[Electric alternans of QRS: its electrophysiologic significance in narrow QRS supraventricular paroxysmal tachycardia].

The results of 22 patient's transesophageal electrophysiologic studies were analyzed to value the meaning of QRS alternans during narrow QRS tachycardia. Standard ECG showed ventricular pre-excitation in eight patients. QRS alternans were in six of them: heart rate was included between 230 and 374 m/sec (301.8 +/- 42 m/sec); in the remaining 16 patients, heart rate was included between 240 and 450 m/sec (350.0 +/- 42 m/sec). Our findings suggest that QRS alternans is related to the rate of tachycardia rather than to the presence of an accessory pathway.