Induction Indices during Ventricular Pacing as an Alternative Diagnostic Tool in Supraventricular Tachycardias

<h2>Abstract</h2><h3>Background</h3> Pacing maneuvers are fundamental for differentiating supraventricular tachycardia (SVT) mechanisms, but interpretation may be limited when tachycardia cannot be sustained. <h3>Objective</h3> To determine whether SVT induction indices during ventricular pacing (VP) provide diagnostic information comparable to conventional ventricular overdrive pacing (VOP). <h3>Methods</h3> We retrospectively analyzed 92 SVTs (91 patients) induced by VP: 10 atrial tachycardias (AT), 41 atrioventricular nodal reentrant tachycardias (AVNRT), and 41 orthodromic reciprocating tachycardias (ORT). The induction ventriculo-atrial (iVA) sequence and induction post-pacing interval (iPPI), defined as the interval from the last VP stimulus to the first ventricular electrogram of induced SVT, were assessed. The difference between the iPPI and tachycardia cycle length (iPPI–TCL) was compared with the conventional post-pacing interval (PPI)–TCL in cases successfully entrained by VOP. <h3>Results</h3> All ATs were induced with a V-A-A-V sequence, whereas all AVNRT and ORT exhibited a V-A-V sequence, fully concordant with post-VOP sequences. The iPPI–TCL was significantly longer in AVNRT than ORT (180 [150, 201] vs. 80 [50, 129] ms; p<0.001) and correlated with the PPI–TCL (r=0.685, p<0.001). After atrial–His correction, the corrected iPPI–TCL strongly correlated with the corrected PPI–TCL (r=0.948, p<0.001). A corrected iPPI–TCL cutoff of ≤110 ms differentiated ORT from AVNRT with 90.2% sensitivity and 100% specificity and identified septal ORT without misclassification. <h3>Conclusions</h3> The iVA sequence reliably differentiated AT from AVNRT/ORT, and the iPPI–TCL closely paralleled conventional PPI–TCL. Induction indices during VP may serve as practical alternatives when PPI measurements are not feasible.