Significance of QRS Alternans During Narrow QRS Tachycardias

The three general types of paroxysmal supraventricular tachycardia (PSVT) are atrioventricular (AV) nodal reentrant tachycardia, orthodromic AV reciprocating tachycardia utilizing an accessory AV connection for retrograde conduction from the ventricle to the atrium, and atrial tachycardia. The electrocardiographic criteria used to distinguish these types of PSVT have focused on the P wave and have been based on analysis of its location relative to the QRS complex or its electrical axis. In 1983, Green, et al. proposed that an additional criterion useful for determining the mechanism of narrow QRS PSVT may be QRS alternans, with the presence of QRS alternans being indicative of orthodromic AV reciprocating tachycardia [Fig. 1).̂ However, subsequent studies by other investigators have yielded conflicting results, and the diagnostic value of QRS alternans remains controversial. In this review, the available data on the diagnostic value of QRS alternans during narrow QRS PSVT will be summarized and the possible mechanisms of QRS alternans will be discussed.

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