His bundle capture proximal to the site of bundle branch block: A novel pitfall of the para-Hisian pacing maneuver

Paced QRS morphology should be assessed to differentiate between complete loss of His bundle capture and loss of distal His bundle capture alone. This might be enough in patients with proximal right bundle branch block; however, in patients with proximal left bundle branch block, QRS morphology might be similar with loss of His bundle capture and with proximal His bundle capture. Introduction The para-Hisian pacing maneuver is useful in determining whether retrograde conduction is dependent on atrioventricular (AV) nodal conduction. Loss of direct His bundle capture results in a longer route for the depolarization wave to reach the AV node and the atrium, as it has to travel through the working myocardium to engage the distal Purkinje fibers. Thus, loss of direct His bundle capture results in obligatory ventriculoatrial (VA) interval prolongation unless a nonphysiological retrograde conduction route (an accessory pathway [AP]) is present. Consequently, a stable VA interval with loss of His bundle capture is considered diagnostic of the presence of an AP. This concept has been regarded as useful, especially when concentric retrograde atrial activation is present. Subsequently, however, potential important pitfalls in the interpretation of this differentiating maneuver were described. These include the recognition of inadvertent atrial capture, pure His bundle capture, the presence of fasciculoventricular pathways, and the impact of retrograde dual AV nodal physiology. A further reduction in pacing output or pushing the pacing catheter slightly deeper into the right ventricle to ensure pure right ventricular myocardial capture may be useful to avoid misinterpretation of proximal His bundle capture as pure right ventricular myocardial capture.