Effect of calcium channel block on the wall motion abnormality of the idiopathic long QT syndrome

Background: We recently showed the frequent occurrence of an unusual ventricular wall motion abnormality, assessed by echocardiography, in patients with the idiopathic long QT syndrome (LQTS). Two new quantitative indexes were developed: Th( 1/2 ) (time needed to reach half of the maximal systolic thickening), which was smaller in LQTS patients than in controls; and TSTh (time spent at a very low thickening rate before rapid relaxation), which was much greater in LQTS patients, indicating the presence of a slow contraction in the late thickening phase. This marked late systolic 'plateau,' either rectilinear or with a peculiar double peak pattern, was significantly more frequent in patients with a history of syncope or cardiac arrest. The mechanism underlying this puzzling phenomenon remained unexplained. Methods and Results: The present study assessed the effects of the calcium channel blocker verapamil on the contraction pattern in 10 LQTS patients (9 females and 1 male; mean age, 19±7 years) with a marked plateau pattern and in 6 healthy controls (4 females and 2 males; mean age, 28 ± 5 years). Either verapamil (0.1 mg/kg) or saline was randomly injected over 2 minutes. Saline had no effect. In LQTS patients, verapamil increased Th( 1/2 ) by 27%, from 16.9±3.2% to 21.4±3.9% of the cardiac cycle (P=.005), and dramatically reduced TSTh by 92%, from 13.7 ± 5.3% to 1.08±0.6% of the cardiac cycle (P