Accuracy of the Unipolar Electrogram for Identification of the Site of Origin of Ventricular Activation

Abstract

While an R wave in the unipolar electrogram can be seen as close as 2 mm from the site of impulse origin, the absence of an R wave as an indicator of the site of impulse origin in the right ventricle is highly inaccurate. Therefore, the absence of an R wave in the unipolar electrogram is unlikely to be an adequate guide for identification of an effective target site for ablation of right ventricular tachycardia.

Catheter Ablation of Ventricular Arrhythmias Arising from the Right Ventricular Septum Close to the His Bundle: Features of the Local Electrogram at the Optimal Ablation Site

“…The peak deflection of the bipolar electrogram usually coincides with the steepest intrinsic deflection of the 2 local unipolar recordings 15,16 . On the contrary, a slow initial negative slope of the unipolar recording suggests that the electrogram is a far‐field signal, generated by tissue some distance from the mapping catheter 14–16 . In the present study, most of the local electrograms at the successful ablation site of the VAs arising from the RV outflow tract revealed a QS morphology with a steep downstroke in the unipolar electrogram and a great maximum peak of the R wave with a steep upstroke in the bipolar electrogram.…”

Venice Chart International Consensus Document on Ventricular Tachycardia/Ventricular Fibrillation Ablation

“…Electrograms may be recorded with unipolar, bipolar, and/or combinations of both recording methods as each has different advantages and weaknesses. Unipolar recordings are typically obtained with minimal filtering (e.g., high‐pass filter corner frequency set to 0.5 Hz or lower), in which case the morphology of the recordings provides potentially useful information 86–88 . A QS configuration is typically seen at the origin of focal arrhythmias.…”

Optimal ablation strategies for different types of ventricular tachycardias

“…Firstly, the spatial resolution of bipolar activation mapping might be limited by initial rapid endocardial activation away from the site of origin. 47 Secondly, because a QS pattern in electrograms from unipolar electrodes might not be adequate by itself for identifying a suitable ablation site, 48 Key points ■ The optimal ablation strategy for ventricular tachycardia is determined by the site of origin and the electrophysiological mechanism ■ Prediction of the origin site requires consideration of surface electrocardiographic findings, ascertainment of the underlying cardiac disease (if any), and identification of regions of myocardial scarring using imaging modalities ■ Electrophysiological activation mapping to locate the earliest ventricular activation during focal ventricular tachycardias, and mid-diastolic potentials during re-entrant ventricular tachycardias, is the gold standard for identifying the substrate ■ When activation mapping of scar-related ventricular tachycardias is not possible, substrate mapping during sinus rhythm (to identify late or isolated diastolic potentials) is the preferred option ■ Catheter ablation of ventricular tachycardias is most often successful with an endocardial approach, but epicardial ablation using transvenous or subxiphoidal intrapericardial approaches is sometimes successful ■ Special ablation strategies might be required for unusual forms of ventricular tachycardias-those with intramural substrates or associated with electrical storm this technique should be used to supplement bipolar activation mapping. When ventricular tachycardias originate from specific sites, such as the aortic root or Purkinje network, a ventricular prepotential or Purkinje potential, respectively, are usually recorded at the proposed ablation sites.…”