Tachycardia cycle length alternans in orthodromic reciprocating tachycardia due to mutually dependent dual AV node physiology and retrograde supernormal conduction

Excerpt

A 31-year-old woman was found to have orthodromic atrioventricular reciprocating tachycardia (ORT) utilizing a left lateral accessory pathway (AP) with tachycardia cycle length (TCL) alternans. Dual AV nodal physiology accounted for the anterograde cycle length variation but the etiology of retrograde cycle length variation, or the ventriculo-atrial interval (VAI), measured between the onset of the surface QRS complex and the earliest atrial activation on the CS catheter, may represent supernormal conduction wherein rapid VAI times (64 ms) are observed following anterograde fast pathway conduction (163 ms), and longer VAI times (102 ms) are observed following anterograde slow pathway conduction (252 ms). Extrastimulation pacing identified no other AP, and this was confirmed with detailed activation mapping, which also demonstrated that the earliest site of atrial activation was indeed left lateral. A single ablation eliminated AP conduction in less than 10 s and rendered ORT non-inducible. Nagashima et al. noted that intraventricular conduction velocity was enhanced in certain ORT patients [1]. They postulated that enhanced propagation or supernormal conduction between the proximal Purkinje-muscle junction was triggered by faster heart rates, consistent with our case wherein rapid VAI times were observed following anterograde fast pathway conduction, (Fig. 1) [1].

…