Prolongation of the tachycardia zone: a possible mechanism for medical failure in paroxysmal supraventricular tachycardia.

Paroxysmal supraventricular tachycardia in man has been considered to be due to either development of reentry utilizing AV junctional tissue or the presence of an ectopic pacemaker located within the atrium. Most contemporary information suggests that AV junctional reentry is the dominant mechanism for this arrhythmia in man. This present study identifies that the frequence of tachycardia episodes may be correlated with the width of a tachycardia zone as determined by the atrial extrastimulus technique. Moreover, pharmacological therapy directed toward the elimination of this arrhythmia can be assessed utilizing this atrial stimulation technique. Findings in this present study identify that, in patients with widened tachycardia zones, propranolol therapy may not be efficacious. This latter finding is no contrast to the previous observations suggesting that propranolol therapy is the drug of choice for reentrant arrhythmias in man.