ANATOMIC, ELECTRICAL, AND MECHANICAL FACTORS AFFECTING BIPOLAR ENDOCARDIAL ELECTROGRAMS - IMPACT ON CATHETER ABLATION OF MANIFEST LEFT FREE-WALL ACCESSORY PATHWAYS

Background The use of bipolar endocardial electrogram characteristics to guide radiofrequency (RF) current catheter ablation of accessory pa thways (APs) has been advocated by several investigators. However, the influences of a varying anatomy of the AP and the atrioventricular gr oove, of different ablative approaches, and of RF current pulses prece ding the final pulse have not been adequately addressed. Methods and R esults Local bipolar endocardial electrograms were retrospectively ana lyzed in a uniform cohort of 62 consecutive patients with a single man ifest AP located on the left free wall; in all patients, the AP had be en ablated by a uniform approach with a single catheter advanced retro gradely toward the mitral annulus. Electrogram parameters assessed wer e the presence or absence of a presumed AP potential, the atrial-to-ve ntricular (AIV) amplitude ratio, the A-V interval, and the onset of de lta wave to local ventricular activation (Delta-V) interval. The AP lo cation was classified on fluoroscopy as anterior, lateral, or posterio r. Catheter stability was verified by comparing pre- and post-RF ampli tudes of local atrial potentials. The ablation site was ventricular in 52 patients (group A) and atrial in 10 (group B). In group A, 26 APs (50%) required a single RF current pulse for ablation. These APs showe d no anatomic predilection and no statistically significant difference s in electrogram parameters from 24 APs that were ablated only after a median of three pulses had failed, suggestive of a wider ventricular insertion of the latter APs. A lower AIV ratio and a higher incidence of transient AP block found in the remaining 2 group A patients, who h ad anteriorly located APs requiring >10 failed pulses, suggested an ad verse anatomy of the A-V groove in that region. A stepwise multivariat e logistic regression analysis revealed that the simultaneous presence of (1) a presumed AP potential, (2) an A/V ratio greater than or equa l to 0.10, (3) an A-V interval less than or equal to 40 milliseconds, and (4) a Delta-V interval less than or equal to 0 milliseconds was as sociated with a specificity of 94% and a positive predictive accuracy of 87% for an RF pulse to be successfully applied to the ventricular i nsertion to the AP. Compared with APs of group A, APs of group B were distinguished by unsuccessful ventricular pulses associated with a Del ta-V interval >10 milliseconds in the presence of an A/V ratio >0.33 ( specificity of 97% and positive predictive accuracy of 82%), which is suggestive of a more epicardial ventricular insertion of these APs. Co nclusions The effect of anatomic variations of the AP and the A-V groo ve is reflected in the bipolar endocardial electrogram and needs to be considered in the approach to AP ablation. The stepwise inclusion of the four electrogram criteria introduced in this study may improve the efficacy of RF catheter ablation of a manifest left free-wall AP at i ts ventricular insertion. Whenever mapping cannot improve on a Delta-V interval >10 milliseconds despite apparently close contact with the m itral annulus (''good'' A/V ratio), attempts at ablation are likely to be successful at the atrial aspect of the mitral annulus.