Unusual examples of supraventricular re-entrant tachycardias.

Programmed electrical stimulation of the heart uncovered unusual findings in four patients suffering from supraventricular tachycardias. They included 1) two supraventricular tachycardias of different location and frequency in the same patient, 2) increase in rate of a re-entrant atrioventricular (A-V) nodal tachycardia followed by the development of 2-to-1 A-V block, 3) a "gap" in A-V conduction and A-V nodal re-entrant tachycardia with 2-to-1 A-V block, and 4) the initiation of atrial re-entrant tachycardia by ventricular premature beats. The examples are given to help elucidate the understanding of mechanisms involved in re-entrant tachycardias and to localize the site of the re-entry circuit.