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In this paper we report the first adult case of an "idiopathic" ventricular bidirectional tachycardia (BT), in a 57 year old woman. The tachycardia, at the time of our observation, was incessant in type and had a slightly irregular frequency of about 140 bpm. BT initiated and terminated abruptly, without any temporal relationship to the preceding RR interval, or the QRS morphology. The interval between the two alternating QRS patterns often varied over a wide range of values. The BT could be interrupted only by overdrive atrial and ventricular stimulation, but promptly reappeared as pacing was discontinued. Therapy with quinidine associated with propranolol was effective on a long term trial. The vectorcardiographic analysis and the electrophysiologic investigation demonstrated a ventricular origin of the BT, localizing its site of origin to common myocardial tissue, probably near the two left hemifascicles. Our data could not elucidate the electrogenetic mechanism of this ventricular arrhythmia, because of its chaotic behavior.

Bidirectional tachycardia. A sustained form, not related to digitalis intoxication, in an adult without apparent cardiac disease.