VOYAGE- Ventricular Tachycardia Ablation and Myocardial Scar Characterization With Magnetic Resonance

State of the art and preliminary data

Patients with structural heart disease (SHD) are at increased risk of VAs that can promote life-threatening events, for whom a proper treatment has a pivotal role. The use of antiarrhythmic drugs is limited due to their ineffectiveness in reducing related mortality or their common side effects. Implantable cardioverter defibrillator (ICD) can improve survival in a certain group of patients with SHD, but recurrent ventricular tachycardia (VT) needing ICD shocks reduce quality of life and probably patients survival. Moreover, ICD implant is affected by a noticeable risk of acute and chronic complications, that can reduce the survival of ICD recipient. Catheter ablation is an effective technique especially for the management of post-myocardial infarction ventricular tachycardia (post-myocardial infarction VT) and the recent VANISH trial showed that ablation reduced the composite primary outcome of death, VT storm or appropriate ICD shocks compared to patients with an escalation of amiodarone.

The introduction of a catheter in the ventricular chambers through a vascular access, allows to map the VT circuit that is usually inside the scar, and perform an ablation of the tissue responsible of the VAs substrate. The signals recorded by the catheter and the fluoroscopy images have been used to localize the target since 90s, but in the last decade the emergence of technological innovations, such as three-dimensional electroanatomic mapping (3D-EAM), has enhanced our ability to identify ablation targets. Three-dimensional electroanatomic mapping enables to generate a 3D reconstruction of any part of the heart without needing fluoroscopic navigation. Integration between anatomic and electrocardiographic (ECG) data it is very useful in choosing an optimal location for VA ablation, and the use of mapping systems contributed to reduce procedural, fluoroscopy and radiofrequency time. However, the efficacy of 3D-EAM can be suboptimal when we decide to follow a strategy of substrate ablation. Substrate ablation is characterized by an ablation of abnormal electrograms (EGMs) identified during sinus rhythm or ventricular pacing. In a recent meta-analysis, the combined risk of ventricular arrhythmia recurrence and all-cause mortality during long-term follow-up was lower when using a substrate-based approach compared to standard ablation of stable VT. However, efficacy was greatly reduced if the homogenization of the arrhythmic substrate was incomplete.

Real-time integration of anatomical VT substrate from data coming from cardiac image such as cardiac magnetic resonance (CMR) and multidetector computed tomography (CT) with EAM seems to improve efficacy of VA radiofrequency ablations and use of scar integration from imaging was an independent predictors of VT-free survival after catheter ablation in post-MI VT in recent papers. However, integration of CMR and CT images in the EAM system hasn't allowed to avoid, until now, an EAM that is time consuming, often imprecise and allowing only an incomplete substrate modification. Based on this consideration, we thought that an image integration taking into account not only the location of scar, but also its quantification and characterization could increase the efficiency of the ablation procedure, with an improvement of acute and chronic outcome. For this purpose, CMR has a pivotal role, allowing at characterizing the scar tissue via color-coded pixel signal intensity (PSI) maps that have a high correlation with the electroanatomic maps obtained during the ablation procedures. Particularly, the VT isthmuses found with the EAM correlated with the presence of heterogeneous tissue channels (HTCs) depicted in the PSI maps. Previous experiences demonstrated that these PSI maps can be imported in the navigation system to help substrate ablation, but only if they are obtained from high spatial resolution late gadolinium enhancement (LGE)-CMR images. One recent publication showed that CMR-aided scar dechanneling was associated with a lower need for ablation delivery, higher non-inducibility rates after substrate ablation, and reduced VT recurrences in the follow-up. In brief, in this experience the target ablation sites were the conducting channels (CC) entrances (i.e. entrances of VT isthmuses) identified in the substrate EAM, but PSI maps integrated into the navigation system were used to focus on specific regions of the scar. The authors found 23% of false negative (CCs evidence outside the HTCs entrances) and 16% of false positives (HTCs only identified in PSI maps). The HTCs identified only in the PSI maps, without matching with a CC on the EAM, were not targeted for ablation. Very recently, the same group presented results about a possible improvement of the outcome (particularly the efficiency, but probably with extension to efficacy and safety) using a CMR guided ablation, targeting only the HCTs (all of them). However, both experiences with CMR aided and guided ablation had been performed with a retrospective design and in a single-centre high volume laboratory, and for this reason we don't know the potential application of this technique in the real world of clinical electrophysiology.

The investigators sought to evaluate the feasibility, efficacy, safety and efficiency of a VT ablation guided or aided by CMR in comparison with VT ablation guided only by EAM (standard approach nowadays).