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European Heart Journal 1995 16(5):667-673;
Copyright © 1995 by the European Society of Cardiology.
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© 1995 The European Society of Cardiology

Physiological and pathological responses of TU waves to class Ia antiarrhythmic drugs

T. MARUYAMA, T. OHE, T. KURITA, N. AIHARA and W. SHIMIZU

The Division of Cardiology, National Cardiovascular Center 5-7-1. Fujishirodai, Suita, Osaka, 565, Japan

revised 7 October 1994; accepted 28 October 1994.

Correspondence: Takahisa Maruyama. The 2nd Department of Internal Medicine, Shinshu University School of Medicine, 3-1-1 Asahi. Matsumoto, Nagano. 390. Japan.

Abstract

Abnormal repolarization associated with torsades de pointes is expressed as QT prolongation. The physiological response to class la antiarrhythmic drugs is also reflected in prolongation of the QT interval. However, the essential difference between pathological and physiological prolongation is not clear.

The purpose of this investigation was to differentiate between pathological and physiological changes in the repolarization waves of surface electrocardiograms (ECG) induced by class la drugs. In 18 patients without a history of torsades de pointes or syncope (control group), TU waves were compared before and after the administration of class la drugs (physiological response). In eight patients with torsades de pointes induced by class la drugs (torsades de pointes group), the TU waves at torsades de pointes were compared with those before drug administration (pathological response). In the control group, although the QTc (measured in lead II and corrected for heart rate by Bazett's formula) was increased significantly (0.40±0.04 to 0.44 ±0.05 s, P<0.001), the U-amp (amplitude of the U wave measured in a precordial lead where the Tand U waves were clearly differentiated) remained unchanged. In the torsades de pointes group, however, the QTc was increased (0.42 ±0.04 to 0.54 ±0.07 s, P<0.02); the U-amp was also increased, significantly (0.09 ±0.07 to 0.27 ±0.18 mV, P<0.05). Thus, enlargement of the U wave may help to differentiate between the physiological and pathological responses to class la drugs.

Key Words: U wave • torsades de pointes • class la antiarrhythmic drugs


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