br Procedural endpoints The most commonly

Procedural endpoints The most commonly employed electrophysiological endpoint is the achievement of noninducibility. While noninducibility has been shown to be predictive for clinical freedom from recurrent VT, it has not been uniformly the case [1,2]. Inducibility of VT is probabilistic and rarely is reproducibly triggered on command. Further, anesthesia and antiarrhythmics may adversely impact the ease of VT induction. In one of the largest cohorts published to fate, Della Bella demonstrated that acute procedural endpoints were predictive of cardiovascular mortality [87]. As homogenization is increasingly being performed, an objective measure to demonstrate complete elimination of abnormal electrograms has not been established. Use of a multipolar mapping catheter may be useful to rapidly remap ablated regions to ensure abolition of late potentials [88]. In many cases, biophysical limitations may impair the ability to completely eliminate an electrogram. In other arrhythmias treated with linear lesions, bidirectional block has been shown to be the most robust electrophysiological endpoint. Potential objective endpoints would require remapping to demonstrate a change in scar propagation that would reflect a line of block or elimination of the latest regions of activation.
Ablation technology and intramural substrates With increased implementation of epicardial ablation, radiofrequency AI-3 delivered into scar from both surfaces of the myocardial wall has improved our ability to penetrate and modify scar. Irrigated ablation technology has been shown to optimize power delivery into tissue as heating of the catheter-tissue interface is mitigated. Cryoablation has been shown to create similar lesions dimensions on the epicardium and it often used in open surgical cases [89,90]. However, irrigated lesions delivered through fibrosis may still be limited. Myocardial regions that specifically remain a challenge are septal substrates and the LV summit. Bipolar radiofrequency ablation has been proposed to improve the depth of ablation lesions [91]. A retractable intramural needle, that can be inserted up to 8mm deep into the myocardium holds promise for tackling difficult substrated [92]. Alcohol and coil embolization of a feeding arterial branch to the targeted region have demonstrated efficacy [93,94]. Alternative energy sources like HIFU require technical optimization but may have a future role in VT ablation.
Randomized trials and guidelines Over the past two decades, there have been a paucity of randomized trials in VT ablation. This is attributable in part to referral bias and the inherent urgent nature of recurrent VT, which frequently presents as electrical storm. SMASH-VT was an investigator initiated randomized trial of 128 patients greater than 1 month postinfarction with a secondary prevention indication for ICD comparing preemptive ablation versus standard medical therapy [75]. After the study commenced, patients with primary prevention with an appropriate therapy were included to facilitate enrollment. Using a substrate based approach and entrainment when possible, patients that underwent preemptive catheter ablation had a significant reduction in ICD therapy at 2 years compared to those receiving medical therapy (12% vs. 33%, HR 0.35, p=0.007). The VTACH study was a prospective, randomized multi-center European trial examining the role of preemptive VT ablation prior to implantation of ICD for hemodynamically stable VT with prior infarction and EF <50% [95]. In 107 patients randomized, survival free of VT was 47% in the ablation group and 29% in the control group at 2 years (HR 0.61, p=0.045). Although these studies were not powered to assess for mortality, they advanced the notion of catheter ablation as an upfront strategy as opposed to a palliative procedure of last resort. Accordingly, the updated guidelines for VT ablation recommend ablation to be timed well before multiple ICD therapies ensue [96]. It should be noted that epicardial ablation was not performed in these two studies and the results can only be generalized to postinfarct substrates.