[Electrophysiologic significance of the electric alternans in supraventricular tachycardia].

To investigate the electrophysiologic significance of QRS alternans during narrow QRS tachycardia, transesophageal atrial pacing and recording was performed in 24 patients with a history of paroxysmal supraventricular tachycardia. Standard electrocardiograms (ECG) showed ventricular preexcitation in 15 patients and normal QRS pattern in 9. The ventriculo-atrial interval during tachycardia, as defined by means of transesophageal electrogram, allowed tentative diagnosis of the tachycardia mechanism. A 12-lead ECG was recorded either during spontaneous or induced tachycardia, as well as during transesophageal atrial pacing at increasing rates. Electrical alternans occurred spontaneously in 8 patients (33%, Group A): 5 with accessory pathway reentry (mean VA: 136 +/- 43 ms), 3 with intranodal reentry (mean VA: 48.3 +/- 43 ms). Tachycardia rate ranged between 170 and 230 b/min (mean 200.7 +/- 16). In 2 patients alternation of the QRS occurred only in the presence of a heart rate exceeding 180 and 190 b/min, respectively. The amplitude of QRS remained stable during tachycardia in 16 patients (67%, Group B): 14 with accessory pathway reentry (mean VA: 137.5 +/- 32 ms), 2 with intranodal reentry (mean VA: 45 +/- 7 ms). In this group, the tachycardia rate ranged from 150 to 210 b/min (mean 175 +/- 12). Incremental transesophageal atrial pacing up to rates equal to that of tachycardia was performed in 5 patients of Group A and in 8 of Group B. Electrical alternans could not be induced in both groups with pacing at progressively increasing rates. In contrast, the phenomenon was elicited in 2 patients of Group A when an abrupt pacing at the same rate that had showed the spontaneous occurrence of QRS alternans was instituted.(ABSTRACT TRUNCATED AT 250 WORDS)