In patients with atrioventricular (A V) nodal re entrant paroxysmal supraventricular tachycardia (PSVT), atrial extrastimulus technique frequently reveals discontinuous A1-A2, H1-H2 curves suggestive of dual A V nodal pathways. To further test the hypothesis that these curves in fact reflect dual A V nodal pathways, a ventricular extrastimulus (V8) was coupled either to A2 at a fixed A1-A2 interval which reliably produced an A V nodal re entrant atrial echo (E) with a constant A2-E interval in two patients, or to QRS complex (V) during sustained PSVT with a constant E E interval in one patient. Three response zones were defined: at longer A2-V8 or V-V8 coupling intervals, V8 manifested no effect on the timing of E (Zone 1). At closer A2-V8 or V-V8 coupling interval, V8 conducted to the atrium, shortening the apparent A2-E or E E interval (Zone 2). At shortest A2-V8 or V-V8 coupling interval V8 was blocked retrogradely, and no E was induced (Zone 3). The ability of V8 to preempt control of the atria (Zone 2 response) strongly suggests the presence of dual A V nodal pathways in these PSVT patients. If only a single pathway were present, V8 would of necessity collide with the antegrade impulse and could not reach the atria. The Zone 3 response occurs because of retrograde refractoriness of the fast pathway. Failure of the echo during Zone 3 probably reflects concealed conduction to the fast pathway, or possibly interference in the slow pathway.
ASJC Scopus subject areas
- Cardiology and Cardiovascular Medicine
- Physiology (medical)