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Medline ® Abstract for Reference 102

of 'Acquired long QT syndrome'

Torsades de pointes associated with acquired long QT syndrome: observation of 7 cases.
Takahashi N, Ito M, Inoue T, Koumatsu K, Takeshita Y, Tsumabuki S, Tamura M, Inoue K, Maeda T, Saikawa T
J Cardiol. 1993;23(1):99.
We examined the clinical characteristics and electrocardiographic findings of 7 patients having the acquired long QT syndrome who developed torsades de pointes while receiving no antiarrhythmic drugs. A total of 43 episodes of torsades de pointes were documented among these patients. Underlying heart diseases were present in 6 patients and hypopotassemia (<or = 3.3 mEq/l) in 4. Four had bradycardia (<or = 52 beats/min) immediately before the development of torsades de pointes. The QTc intervals measured immediately before the episodes of torsades de pointes were significantly longer than those 6-24 hours before the episodes (0.69 +/- 0.10 vs 0.56 +/- 0.10 sec, p<0.05), while heart rates did not differ significantly between these 2 periods (54 +/- 12 vs 58 +/- 15 beats/min). The ventricular rate of torsades de pointes was 192 +/- 24 beats/min. A "long-short initiating cycle" was noted in all 43 episodes, and the initiating premature ventricular beat (PVB) showed the "R on T(U)" phenomenon in 42 of the episodes. A notched T-U complex due to a prominent slow wave (U wave) at the end of the T wave was noted in 5 patients immediately before the episodes of torsades de pointes. Prolongation of the preceding RR interval was directly related to the increase of the U wave amplitude, which caused an increased likelihood of the occurrence of PVBs near the peak of the U wave. Torsades de pointes developed from the largest U wave. Direct current cardioversion was transiently effective for treating torsades de pointes, and intravenous lidocaine, atropine and verapamil were effective in some cases.(ABSTRACT TRUNCATED AT 250 WORDS)
Department of Laboratory Medicine, Oita Medical University.