Abstract 17250: It's the Journey, Not the Destination: Demonstration of an Uncommon Variation of Para-Hisian Pacing

Abstract

A 21 year-old college athlete presented with palpitations during exercise. ECG and transthoracic echo were normal. He underwent electrophysiology study. With catheter placement, the patient had atrial fibrillation without preexcitation. On isoproterenol, spontaneous salvos of supraventricular tachycardia (SVT) occurred. Coronary sinus activation was concentric. SVT never sustained, limiting diagnostic maneuvers. In SVT, the ventriculoatrial (VA) time was 145 msec, and there was no decrement of VA conduction with ventricular extrastimuli. Para-Hisian pacing (PHP) was performed. At high output, local myocardial + Purkinje (LM+P) capture was observed, with a VA time of 130 msec; at lower output, selective Purkinje (SP) capture was observed, with a narrower QRS (Figure 1A), and paradoxically longer VA time (160 msec) (Figure 1B). The diagnosis of a retrograde conducting-only accessory pathway (AP) was made, mapped with ventricular pacing, and ablated on the posteroseptum. SVT was no longer inducible. Discussion: PHP is employed to identify presence of a septal retrograde conducting AP based on findings of equal VA times with LM and LM+P capture. Here, the traditional findings of PHP (LM and LM+P capture) were absent because LM capture did not occur, and a third, distinct manner of activating the ventricle (via SP capture) produced unexpected results. In the presence of a retrograde conducting AP, the VA time with narrow-QRS by way of SP capture (sequential activation of the Purkinje system then myocardial conduction) was paradoxically longer than that of wider-QRS LM+P capture (concurrent Purkinje and myocardial conduction), because the path of VA conduction via the AP is “closer” to the site of first ventricular activation. The comparison of SP to LM+P capture may in and of itself declare the presence of an AP; however, LM, LM+P, and SP capture together may be useful to identify a second concealed AP providing incremental diagnostic information to conventional PHP.