End Points for Ablation of Scar-Related Ventricular Tachycardia

Abstract

T he goal of catheter ablation strategies for the treatment of scar-related ventricular tachycardia (VT) is the interruption of critical areas of slow conduction within the VT circuits responsible for the development and maintenance of VTs. 1,2 Clinical studies have consistently shown the superiority of radiofrequency catheter ablation compared with standard medical therapy in controlling recurrent VT. 3,4 However, even after an acutely successful ablation, the long-term freedom from recurrent VT remains suboptimal, especially in patients with nonischemic substrates where the recurrence rates for longterm follow-up can be as high as 77%.5 Identification of the optimal end points for VT ablation is crucial to improve the success rate of this procedure. The response to programmed electric stimulation (PES) at the end of the procedure has been traditionally used to evaluate the acute success and predict longterm outcomes.1,2 Noninducibility by PES represents a classical end point for VT ablation and the only 1 endorsed by the current practice guidelines.1,2 Of note, a direct association between VT noninducibility at the end of the procedure and long-term arrhythmia-free survival has been suggested but not uniformly demonstrated. 4,[6][7][8][9] More recently, the increasing adoption of substrate-based ablation techniques, which target specific electrograms indexing slow conduction (ie, abnormal, split, and late electrograms) in sinus rhythm and reasonable surrogates for the VT isthmus, 10,11 has been paralleled by an increasing need for new ablation end points. Although noninducibility at PES has been used as an end point also in studies evaluating substratebased ablation approaches, other procedural end points have been described to validate the completeness of linear lesions and the elimination of abnormal potentials within the scar. This review will summarize the state of the art regarding procedural end points for catheter ablation of scar-related VT (Table 1). Invasive PESNoninducibility at PES represents the most widely accepted end point for catheter ablation of scar-related VT. The most recent expert consensus document on VT ablation endorses noninducibility of the presumed clinical VT as the minimum end point for catheter ablation of scar-related VT; other end points beyond noninducibility are discussed but not specifically endorsed, because they have not been systematically validated.1,2 The bulk of the evidence supporting noninducibility at PES as a procedural end point derives from studies including patients with infarct-related VT (Table 2). Early experiences with catheter ablation in this clinical setting reported a significant association between noninducibility at the end of the procedure and VT-free survival.12-16 Subsequent studies including larger patient populations have provided mixed results. 4,6,7,9,12,13,15,[17][18][19][20][21][22][23][24][25][26][27] It is important to emphasize that none of these studies was specifically designed to perform a formal longitudinal evaluation of noninducibili...

Substrate mapping for unstable ventricular tachycardia

“…We have recently proposed different endpoints to assess the efficacy of point lesions and to establish block across a line. 5 These include: loss of high-frequency signals representing near-field activation, electrical unexcitability with high output pacing, change in pace-map morphology with pacing from opposite sides of the ablation line and activation mapping techniques to confirm block across a line. 5 All these suggested endpoints warrant validation in adequately designed clinical studies.…”

“…Finally the need for post-ablation remapping to validate the total elimination of late potentials from different pacing sites needs to be determined. 5 …”

“…1,3,4 The main procedural endpoint is the interruption of crucial areas of slow conduction responsible for the development and maintenance of the reentrant VT circuit. 5 This can be best achieved through an accurate characterization of the VT circuitry by means of activation and entrainment mapping, which requires the VT to be stable and hemodynamically tolerated. However, the majority of patients presenting for catheter ablation have unstable tachycardias that prevent an accurate definition of the critical areas of the reentrant circuit with activation or entrainment mapping.…”

Impact of Electrode Type on Mapping of Scar‐Related VT

“…[5][6][7][8][9] High-density mapping is of critical value for accurate scar visualization as well as for identification of ablation targets such as LAVA. 10,11 Creation of maps for substrate-based ablation is currently predominantly performed using ablation catheters with bipolar recording from the distal ablation electrode of a typical size of 3.5 -4 mm tip length, placed at an end-to-end distance of 1 -2.5 mm from the proximal ablation electrode that has a size of 1.3 -2 mm tip length. In addition, contact plays a role in the measured voltage as insufficient catheter contact can artificially produce a low-voltage area.…”

Ablation of ischemic ventricular tachycardia

“…Absence of inducible ventricular tachycardia has been associated with better outcome [49], but has the limitation of the probabilistic nature of ventricular tachyc ardia inducibility. The predictive accuracy of programmed stimulation has also been disappointing [50]. Ventricular tachycardia recurrence has been observed in 29% of patients who were rendered noninducible acutely [51]; this may reflect healing and contraction of initial radiofrequency lesions [52].…”