Substrate mapping for unstable ventricular tachycardia.

The primary goal of catheter ablation of scar-related ventricular tachycardia (VT) is the interruption of critical areas of slow conduction responsible for the development and maintenance of the reentrant VT circuit. Most patients with scar-related VT present with unstable arrhythmias that are not amenable to interrogation from multiple sites to define the VT circuit based on the intracardiac activation sequence and the response to entrainment mapping. In order to effectively target unstable VTs, a number of ablation approaches have been described with the aim of targeting the abnormal substrate defined with mapping in sinus or paced rhythm. Some of these strategies (eg, late potential and local abnormal ventricular activity ablation or scar homogenization) target the entire abnormal substrate harboring abnormal electrograms, defined with a variety of different criteria. Scar dechanneling, linear ablation through sites matching VT with pacing, and the core isolation approach focus on more discrete regions within the abnormal substrate that have been proven relevant to the clinical and/or inducible arrhythmias by means of physiologic maneuvers, although this does not necessarily translate to fewer radiofrequency lesions to achieve the procedural end-point. Observational studies evaluating different substrate-based ablation techniques have reported fairly uniform arrhythmia-free survivals at short- and mid-term follow-up, although direct comparisons between different techniques are lacking. In this article, we summarize the different state-of-the-art substrate mapping and ablation approaches for targeting unstable VT, with a particular focus on the relative merits and limitations of the described techniques.