaller in LQTS patients (15.0 +/- 4.1 versus 19.9 +/- 3.9% of the cardiac cycle, p less than 0.001), indicating that they reach half-maximal systolic contraction more rapidly than controls. TSTh was greater in LQTS patients (9.37 +/- 6.82 versus 2.88 +/- 4.46%, p less than 0.001), indicating that they spend more time at a very low thickening rate. A peculiar double peak pattern of late thickening was present in 11 patients and in no controls. These abnormalities were more frequent in symptomatic than in asymptomatic patients (20 of 26, 77%, versus three of 16, 19%, p less than 0.005; relative risk, 2.75). They were not affected by beta-blockade or by left cardiac sympathetic denervation. The same echocardiographic abnormalities were produced by right stellectomy in nine of nine anesthetized dogs, were not dependent on cycle length, and were not modified by subsequent left stellectomy. CONCLUSIONS This study demonstrates a previously unsuspected abnormality in the ventricular contraction pattern of LQTS patients and, for the first time, provides evidence that a noninvasively detected cardiac abnormality is associated with a higher risk for syncope/cardiac arrest. The experimental reproduction of this echocardiographic abnormality by right stellectomy indicates that this newly found clinical characteristic of LQTS does not contradict the "sympathetic imbalance" hypothesis.