Electrophysiological Features Differentiating the Atypical Atrioventricular Node–Dependent Long RP Supraventricular Tachycardias

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Background— Diagnosing atypical atrioventricular node-dependent long RP supraventricular tachycardias (SVTs) can be challenging. Methods and Results— Nineteen patients with 20 SVTs (atypical atrioventricular nodal reentrant tachycardia without [n=11]/with [n=3] a bystander nodofascicular [NF] accessory pathway, orthodromic reciprocating tachycardia [ORT] using a decremental atrioventricular [permanent form of junctional reciprocating tachycardia; n=4] or NF [NF reentrant tachycardia; n=2]) accessory pathway underwent electrophysiological study. Postpacing interval (PPI)–tachycardia cycle length (TCL), corrected PPI, ∆VA (ventriculoatrial), ∆HA (His-atrial), ∆AH (atrio-His) values, and responses to His-refractory ventricular premature depolarizations were studied. Compared with atrioventricular nodal reentrant tachycardia, ORT patients were younger (42±13 years versus 54±19 years; P =0.036) and were women (5/6 [83%] versus 3/14 [21%]; P =0.036); TCLs were similar (435 ms versus 429 ms; 95% confidence interval, −47.5 to 35.5). PPI–TCL was shorter for ORT (118 ms versus 176 ms; 95% confidence interval, 26.3–89.7) but only 50% had PPI–TCL <115 ms, whereas 5 of 6 (83%) had PPI–TCL <125 ms (sensitivity, 83%; specificity, 100%). Corrected PPI <110 ms, ∆VA <85 ms, and ∆HA <0 ms had equivalent sensitivity (67%) and 100% specificity for ORT. Compared with permanent form of junctional reciprocating tachycardia, NF reentrant tachycardia/atrioventricular nodal reentrant tachycardia had longer ∆AH (29 ms versus 10 ms; 95% confidence interval, 3.03–35.0) or AH (SVT) <AH (NSR) (normal sinus rhythm) His-refractory ventricular premature depolarizations advanced (4/8 [50%]), delayed (4/8 [50%]), or terminated (5/8 [63%]) SVT in all accessory pathway patients. Conclusions— This unusual SVT requires separate maneuvers to delineate its upper and lower circuit. Standard entrainment criteria are modestly sensitive but highly specific for ORT; and PPI–TCL of 125 ms seems better than 115 ms. The ∆AH criteria, or paradoxically AH (SVT) <AH (NSR) , differentiates NF reentrant tachycardia/atrioventricular nodal reentrant tachycardia from permanent form of junctional reciprocating tachycardia. Bystander accessory pathways were only identified by His-refractory ventricular premature depolarizations.