Contact Force During VT Ablation: Vector Orientation Is Key

A. Aryana, A. d'Avila
2014 Circulation: Arrhythmia and Electrophysiology  
O ur understanding of ventricular tachycardia (VT) substrate and mapping has evolved considerably over the past 3 decades. Nonetheless, the outcomes of catheter ablation of scar-mediated VT continue to remain far from perfect. 1 There is no doubt that new advances in VT mapping may help improve the outcomes of catheter ablation. But ultimately it will be the quality of the ablation lesions delivered to the VT substrate that will determine the clinical outcomes. This is important because
more » ... quency, the principal source of energy used in VT ablation has been presumed to be a suboptimal energy modality for catheter ablation of scar tissue. A recent study found that in experienced hands using the standard 3.5-mm tip irrigated ablation catheter, elimination of late potentials occurred during only one-third of the radiofrequency applications and electrogram reduction with impedance drop >10 Ω in just half of the radiofrequency lesions during VT ablation. 2 Yet, experimental data suggest that presence of scar by itself does not significantly impact lesion size or intramural temperatures when stable ablation catheter-tissue contact is maintained during radiofrequency energy delivery through a needle electrode. 3 As such, there seems to be a paradox-scar by itself does not significantly affect radiofrequency lesion size or intramural temperature during ablation, however, the efficacy of ablating scar tissue seems poorer than anticipated! Because tissue contact by way of a needle electrode seems most optimal, one may simply ask whether lack of a stable catheter-tissue contact could provide a plausible explanation for our disappointing clinical outcomes. Article see p 1168 Although no concrete data are presently available to support a direct relationship between contact force (CF) and successful elimination of abnormal ventricular electrograms or VT recurrence after catheter ablation, it is conceivable that poor or unstable contact between the ablation catheter tip and myocardial tissue could gravely impact VT ablation outcomes. Sacher et al 4 have previously shown that lesion formation during radiofrequency ablation could significantly improve in nearly one quarter of the applications with the aid of CF feedback. CF also seems to be the principal determinant of epicardial radiofrequency lesion size, steam pops, acute coronary artery, and phrenic nerve injury. 5 In fact, ablation using sufficiently high CF has even been shown to create small myocardial radiofrequency lesions at sites covered by thick epicardial fat (>3.5 mm) 5 -that is, epicardial sites at which the heavy fat layer would otherwise seriously impede radiofrequency lesion formation. Although the optimal CF for ventricular mapping and ablation has yet to be determined, in this issue of Circulation: Arrhythmia and Electrophysiology, Jesel et al 6 provide important insights into regional variations in CF and catheter orientation relating to epicardial and endocardial mapping. Briefly, the authors evaluated CF variability using a cooled-tip mapping/ablation catheter (Thermocool SmartTouch, Biosense Webster, Inc, Diamond Bar, CA) during endocardial and epicardial mapping in a cohort of patients with and without structural heart disease undergoing catheter ablation of VT, by 2 experienced operators blinded to the collected CF data. Several findings from this article are noteworthy. First, bipolar signal amplitude in healthy endocardial and epicardial tissue was found to increase with CF ≤10 g, but not beyond. As such, based on a general linear mixed model analysis, the best CF cutoff value for obtaining a signal amplitude >1.5 mV was determined to be 7 g in the left ventricular (LV) endocardium (sensitivity: 80%, specificity: 75%), 9 g in the right ventricular (RV) endocardium (sensitivity: 65%, specificity: 83%), and 4 g in the epicardium (sensitivity: 83%, specificity: 64%). These findings are also consistent with other published reports. Similarly, Mizuno et al 7 recently showed that the optimal CF cutoff value to predict adequate tissue contact during LV endocardial and epicardial mappings was 9 g. Second, the authors detected no significant differences between transseptal and retrograde LV mapping strategies, with the exception of a higher incidence of greater CF (defined by >20 g) observed with the transseptal approach. CF was shown to be lower on the LV basal septal and anterobasal regions with either transseptal or retrograde mapping and also low on the RV septal and apical regions, whereas CF was greatly improved with transseptal mapping of the LV apical septal and apical inferior regions and mapping of the RV free wall. This is notable and calls for greater attention during mapping and ablation of the RV, as free wall perforations can occur with vigorous catheter manipulations in this area often posing catastrophic consequences. Meanwhile, epicardial CF was greatly reduced in the apical and lateral LV segments even in presence of optimal catheter orientation. Nonetheless, it should be emphasized that some of these findings may have (Circ Arrhythm Electrophysiol.
doi:10.1161/circep.114.002389 pmid:25516578 fatcat:pjcfrkteancjfiq75qbo62ocyy