Circulation, Vol 84, 1530-1542, Copyright © 1991 by American Heart Association
F Nador, G Beria, GM De Ferrari, M Stramba-Badiale, EH Locati, A Lotto and PJ Schwartz
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.
ARTICLES
Unsuspected echocardiographic abnormality in the long QT syndrome. Diagnostic, prognostic, and pathogenetic implications
Dipartimento di Medicina, Universita di Pavia, Italy.
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