Preprocedural magnetic resonance imaging for image-guided catheter ablation of scar-related ventricular tachycardia

Cardiac stereotactic body radiation therapy for ventricular tachycardia: Current experience and technical gaps

INTRODUCTION

Despite advances in drug and catheter ablation therapy, long-term recurrence rates for ventricular tachycardia remain suboptimal. Cardiac stereotactic body radiotherapy (SBRT) is a novel treatment that has demonstrated reduction of arrhythmia episodes and favorable short-term safety profile in treatment-refractory patients. Nevertheless, the current clinical experience is early and limited. Recent studies have highlighted variable duration of treatment effect and substantial recurrence rates several months postradiation. Contributing to these differential outcomes are disparate approaches groups have taken in planning and delivering radiation, owing to both technical and knowledge gaps limiting optimization and standardization of cardiac SBRT.

METHODS AND FINDINGS

In this report, we review the historical basis for cardiac SBRT and existing clinical data. We then elucidate the current technical gaps in cardiac radioablation, incorporating the current clinical experience, and summarize the ongoing and needed efforts to resolve them.

CONCLUSION

Cardiac SBRT is an emerging therapy that holds promise for the treatment of ventricular tachycardia. Technical gaps remain, to be addressed by ongoing research and growing clincial experience.

Multi-Modality Imaging for the Identification of Arrhythmogenic Substrates Prior to Electrophysiology Studies

Noninvasive cardiac imaging is crucial for the characterization of patients who are candidates for cardiac ablations, for both procedure planning and long-term management. Multimodality cardiac imaging can provide not only anatomical parameters but even more importantly functional information that may allow a better risk stratification of cardiac patients. Moreover, fusion of anatomical and functional data derived from noninvasive cardiac imaging with the results of endocavitary mapping may possibly allow a better identification of the ablation substrate and also avoid peri-procedural complications. As a result, imaging-guided electrophysiological procedures are associated with an improved outcome than traditional ablation procedures, with a consistently lower recurrence rate.

Multimodality Imaging to Guide Ventricular Tachycardia Ablation in Patients with Non-ischaemic Cardiomyopathy

Catheter ablation is an effective treatment option for ventricular tachycardia (VT) in patients with non-ischaemic cardiomyopathy (NICM). The heterogeneous nature of NICM aetiologies and VT substrate in patients with NICM play a role in long-term ablation outcomes in this population. Over the past decades, more precise identification of NICM aetiologies and better characterisation of various substrates have been made. Application of multimodal imaging has greatly contributed to the accurate diagnosis of NICM subtypes and improved VT ablation strategies. This article summarises the current knowledge of multimodal imaging used in the characterisation of non-ischaemic NICM substrates, procedural planning and image integration for the optimisation of VT ablation.

Magnetic resonance imaging guidance for the optimization of ventricular tachycardia ablation

Catheter ablation has an important role in the management of patients with ventricular tachycardia (VT) but is limited by modest long-term success rates. Magnetic resonance imaging (MRI) can provide valuable anatomic and functional information as well as potentially improve identification of target sites for ablation. A major limitation of current MRI protocols is the spatial resolution required to identify the areas of tissue responsible for VT but recent developments have led to new strategies which may improve substrate assessment. Potential ways in which detailed information gained from MRI may be utilized during electrophysiology procedures include image integration or performing a procedure under real-time MRI guidance. Image integration allows pre-procedural magnetic resonance (MR) images to be registered with electroanatomical maps to help guide VT ablation and has shown promise in preliminary studies. However, multiple errors can arise during this process due to the registration technique used, changes in ventricular geometry between the time of MRI and the ablation procedure, respiratory and cardiac motion. As isthmus sites may only be a few millimetres wide, reducing these errors may be critical to improve outcomes in VT ablation. Real-time MR-guided intervention has emerged as an alternative solution to address the limitations of pre-acquired imaging to guide ablation. There is now a growing body of literature describing the feasibility, techniques, and potential applications of real-time MR-guided electrophysiology. We review whether real-time MR-guided intervention could be applied in the setting of VT ablation and the potential challenges that need to be overcome.

Ventricular Tachycardia (VT) Substrate Characteristics: Insights from Multimodality Structural and Functional Imaging of the VT Substrate Using Cardiac MRI Scar, 123I-Metaiodobenzylguanidine SPECT Innervation, and Bipolar Voltage

Postischemic adaptation results in characteristic myocardial structural and functional changes in the ventricular tachycardia (VT) substrate. The aim of this study was to compare myocardial structural and functional adaptations (late gadolinium enhancement/abnormal innervation) with detailed VT mapping data to identify regional heterogeneities in postischemic changes. Methods: Fifteen patients with ischemic cardiomyopathy and drug-refractory VT underwent late gadolinium enhancement cardiac MRI (CMR), ¹²³I-metaiodobenzylguanidine SPECT, and high-resolution bipolar voltage mapping to assess fibrosis (>3 SDs), abnormal innervation (<50% tracer uptake), and low-voltage area (<1.5 mV), respectively. Three-dimensional reconstructed CMR/¹²³I-metaiodobenzylguanidine models were coregistered for further comparison. Results: Postischemic structural and functional adaptations in all 3 categories were similar in size (reported as median [quartile 1-quartile 3]: CMR scar, 46.1 cm² [33.1-86.9 cm²]; abnormal innervation, 47.8 cm² [40.5-68.1 cm²]; and low-voltage area, 29.5 cm² [24.5-102.6 cm²]; P > 0.05). However, any single modality underestimated the total VT substrate area defined as abnormal in at least 1 of the 3 modalities (76.0 cm² [57.9-143.2 cm²]; P < 0.001). Within the total VT substrate area, regions abnormal in all 3 modalities were most common (25.2%). However, significant parts of the VT substrate had undergone heterogeneous adaptation (abnormal in <3 modalities); the most common categories were "abnormal innervation only" (18.2%), "CMR scar plus abnormal innervation only" (14.9%), and "CMR scar only" (14.6%). All 14 VT channel/exit sites (0.88 ± 0.74 mV) were localized to myocardium demonstrating CMR scar and abnormal innervation. This specific tissue category accounted for 68.3% of the CMR scar and 31.2% of the total abnormal postischemic VT substrate area. Conclusion: Structural and functional imaging demonstrated regional heterogeneities in the postischemic VT substrate not appreciated by any single modality alone. The coexistence of abnormal innervation and CMR scar may identify a particularly "proarrhythmic" adaptation and may represent a potential novel target for VT ablation.

Cardiac magnetic resonance-aided scar dechanneling: Influence on acute and long-term outcomes

BACKGROUND

Late gadolinium enhancement cardiac magnetic resonance (LGE-CMR) provides tissue characterization of ventricular myocardium and scar that can be depicted as pixel signal intensity (PSI) maps.

OBJECTIVE

To assess the possible benefit of guiding the ventricular tachycardia (VT) substrate mapping by integrating these PSI maps into the navigation system.

METHODS

In total, 159 consecutive patients (66 ± 11 years old, 151 men [95%]) with scar-related left ventricular (LV) VT were included. VT substrate ablation used the scar dechanneling technique. A CMR-aided ablation using the PSI maps was performed in 54 patients (34%). Procedural data as well as acute and long-term outcomes were compared with those of the remaining 105 patients (66%).

RESULTS

Mean procedure duration and fluoroscopy time were 229 ± 67 minutes and 20 ± 9 minutes, respectively, without significant differences between groups. Both the number of radiofrequency (RF) applications and RF delivery time were lower in the CMR-aided group (28 ± 18 applications vs 36 ± 18 applications, P = .037, and 19 ± 12 minutes vs 27 ± 16 minutes, P = .009, respectively). After substrate ablation, monomorphic VT inducibility was lower in the CMR-aided than in the control group (17 [32%] vs 53 [51%] patients, P = .022). After a mean follow-up period of 20 ± 19 months, patients from the CMR-aided group had a lower recurrence rate than those in the control group (10 patients [18.5%] vs 46 patients [43.8%], respectively, P = .002; log-rank P = .017). Multivariate analysis found that CMR-aided ablation (hazard ratio, 0.48 [95% Confirdence Interval (CI) 0.24-0.96], P = .037) was an independent predictor of recurrences.

CONCLUSION

CMR-aided scar dechanneling is associated with a lower need for RF delivery, higher noninducibility rates after substrate ablation, and a higher VT-recurrence-free survival.

Clinical Aspects and Ablation of Ventricular Arrhythmias in Tetralogy of Fallot

Life expectancy of patients with rToF has considerably improved due to refined surgical interventions. Monomorphic fast VTs are frequently encountered in adult patients with rToF. The dominant substrate of VT is anatomical isthmuses bordered by surgical incisions, patch material and valve annuli. Substrate based ablation strategies aim to transect all slow conducting anatomical isthmuses (SCAI) as identified by electroanatomical mapping. Procedural success is defined as non-inducibility of VT and confirmed conduction block over the SCAI resulting in long-term VT free survival in most patients. The identification of SCAIs in rToF may have important implications for risk stratification and preventive treatment.