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

Figures

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  Figure 1. Theoretical basis of induction indices during ventricular pacing. A: During induction, the interval from the last ventricular pacing stimulus to the first ventricular electrogram of tachycardia (induction postpacing interval) represents conduction from the pacing site to the tachycardia circuit, 1 rotation within the circuit, and return conduction to the ventricle. A functional block in 1 limb of the dual pathways and unidirectional conduction allows the initiation of reentry. B: During ventricular overdrive pacing, the orthodromic (N) and antidromic (N–1) wavefronts continuously reset the circuit, creating a stable state. After pacing cessation, the postpacing interval is measured, reflecting conduction through the same components during entrainment. Thus, induction postpacing interval–tachycardia cycle length conceptually parallels postpacing interval–tachycardia cycle length as an estimate of extracircuit conduction time. AT = atrial tachycardia; AVN = atrioventricular node; AVNRT = atrioventricular nodal reentrant tachycardia; FP = fast pathway; ORT = orthodromic reciprocating tachycardia; SP = slow pathway; VOP = ventricular overdrive pacing; VP = ventricular pacing.

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  Figure 2. Intracardiac EGMs during induction of supraventricular tachycardias. A: AT induced by ventricular burst pacing with a ventricular–atrial–atrial–ventricular sequence; the EAAS shifted from the CS ostium during ventricular pacing to the HRA during the AT (iPPI 934 ms). B: Fast–slow AVNRT induced by ventricular extrastimuli with a ventricular–atrial–ventricular sequence; the EAAS remained at the CS ostium (iPPI 534 ms). C: ORT using a right free-wall accessory pathway induced by ventricular extrastimuli with a ventricular–atrial–ventricular sequence; the EAAS remained at the CS ostium (iPPI 402 ms). AT = atrial tachycardia; AVNRT = atrioventricular nodal reentrant tachycardia; CS = coronary sinus; EAAS = earliest atrial activation site; EGM = electrogram; HRA = high right atrium; iPPI = induction postpacing interval; ORT = orthodromic reciprocating tachycardia.

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  Figure 3. Influence of AH prolongation on the iPPI measurement. Intracardiac EGMs during the induction of posterior-septal ORT showing marked prolongation of iPPI–TCL owing to atrioventricular nodal decremental conduction. A: Septal ORT induced by ventricular extrastimuli with a ventricular–atrial–ventricular sequence; the EAAS was recorded on the CS 5–6. The iPPI and iPPI–TCL were 622 and 222 ms, respectively. The AH interval at initiation was longer than that during tachycardia (380 vs 216 ms). B: VOP during the ORT. After pacing cessation, tachycardia resumed with a ventricular–atrial–ventricular sequence; PPI was 586 ms. Although the PPI–TCL was 186 ms, AH correction reduced the corrected PPI–TCL to 52 ms. Applying the same correction, the corrected iPPI–TCL was 86 ms. AV = atrioventricular; EAAS = earliest atrial activation site; EGM = electrogram; iPPI = induction postpacing interval; PPI = postpacing interval; TCL = tachycardia cycle length; VOP = ventricular overdrive pacing.

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  Figure 4. Comparison of induction ventricular intervals across SVTs. Dot plots of iPPI–TCL (A) and corrected iPPI–TCL (B) in AT, AVNRT, and ORT. AH correction was applied only to AVNRT and ORT with a ventricular–atrial–ventricular response. Differences were significant overall (P < .001) and for all pairwise comparisons (P < .05). AT = atrial tachycardia; AVNRT = atrioventricular nodal reentrant tachycardia; iPPI = induction postpacing interval; ORT = orthodromic reciprocating tachycardia; TCL = tachycardia cycle length.

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  Figure 5. Correlation between iPPI–TCL and PPI–TCL. Scatter plots in 67 entrained AVNRT/ORT cases with regression lines and 95% CIs: iPPI–TCL vs PPI–TCL (r = 0.685; P < .001) (A) and corrected iPPI–TCL vs corrected PPI–TCL (r = 0.948; P < .001) (B). AVNRT = atrioventricular nodal reentrant tachycardia; CI = confidence interval; iPPI = induction postpacing interval; ORT = orthodromic reciprocating tachycardia; PPI = postpacing interval; TCL = tachycardia cycle length.

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  Figure 6. Diagnostic performance of iPPI–TCL for ORT. Receiver operating characteristic curves for iPPI–TCL (A) and corrected iPPI–TCL (B) to differentiate ORT from AVNRT. AUCs are shown; optimal cutoffs were determined by the Youden index. AUC = area under the curve; AVNRT = atrioventricular nodal reentrant tachycardia; iPPI = induction postpacing interval; ORT = orthodromic reciprocating tachycardia; TCL = tachycardia cycle length.

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  Figure 7. Diagnostic separation between AVNRT and septal ORT. Dot plots of iPPI–TCL (A) and corrected iPPI–TCL excluding AT (B) (n = 10). When ORTs were subclassified into free-wall (n = 35) and septal ORT (n = 6), iPPI–TCL largely separated AVNRT from septal ORT, with 1 overlapping case, whereas corrected iPPI–TCL exhibited complete separation. Using the conventional PPI–TCL thresholds as references, iPPI–TCL of ≤115 ms and corrected iPPI–TCL of ≤110 ms identified septal ORT with sensitivities/specificities of 83.3%/100% and 100%/100%, respectively. Exploratory cutoffs (iPPI–TCL ≤125 ms; corrected iPPI–TCL ≤106 ms) performed similarly in this cohort. AT = atrial tachycardia; AVNRT = atrioventricular nodal reentrant tachycardia; iPPI = induction postpacing interval; ORT = orthodromic reciprocating tachycardia; PPI = postpacing interval; TCL = tachycardia cycle length.