A study on entrainment in various forms of tachycardias

In order to study the entrainment phenomenon in various forms of clinical and experimental tachycardia, overdrive pacing was performed in clinical paroxysmal supraventricular tachycardia (PSVT) of Wolff-Parkinson-White syndrome (6 cases), atrial flutter (AF-6 cases), ventricular tachycardia (VT-2 cases), experimental AF induced by Rosenblueth's method (5 dogs), and in VT induced by aconitine (5 dogs). Progressive fusion was demonstrated in all but aconitine-induced VT. After cessation of pacing, the first tachycardia complex showed no fusion at all, but the timing of the complex varied depending on the recording sites of the electrogram. The tachycardia complex occurred at the pacing rate only when the electrogram was recorded at the upstream of the pacing site along the reentry circuit in PSVT and experimental AF. In clinical VT, the complex appeared progressively later as the pacing rate was increased. In aconitine-induced experimental VT, the complex occurred at its original tachycardia rate originating from the site where aconitine was applied. In reentrant tachycardia, entrainment could be observed even when all three of the diagnostic criteria proposed by Brugada et al. were not fulfilled. The mechanism of tachycardia can be assessed by entrainment, although the proposed criteria should be reevaluated.